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Psoriasis in the US Medicare Population: Prevalence, Treatment, and Factors Associated with Biologic Use

  • Junko Takeshita
    Correspondence
    Department of Dermatology, University of Pennsylvania Perelman School of Medicine, Dulles 1104, 3400 Spruce Street, Philadelphia, Pennsylvania 19104, USA
    Affiliations
    Department of Dermatology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA

    Department of Epidemiology and Biostatistics, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
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  • Joel M. Gelfand
    Affiliations
    Department of Dermatology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA

    Department of Epidemiology and Biostatistics, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
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  • Penxiang Li
    Affiliations
    Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA

    Leonard Davis Institute of Health Economics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
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  • Lionel Pinto
    Affiliations
    Amgen, Thousand Oaks, California, USA
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  • Xinyan Yu
    Affiliations
    Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA

    Leonard Davis Institute of Health Economics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
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  • Preethi Rao
    Affiliations
    Leonard Davis Institute of Health Economics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA

    Health Care Management and Economics, The Wharton School at University of Pennsylvania, Philadelphia, Pennsylvania, USA
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  • Hema N. Viswanathan
    Affiliations
    Amgen, Thousand Oaks, California, USA
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  • Jalpa A. Doshi
    Affiliations
    Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA

    Leonard Davis Institute of Health Economics, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania, USA
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      Psoriasis is a common chronic inflammatory disorder, primarily of the skin. Despite an aging population, knowledge of the epidemiology of psoriasis and its treatments among the elderly is limited. We examined the prevalence of psoriasis and its treatments, with a focus on biologics and identification of factors associated with biologic use, using a nationally representative sample of Medicare beneficiaries in 2011. On the basis of several psoriasis identification algorithms, the claims-based prevalence for psoriasis in the United States ranged from 0.51 to 1.23%. Treatments used for moderate-to-severe psoriasis (phototherapy, oral systemic, or biologic therapies) were received by 27.3% of the total psoriasis sample, of whom 37.2% used biologics. Patients without a Medicare Part D low-income subsidy (LIS) had 70% lower odds of having received biologics than those with LIS (odds ratio 0.30; 95% confidence interval, 0.19–0.46). Similarly, the odds of having received biologics were 69% lower among black patients compared with white patients (0.31; 0.16–0.60). This analysis identified potential financial and racial barriers to receipt of biologic therapies and underscores the need for additional studies to further define the epidemiology and treatment of psoriasis among the elderly.
      CI
      confidence interval
      CMS
      Centers for Medicare and Medicaid Services
      ICD-9-CM
      International Classification of Diseases, Ninth Revision, Clinical Modification
      LIS
      low-income subsidy
      OR
      odds ratio
      RxHCC
      prescription drug hierarchical condition category
      SD
      standard deviation

      Introduction

      Psoriasis is a common, chronic, multisystem, inflammatory disease of the skin and sometimes joints. Approximately 7.5 million Americans () are affected by psoriasis, resulting in a prevalence of 2 to 4% in the United States according to population-based estimates (
      • Gelfand J.M.
      • Stern R.S.
      • Nijsten T.
      • et al.
      The prevalence of psoriasis in African Americans: results from a population-based study.
      ;
      • Kurd S.K.
      • Gelfand J.M.
      The prevalence of previously diagnosed and undiagnosed psoriasis in US adults: results from NHANES 2003-2004.
      ;
      • Rachakonda T.D.
      • Schupp C.W.
      • Armstrong A.W.
      Psoriasis prevalence among adults in the United States.
      ). Psoriasis is associated with significant economic (
      • Feldman S.R.
      • Burudpakdee C.
      • Gala S.
      • et al.
      The economic burden of psoriasis: a systematic literature review.
      ), psychosocial (
      • Kimball A.B.
      • Jacobson C.
      • Weiss S.
      • et al.
      The psychosocial burden of psoriasis.
      ), and physical (
      • Yeung H.
      • Takeshita J.
      • Mehta N.N.
      • et al.
      Psoriasis severity and the prevalence of major medical comorbidity: a population-based study.
      ) health burdens that are proportional to disease severity. An increasing body of epidemiologic literature provides evidence that psoriasis, particularly more severe disease, is independently associated with increased risks of major adverse cardiovascular events (
      • Gelfand J.M.
      • Neimann A.L.
      • Shin D.B.
      • et al.
      Risk of myocardial infarction in patients with psoriasis.
      ,
      • Gelfand J.M.
      • Dommasch E.D.
      • Shin D.B.
      • et al.
      The risk of stroke in patients with psoriasis.
      ;
      • Mehta N.N.
      • Azfar R.S.
      • Shin D.B.
      • et al.
      Patients with severe psoriasis are at increased risk of cardiovascular mortality: cohort study using the General Practice Research Database.
      ), diabetes (
      • Azfar R.S.
      • Seminara N.M.
      • Shin D.B.
      • et al.
      Increased risk of diabetes mellitus and likelihood of receiving diabetes mellitus treatment in patients with psoriasis.
      ), renal disease (
      • Wan J.
      • Wang S.
      • Haynes K.
      • et al.
      Risk of moderate to advanced kidney disease in patients with psoriasis: population based cohort study.
      ), and other emerging comorbid diseases (
      • Yeung H.
      • Takeshita J.
      • Mehta N.N.
      • et al.
      Psoriasis severity and the prevalence of major medical comorbidity: a population-based study.
      ).
      Treatment options for psoriasis include topical therapies, phototherapy, and systemic medications. Moderate-to-severe psoriasis, which affects nearly 25% of patients with the disease (), is an indication for treatment with phototherapy, oral systemics (i.e., methotrexate, cyclosporine, or acitretin), or biologics, whereas mild disease is generally treated with topical therapies alone. Psoriatic arthritis, which affects 6 to 17% of patients with psoriasis according to population-based studies (
      • Shbeeb M.
      • Uramoto K.M.
      • Gibson L.E.
      • et al.
      The epidemiology of psoriatic arthritis in Olmsted County, Minnesota, USA, 1982-1991.
      ;
      • Gelfand J.M.
      • Gladman D.D.
      • Mease P.J.
      • et al.
      Epidemiology of psoriatic arthritis in the population of the United States.
      ;
      • Ibrahim G.
      • Waxman R.
      • Helliwell P.S.
      The prevalence of psoriatic arthritis in people with psoriasis.
      ;
      • Wilson F.C.
      • Icen M.
      • Crowson C.S.
      • et al.
      Incidence and clinical predictors of psoriatic arthritis in patients with psoriasis: a population-based study.
      ;
      • Ogdie A.
      • Langan S.
      • Love T.
      • et al.
      Prevalence and treatment patterns of psoriatic arthritis in the UK.
      ;
      • Lofvendahl S.
      • Theander E.
      • Svensson A.
      • et al.
      Validity of diagnostic codes and prevalence of physician-diagnosed psoriasis and psoriatic arthritis in southern Sweden—a population-based register study.
      ), is an indication for treatment with oral systemic or biologic therapies. In the last decade, several new therapies for moderate-to-severe psoriasis have been approved, primarily driven by the development of targeted biologics including tumor necrosis factor, IL-12/-23, and IL-17 inhibitors. Yet most psoriasis patients remain inadequately treated and dissatisfied with their therapies (
      • Horn E.J.
      • Fox K.M.
      • Patel V.
      • et al.
      Are patients with psoriasis undertreated? Results of National Psoriasis Foundation survey.
      ;
      • Armstrong A.W.
      • Robertson A.D.
      • Wu J.
      • et al.
      Undertreatment, treatment trends, and treatment dissatisfaction among patients with psoriasis and psoriatic arthritis in the United States: findings from the National Psoriasis Foundation surveys, 2003-2011.
      ). Furthermore, access to biologics remains a challenge for many patients because of limited insurance coverage, prohibitive costs, and other factors (
      • Polinski J.M.
      • Mohr P.E.
      • Johnson L.
      Impact of Medicare Part D on access to and cost sharing for specialty biologic medications for beneficiaries with rheumatoid arthritis.
      ;
      • Kamangar F.
      • Isip L.
      • Bhutani T.
      • et al.
      How psoriasis patients perceive, obtain, and use biologic agents: survey from an academic medical center.
      ;
      • Romanelli P.
      • Cavallin L.E.
      • Weiss J.
      • et al.
      A unique psoriasis biologics clinic serving underprivileged patients in the United States.
      ).
      Despite marked progress in the understanding of the epidemiology, pathophysiology, and treatment of psoriasis during recent years, major knowledge gaps still exist, particularly regarding the prevalence of and treatment patterns for psoriasis among the growing elderly population, which, in the United States, is estimated to reach 79.7 million by 2040 (
      • United States Department of Health and Human Services Administration on Aging
      ). As over 90% () of the elderly (65 years and older) population in the United States receive medical coverage through the Medicare system, the aim of our study was to investigate the prevalence of psoriasis among Medicare beneficiaries who are actively receiving medical care, examine their clinical characteristics, and determine the prevalence of psoriasis therapies, with a focus on biologic use and factors associated with receiving biologic treatment.

      Results

      Claims based psoriasis prevalence

      Claims based psoriasis prevalence was determined for 799,607 beneficiaries in the 2011 5% Medicare sample using eight different algorithms (Table 1). Using the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) 696.1 code to identify psoriasis, claims based prevalence ranged from 1.13% (95% confidence interval (CI): 1.10–1.15) using an algorithm identifying at least one inpatient or outpatient claim for psoriasis to 0.51% (95% CI: 0.50–0.53) using an algorithm identifying at least one inpatient or outpatient claim for psoriasis made by a dermatologist. We also explored a broader method of identifying psoriasis using claims for either psoriasis or psoriatic arthritis (ICD-9-CM 696.0). Claims based psoriasis prevalence using this method ranged from 1.23% (95% CI: 1.20–1.25) to 0.60% (95% CI: 0.58–0.61). For our main analyses, we identified psoriasis by the presence of at least two inpatient or outpatient claims for psoriasis, which resulted in a prevalence of 0.58% (95% CI: 0.56–0.60).
      Table 1Claims based psoriasis prevalence
      Of 799,607 beneficiaries in the 2011 5% Medicare sample.
      Psoriasis identification algorithmN% (95% Confidence interval)
      ICD-9-CM 696.1 (psoriasis)
       At least 1 inpatient or outpatient claim9,0171.13 (1.10–1.15)
       At least 1 inpatient or 2 outpatient claims4,9250.62 (0.60–0.63)
       At least 2 inpatient or outpatient claims4,6380.58 (0.56–0.60)
       At least 1 inpatient or outpatient claim by dermatologist4,0960.51 (0.50–0.53)
      ICD-9-CM 696.1 (psoriasis) or 696.0 (psoriatic arthritis)
       At least 1 inpatient or outpatient claim9,8271.23 (1.20–1.25)
       At least 1 inpatient or 2 outpatient claims5,6950.71 (0.69–0.73)
       At least 2 inpatient or outpatient claims5,3980.68 (0.66–0.69)
       At least 1 inpatient or outpatient claim by dermatologist or rheumatologist4,7720.60 (0.58–0.61)
      Abbreviation: ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification.
      1 Of 799,607 beneficiaries in the 2011 5% Medicare sample.

      Psoriasis patient characteristics

      Psoriasis patient and Medicare plan characteristics are summarized in Table 2. The mean age of psoriasis patients was 68.6 years (standard deviation (SD), 13.4); 43.2% were male, and 88.8% were white. Regional distribution was as follows: 24.0% in the Northeast, 23.0% in the Midwest, 36.2% in the South, and 16.6% in the West. County-level mean per capita income was $40,115 (SD, $11,817). Average number of dermatologists per 100,000 county residents was 3.6 (SD, 3.6). The majority of beneficiaries qualified for Medicare based on age alone (63.6%). Most beneficiaries were not receiving a Medicare Part D low-income subsidy (LIS) (58.4%). Only 19.0% of the beneficiaries were receiving Part D plans with enhanced alternative coverage. The most commonly coded comorbidities among beneficiaries with psoriasis were cardiometabolic disorders: 67.6% with hypertension, 59.9% with dyslipidemia, and 32.4% with diabetes; 23.5% had atherosclerotic outcomes. In contrast, the prevalence of obesity was relatively low at 9.3%. The prevalence of psoriatic arthritis was 9.4%, which is similar to population-based estimates of psoriatic arthritis among patients with psoriasis (
      • Ogdie A.
      • Langan S.
      • Love T.
      • et al.
      Prevalence and treatment patterns of psoriatic arthritis in the UK.
      ). Other comorbid diseases of interest include inflammatory bowel disease (1.2%), liver disease (5.1%), depression (17.1%), and renal disease (9.8%). As indicators of overall comorbidity, the average number of non-psoriasis medications received was 4.7 (SD, 3.4), and the mean prescription drug hierarchical condition category (RxHCC) score was 1.0 (SD, 0.6).
      Table 2Psoriasis patient characteristics
      Psoriasis is defined by at least two inpatient or outpatient claims for psoriasis (ICD-9-CM 696.1).
      CharacteristicNumber (%)

      N=4,638
      Age, mean (SD)68.6 (13.4)
      Age (category)
       <651,237 (26.7)
       65–69934 (20.1)
       70–74912 (19.7)
       75–79681 (14.7)
       ≥80874 (18.8)
      Sex, male2,002 (43.2)
      Race
       White4,118 (88.8)
       Black236 (5.1)
       Latino104 (2.2)
       Other/unknown180 (3.9)
      Census region
       Northeast1,113 (24.0)
       Midwest1,069 (23.0)
       South1,678 (36.2)
       West770 (16.6)
      County-level characteristics
       Income, per capita/10,000, mean (SD)4.0 (1.2)
       County poverty rate,
      County poverty rate is defined as the percentage of persons in the county living in poverty.
      mean (SD)
      15.5 (5.3)
       Residence in urban county3,611 (78.2)
       Residence in county with low educational level
      County with low educational level is defined by at least 25% of residents not having a high school diploma or GED in the patient’s county of residence.
      520 (11.3)
       Number of primary care providers
      Primary care providers included medical providers practicing in the fields of general family medicine, general practice, and general internal medicine.
      per 10,000 residents, mean (SD)
      6.3 (3.0)
       Number of dermatologists per 100,000 residents, mean (SD)3.6 (3.6)
      Medicare eligibility
       Aged2,952 (63.6)
       Disabled1,237 (26.7)
       Aged plus disabled449 (9.7)
      LIS status
       Full1,838 (39.6)
       Partial47 (1.0)
       None2,709 (58.4)
       Mixed44 (0.9)
      Comorbidities
       AIDS/HIV18 (0.39)
       Autoimmune disease
        Ankylosing spondylitis74 (1.6)
        Inflammatory bowel disease55 (1.2)
        Rheumatoid arthritis290 (6.3)
        Rheumatologic disease382 (8.2)
       Cardiometabolic disease
        Cerebrovascular disease497 (10.7)
        Congestive heart failure515 (11.1)
        Diabetes1,503 (32.4)
        Dyslipidemia2,776 (59.9)
        Hypertension3,137 (67.6)
        Myocardial infarction159 (3.4)
        Obesity431 (9.3)
        Peripheral vascular disease636 (13.7)
        Atherosclerotic outcomes (aggregate of cerebrovascular disease, myocardial infarction, and peripheral vascular disease)1,091 (23.5)
       Hemiplegia or paraplegia49 (1.1)
       Liver disease
        Mild liver disease208 (4.5)
        Moderate-to-severe liver disease27 (0.58)
       Malignant disease
        Cancer518 (11.2)
        Metastatic solid tumor37 (0.80)
       Neuropsychiatric disease
        Dementia134 (2.9)
        Depression794 (17.1)
       Peptic ulcer disease59 (1.3)
       Psoriatic arthritis436 (9.4)
       Pulmonary disease, chronic1,108 (23.9)
       Renal disease455 (9.8)
      Non-psoriasis medications
       Number of 30-day supply equivalent prescriptions for non-psoriasis medications, mean (SD)4.7 (3.4)
      Type of Medicare Part D plan
      Basic plans include defined standard benefit, actuarially equivalent standard, and basic alternative type of Part D plans. Enhanced plans include enhanced alternative type of Part D plans.
       Basic3,491 (75.3)
       Enhanced879 (19.0)
       Unknown268 (5.8)
       RxHCC score, mean (SD)1.0 (0.6)
      Abbreviations: GED, general educational development; ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification; LIS, low-income subsidy; RxHCC, prescription drug hierarchical condition category risk score; SD, standard deviation.
      1 Psoriasis is defined by at least two inpatient or outpatient claims for psoriasis (ICD-9-CM 696.1).
      2 County poverty rate is defined as the percentage of persons in the county living in poverty.
      3 County with low educational level is defined by at least 25% of residents not having a high school diploma or GED in the patient’s county of residence.
      4 Primary care providers included medical providers practicing in the fields of general family medicine, general practice, and general internal medicine.
      5 Basic plans include defined standard benefit, actuarially equivalent standard, and basic alternative type of Part D plans. Enhanced plans include enhanced alternative type of Part D plans.

      Psoriasis therapy prevalence

      The prevalence of therapies received by Medicare beneficiaries with psoriasis is summarized in Table 3. Most patients had at least one claim for psoriasis therapy (83.5%), and 16.5% received no therapy. Topical therapies were used by 76.6% (N=3,551), the majority of whom received topical corticosteroids (97.9%). Phototherapy was used by 7% (N=324). Oral systemic medications were used by 14.3% (N=664), the majority of whom received methotrexate (85.7%). Biologics were received by 10.2% (N=471), among whom specific biologic use was distributed as follows: 44.4% etanercept, 34.2% adalimumab, 22.7% infliximab, and 7.9% ustekinumab. Among biologic users, 31.0% used a physician-administered drug (i.e., alefacept, infliximab, or ustekinumab), and 78.6% used a self-administered medication (i.e., adalimumab or etanercept). Of those who used biologics, 61.8% of patients received biologics only (with or without topical therapies), and the remaining 38.2% also received oral systemics and/or phototherapy during the year.
      Table 3Psoriasis therapy prevalence
      Psoriasis is defined by at least two inpatient or outpatient claims for psoriasis (ICD-9-CM 696.1).
      TherapyNumber (%)
      Percentages do not equal 100 because patients may have received more than one therapy.


      N=4,638
      Topicals
      Coal tar/anthralin use was examined but not reported separately per CMS data use agreement because of cell size of 10 or less.
      3,551 (76.6)
       Corticosteroids3,477 (75.0)
        Class I1,846 (39.8)
        Non-class I2,718 (58.6)
       Calcineurin inhibitors121 (2.6)
       Vitamin D analogs643 (13.9)
       Retinoids21 (0.45)
       Salicylic acid12 (0.17)
      Phototherapy324 (7.0)
       Psoralen plus UVA34 (0.73)
      Excimer laser126 (2.7)
      Oral systemics664 (14.3)
       Methotrexate569 (12.3)
       Cyclosporine22 (0.47)
       Acitretin90 (1.9)
      Biologics
      Alefacept was examined but not reported separately per CMS data use agreement because of cell size of 10 or less.
      471 (10.2)
       Part B (physician-administered)146 (3.1)
        Infliximab107 (2.3)
        Ustekinumab37 (0.80)
       Part D (self-injectables)370 (8.0)
        Adalimumab161 (3.5)
        Etanercept209 (4.5)
      Abbreviations: CMS, Centers for Medicare and Medicaid Services; ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification.
      1 Psoriasis is defined by at least two inpatient or outpatient claims for psoriasis (ICD-9-CM 696.1).
      2 Percentages do not equal 100 because patients may have received more than one therapy.
      3 Coal tar/anthralin use was examined but not reported separately per CMS data use agreement because of cell size of 10 or less.
      4 Alefacept was examined but not reported separately per CMS data use agreement because of cell size of 10 or less.
      In the absence of direct measures of psoriasis severity in claims data, we used psoriasis treatment as a surrogate to define mild versus moderate-to-severe disease. Patients who received either no therapy or topical therapies only were considered to have mild psoriasis and those who received phototherapy, oral systemics, or biologics were considered to have moderate-to-severe psoriasis. Using this method, 70.9% of patients had mild disease, and 27.3% had moderate-to-severe disease (Table 4). Of patients identified to have moderate-to-severe psoriasis, phototherapy was used by 25.6%, oral systemics by 52.4%, and biologics by 37.2%.
      Table 4Psoriasis severity
      Severity defined by therapyNumber (%)
      Percentages do not equal 100 because patients may have received more than one therapy.


      N=4,638
      Mild (n=3,289; 70.9%)
       No therapy763 (23.2)
      Percentages are calculated among those with mild psoriasis.
       Topicals only2,526 (76.8)
      Percentages are calculated among those with mild psoriasis.
      Moderate-to-severe
      Alefacept was included as a biologic therapy to identify moderate-to-severe psoriasis but not reported separately per CMS data use agreement because of cell size of 10 or less.
      (n=1,267; 27.3%)
       Phototherapy324 (25.6)
      Percentages are calculated among those with moderate-to-severe psoriasis.
       Oral systemics664 (52.4)
      Percentages are calculated among those with moderate-to-severe psoriasis.
        Methotrexate569 (44.9)
      Percentages are calculated among those with moderate-to-severe psoriasis.
        Cyclosporine22 (1.7)
      Percentages are calculated among those with moderate-to-severe psoriasis.
        Acitretin90 (7.1)
      Percentages are calculated among those with moderate-to-severe psoriasis.
       Biologics471 (37.2)
      Percentages are calculated among those with moderate-to-severe psoriasis.
        Adalimumab161 (12.7)
      Percentages are calculated among those with moderate-to-severe psoriasis.
        Etanercept209 (44.4)
      Percentages are calculated among those with moderate-to-severe psoriasis.
        Infliximab107 (16.5)
      Percentages are calculated among those with moderate-to-severe psoriasis.
        Ustekinumab37 (2.9)
      Percentages are calculated among those with moderate-to-severe psoriasis.
      Unknown (n=82; 1.8%)
      Abbreviation: CMS, Centers for Medicare and Medicaid Services.
      1 Percentages do not equal 100 because patients may have received more than one therapy.
      2 Percentages are calculated among those with mild psoriasis.
      3 Alefacept was included as a biologic therapy to identify moderate-to-severe psoriasis but not reported separately per CMS data use agreement because of cell size of 10 or less.
      4 Percentages are calculated among those with moderate-to-severe psoriasis.

      Factors associated with biologic use

      In multivariate analyses, we identified factors associated with biologic use among patients receiving therapies consistent with moderate-to-severe psoriasis. Factors associated with a lower likelihood of receiving biologics were as follows: higher primary care provider density (odds ratio (OR) 0.92; 95% CI: 0.86–0.98), absence of Part D LIS (OR 0.30; 95% CI: 0.19–0.46), black race (OR 0.31; 95% CI: 0.16–0.60), and comorbid cancer (OR 0.47; 95% CI: 0.31–0.72) and dementia (OR 0.26; 95% CI: 0.07–0.97) (Table 5). Factors associated with a greater likelihood of biologic use included the following: higher dermatology provider density (OR 1.08; 95% CI: 1.01–1.16), residence in an urban county (OR 1.54; 95% CI: 1.13–2.11), and comorbid ankylosing spondylitis (OR 2.26; 95% CI; 1.13–4.53), inflammatory bowel disease (OR 8.11; 95% CI: 1.91–34.5), psoriatic arthritis (OR 3.79; 95% CI: 2.74–5.24), and renal disease (OR: 2.03, 95% CI: 1.24–3.35).
      Table 5Factors associated with biologic use among patients receiving therapy indicated for moderate to severe psoriasis
      Moderate to severe psoriasis is identified by receipt of either phototherapy, oral systemic, or biologic therapy.
      CharacteristicsStatusUnadjusted odds ratio (95% confidence interval)Adjusted odds ratio
      On the basis of a multivariable logistic regression model including the following covariates: age, sex, race, census region of residence, county-level per-capita income, county-level poverty rate, county-level urban versus rural status, county-level low educational level, density of dermatologists and adult primary care providers per number of residents in the patient’s county of residence, part D plan type, low-income subsidy status, number of non-psoriasis medications, RxHCC score, and comorbid disease status including all components of the Charlson comorbidity index, autoimmune diseases for which biologic therapies are indicated, cardiovascular risk factors, and aggregate of atherosclerotic outcomes.
      (95% confidence interval)
      Adjusted rate, % (95% confidence interval)
      Factors associated with higher odds of biologic use
       Dermatology provider density1.01 (0.98–1.04)1.08 (1.01–1.16)
      3.4 per 100,000 (sample mean)37.4 (35.3–39.5)
      4.4 per 100,000 (one unit increase)38.9 (36.4–41.3)
       Residence in Urban CountyNoReference31.5 (26.9–36.1)
      Yes1.22 (0.94–1.60)1.54 (1.13–2.11)39.2 (36.8–41.7)
       Ankylosing spondylitisNoReference37.3 (35.2–39.4)
      Yes2.52 (1.24–5.09)2.26 (1.13–4.53)52.5 (39.2–65.9)
       Inflammatory bowel diseaseNoReference37.3 (35.2–39.4)
      Yes7.46 (2.29–24.3)8.11 (1.91–34.5)75.6 (53.5–97.7)
       Psoriatic arthritisNoReference30.7 (28.2–33.2)
      Yes3.71 (2.85–4.83)3.79 (2.74–5.24)57.3 (51.8–62.8)
       Renal diseaseNoReference36.1 (33.8–38.4)
      Yes1.45 (1.00–2.11)2.03 (1.24–3.35)49.5 (40.6–58.5)
      Factors Associated with Lower Odds of Biologic Use
       Primary care provider density0.98 (0.94–1.01)0.92 (0.86–0.98)
      6.2 per 10,000 (sample mean)36.9 (34.8–39.1)
      7.2 per 10,000 (one unit increase)35.8 (33.4–38.1)
       Part D low-income subsidyFullReference50.6 (44.9–56.3)
      None0.36 (0.29–0.45)0.30 (0.19–0.46)27.2 (23.5–30.9)
       RaceWhiteReference38.2 (35.9–40.5)
      Black0.55 (0.31–0.99)0.31 (0.16–0.60)19.8 (11.4–28.1)
       CancerNoReference38.2 (35.9–40.5)
      Yes0.38 (0.26–0.56)0.47 (0.31–0.72)25.7 (19.4–31.9)
       DementiaNoReference37.7 (35.5–39.8)
      Yes0.41 (0.13–1.28)0.26 (0.07–0.97)17.2 (2.1–32.3)
      Abbreviation: RxHCC, prescription drug hierarchical condition category risk score.
      1 Moderate to severe psoriasis is identified by receipt of either phototherapy, oral systemic, or biologic therapy.
      2 On the basis of a multivariable logistic regression model including the following covariates: age, sex, race, census region of residence, county-level per-capita income, county-level poverty rate, county-level urban versus rural status, county-level low educational level, density of dermatologists and adult primary care providers per number of residents in the patient’s county of residence, part D plan type, low-income subsidy status, number of non-psoriasis medications, RxHCC score, and comorbid disease status including all components of the Charlson comorbidity index, autoimmune diseases for which biologic therapies are indicated, cardiovascular risk factors, and aggregate of atherosclerotic outcomes.

      Discussion

      In this nationally representative sample of Medicare fee-for-service beneficiaries with Part D drug coverage, we determined claims based psoriasis prevalence and examined the clinical characteristics, treatment prevalence, and factors associated with biologic use for patients with psoriasis. Claims based psoriasis prevalence ranged from 0.51 to 1.23%, depending on the identification algorithm used. These prevalence estimates were lower than what has been reported in population-based studies (
      • Gelfand J.M.
      • Stern R.S.
      • Nijsten T.
      • et al.
      The prevalence of psoriasis in African Americans: results from a population-based study.
      ;
      • Kurd S.K.
      • Gelfand J.M.
      The prevalence of previously diagnosed and undiagnosed psoriasis in US adults: results from NHANES 2003-2004.
      ;
      • Rachakonda T.D.
      • Schupp C.W.
      • Armstrong A.W.
      Psoriasis prevalence among adults in the United States.
      ), perhaps because patients with milder disease do not seek medical care for their skin disease and/or because of the presence of other barriers to receiving psoriasis care. The distribution of comorbid diseases among psoriasis patients was as expected, with the most common comorbidities being related to cardiometabolic disease. With the exception of obesity, the prevalence of cardiometabolic comorbidities was generally greater than what has previously been reported for the general population (
      • Neimann A.L.
      • Shin D.B.
      • Wang X.
      • et al.
      Prevalence of cardiovascular risk factors in patients with psoriasis.
      ;
      • Yeung H.
      • Takeshita J.
      • Mehta N.N.
      • et al.
      Psoriasis severity and the prevalence of major medical comorbidity: a population-based study.
      ), and is likely, in part, attributable to our focus on an elderly population that is more likely to suffer from comorbid conditions (
      • Sundquist J.
      • Winkleby M.A.
      • Pudaric S.
      Cardiovascular disease risk factors among older black, Mexican-American, and white women and men: an analysis of NHANES III, 1988-1994. Third National Health and Nutrition Examination Survey.
      ). Prevalence of cardiometabolic diseases and outcomes may also be affected by misclassification (
      • Quan H.
      • Li B.
      • Saunders L.D.
      • et al.
      Assessing validity of ICD-9-CM and ICD-10 administrative data in recording clinical conditions in a unique dually coded database.
      ). The prevalence of psoriatic arthritis claims was in accordance with population-based estimates of 6 to 17% for psoriasis patients (
      • Shbeeb M.
      • Uramoto K.M.
      • Gibson L.E.
      • et al.
      The epidemiology of psoriatic arthritis in Olmsted County, Minnesota, USA, 1982-1991.
      ;
      • Gelfand J.M.
      • Gladman D.D.
      • Mease P.J.
      • et al.
      Epidemiology of psoriatic arthritis in the population of the United States.
      ;
      • Ibrahim G.
      • Waxman R.
      • Helliwell P.S.
      The prevalence of psoriatic arthritis in people with psoriasis.
      ;
      • Wilson F.C.
      • Icen M.
      • Crowson C.S.
      • et al.
      Incidence and clinical predictors of psoriatic arthritis in patients with psoriasis: a population-based study.
      ;
      • Ogdie A.
      • Langan S.
      • Love T.
      • et al.
      Prevalence and treatment patterns of psoriatic arthritis in the UK.
      ;
      • Lofvendahl S.
      • Theander E.
      • Svensson A.
      • et al.
      Validity of diagnostic codes and prevalence of physician-diagnosed psoriasis and psoriatic arthritis in southern Sweden—a population-based register study.
      ).
      In our study, 16.4% of patients were not receiving treatment for their psoriasis; this is lower than the approximately 40% of patients with psoriasis who were reported to not be receiving treatment in two published surveys of members (
      • Horn E.J.
      • Fox K.M.
      • Patel V.
      • et al.
      Are patients with psoriasis undertreated? Results of National Psoriasis Foundation survey.
      ;
      • Armstrong A.W.
      • Robertson A.D.
      • Wu J.
      • et al.
      Undertreatment, treatment trends, and treatment dissatisfaction among patients with psoriasis and psoriatic arthritis in the United States: findings from the National Psoriasis Foundation surveys, 2003-2011.
      ). Similar to claims based psoriasis prevalence, we suspect that the prevalence of untreated psoriasis patients in our study is an underestimate because of our inability to capture those patients, especially with mild disease, who are not receiving care for their psoriasis. Phototherapy was received by a mere 7% of patients. This observation is consistent with the declining phototherapy usage rates observed in the United States (
      • Housman T.S.
      • Rohrback J.M.
      • Fleischer Jr, A.B.
      • et al.
      Phototherapy utilization for psoriasis is declining in the United States.
      ;
      • Shaw M.K.
      • Davis S.A.
      • Feldman S.R.
      • et al.
      Trends in systemic psoriasis treatment therapies from 1993 through 2010.
      ), which are suggested to result from a combination of factors including poor reimbursement rates (especially for Medicare recipients) (), greater out-of-pocket costs to patients compared with biologics (
      • Yentzer B.A.
      • Yelverton C.B.
      • Simpson G.L.
      • et al.
      Paradoxical effects of cost reduction measures in managed care systems for treatment of severe psoriasis.
      ), and greater time commitment required from the patient, despite phototherapy being a first-line, effective, and a well-tolerated treatment for moderate-to-severe psoriasis (
      • Menter A.
      • Gottlieb A.
      • Feldman S.R.
      • et al.
      Guidelines of care for the management of psoriasis and psoriatic arthritis: section 1. Overview of psoriasis and guidelines of care for the treatment of psoriasis with biologics.
      ). Oral systemic medications, namely methotrexate, were found to be the most common treatments for beneficiaries receiving therapies used for moderate-to-severe psoriasis, followed by biologics with approximately one-third of beneficiaries having received a biologic in 2011. Among biologic therapies, self-administered biologics were used by most patients, perhaps reflecting patient preferences for subcutaneous self-injectables over intravenous biologics, a finding suggested by previous studies of patients with rheumatoid arthritis who are candidates for similar biologics (
      • Barton J.L.
      Patient preferences and satisfaction in the treatment of rheumatoid arthritis with biologic therapy.
      ;
      • Huynh T.K.
      • Ostergaard A.
      • Egsmose C.
      • et al.
      Preferences of patients and health professionals for route and frequency of administration of biologic agents in the treatment of rheumatoid arthritis.
      ). The prevalence of ustekinumab claims in our study was predictably low, perhaps owing to its more recent approval by the Food and Drug Administration for treatment of moderate-to-severe psoriasis in September 2009 compared with the other biologics.
      Examination of the factors associated with biologic use among those patients receiving therapies used to treat moderate-to-severe psoriasis revealed both expected and, to our knowledge, previously unreported findings. Medicare beneficiaries lacking LIS under the Part D plan had 70% lower odds of receiving biologics compared with their counterparts with LIS that allowed for minimal out-of-pocket drug costs for self-injectable biologics (approximately $3 to $6 copayment depending on income levels), independent of other patient and plan characteristics. Moreover, patients without LIS may face substantially greater costs for several of the Part D covered biologics with 25 to 33% co-insurance within the initial coverage limit and 50% of the drug costs in the Part D coverage gap. We also found black beneficiaries to be approximately 70% less likely to receive biologics compared with white beneficiaries. LIS status (
      • Zhang J.
      • Xie F.
      • Delzell E.
      • et al.
      Trends in the use of biologic agents among rheumatoid arthritis patients enrolled in the US medicare program.
      ) and black race (
      • Schmajuk G.
      • Trivedi A.N.
      • Solomon D.H.
      • et al.
      Receipt of disease-modifying antirheumatic drugs among patients with rheumatoid arthritis in Medicare managed care plans.
      ;
      • Solomon D.H.
      • Ayanian J.Z.
      • Yelin E.
      • et al.
      Use of disease-modifying medications for rheumatoid arthritis by race and ethnicity in the National Ambulatory Medical Care Survey.
      ;
      • Chu L.H.
      • Portugal C.
      • Kawatkar A.A.
      • et al.
      Racial/ethnic differences in the use of biologic disease-modifying antirheumatic drugs among California Medicaid rheumatoid arthritis patients.
      ) have been similarly associated with biologic use in studies of patients with rheumatoid arthritis. Together, these findings suggest the presence of economic and racial factors that may impact the treatment of moderate-to-severe psoriasis and merit further study.
      Expectedly, higher dermatology provider density and residence in an urban county setting were each associated with greater odds of receiving biologics. The presence of comorbidities for which biologic treatment is indicated (i.e., ankylosing spondylitis, inflammatory bowel disease, and psoriatic arthritis) was also associated with greater odds of receiving biologics. Patients with a history of renal disease were twice as likely to receive biologic therapy as patients without renal disease, likely because of the relative contraindication to methotrexate use among those with renal insufficiency. On the other hand, patients with a history of cancer, a relative contraindication to biologics, and those with dementia were less likely to receive biologics compared with patients without cancer and dementia, respectively. Finally, it is notable that the likelihood of receiving a biologic did not differ between those who qualified for Medicare based on their age versus those who qualified because of disability.
      Our study has several strengths, including the use of Medicare claims data that are representative of the elderly (65 years and older) population in the United States, 93% of whom were enrolled in Medicare in 2011 (Centers for Medicare and Medicaid Services, 2011), making our findings generalizable to the majority of this population who has fee-for-service Medicare with Part D drug coverage. Medicare data have high-quality information on demographics, clinical encounters, and prescriptions for beneficiaries. In particular, race data have been shown to be valid for whites and blacks (
      • Zaslavsky A.M.
      • Ayanian J.Z.
      • Zaborski L.B.
      The validity of race and ethnicity in enrollment data for Medicare beneficiaries.
      ). There are also several limitations of our study to consider. Misclassification of psoriasis (
      • Icen M.
      • Crowson C.S.
      • McEvoy M.T.
      • et al.
      Potential misclassification of patients with psoriasis in electronic databases.
      ) and comorbidities (
      • Quan H.
      • Li B.
      • Saunders L.D.
      • et al.
      Assessing validity of ICD-9-CM and ICD-10 administrative data in recording clinical conditions in a unique dually coded database.
      ) as identified by administrative claims is possible. We identified patients with psoriasis by the presence of at least two claims for ICD-9-CM 696.1, which has been suggested to have a positive predictive value of 70% (
      • Icen M.
      • Crowson C.S.
      • McEvoy M.T.
      • et al.
      Potential misclassification of patients with psoriasis in electronic databases.
      ). This definition was preferred over that of at least one claim for psoriasis by a dermatologist in order to balance our efforts to minimize misclassification and avoid selection of a more severe population of psoriasis patients who would be more likely to see a dermatologist. Furthermore, because our study relies on medical claims to identify patients with psoriasis, our results may underestimate the true prevalence of psoriasis among the elderly. Our study also encompasses data from 2011 that may not be representative of the current state of psoriasis treatment among the elderly, particularly for those receiving ustekinumab, which was approved for psoriasis in September 2009. As data on direct measures of psoriasis severity were unavailable, we used treatment as a proxy to define severity that may have resulted in misclassification. We also lacked information on other patient- and provider-level factors such as individual income or education status, or provider prescription patterns that may further affect biologic use. Finally, our findings may not be generalizable to beneficiaries enrolled in Medicare managed care (i.e., Medicare Advantage or Part C) plans and non-Medicare patient populations.
      Our study is, to our knowledge, the first to examine the epidemiology and treatment of psoriasis in the United States Medicare population. We found the claims based prevalence of psoriasis to be lower than population-based estimates. Cardiometabolic disorders and depression were prevalent among Medicare beneficiaries with psoriasis, confirming previous epidemiologic studies performed in generally younger populations and possibly suggesting an even greater burden of comorbid disease among the elderly psoriasis population. Phototherapy was underutilized, consistent with the decreasing use of phototherapy in the United States (
      • Housman T.S.
      • Rohrback J.M.
      • Fleischer Jr, A.B.
      • et al.
      Phototherapy utilization for psoriasis is declining in the United States.
      ;
      • Shaw M.K.
      • Davis S.A.
      • Feldman S.R.
      • et al.
      Trends in systemic psoriasis treatment therapies from 1993 through 2010.
      ). Oral systemic medications were used by more than half of the Medicare beneficiaries receiving therapies indicated for moderate-to-severe psoriasis, followed closely by biologic use at approximately 37%. Notably, our data identify potential financial and racial barriers to psoriasis patients receiving biologic therapies. To improve psoriasis treatment, future studies should evaluate whether similar barriers also exist for other populations, such as those with private insurance, Medicaid, or other medical coverage programs. Collectively, our findings provide an important addition to the limited literature on psoriasis and its treatments among the elderly and highlight areas for future study.

      Materials and Methods

      Data source, study population, design

      We performed a retrospective claims analysis of the 2011 5% Medicare Chronic Condition Warehouse files available from the United States Centers for Medicare and Medicaid Services (CMS). Medicare is a nationwide health insurance program administered by the United States federal government for the elderly (65 years and older) and the disabled. Medicare data are broadly representative of the elderly population in the United States. We estimated the annual cross-sectional prevalence of psoriasis claims among beneficiaries with continuous fee-for-service Medicare Part A (hospital insurance) and B (medical insurance) coverage and stand-alone Part D (prescription drug) plan enrollment in 2011. In our primary analyses, we also examined patient demographics, socioeconomic status, Medicare plan characteristics, clinical characteristics, and treatments for psoriasis among patients who had at least two inpatient or outpatient claims for psoriasis, identified by ICD-9-CM code 696.1. In secondary analyses, we identified psoriasis by at least one inpatient or outpatient claim for psoriasis by a dermatologist and present data in Supplementary Tables 1–4 online.

      Claims based psoriasis prevalence

      Claims based psoriasis prevalence was examined using eight algorithms (Table 1): (i) at least one inpatient or outpatient claim for ICD-9-CM 696.1 (psoriasis); (ii) at least one inpatient or two outpatient claims for ICD-9-CM 696.1; (iii) at least two inpatient or outpatient claims for ICD-9-CM 696.1; (iv) at least one inpatient or outpatient claim for ICD-9-CM 696.1 by a dermatologist; (v) at least one inpatient or outpatient claim for ICD-9-CM 696.1 or 696.0 (psoriatic arthritis); (vi) at least one inpatient or two outpatient claims for ICD-9-CM 696.1 or 696.0; (vii) at least two inpatient or outpatient claims for ICD-9-CM 696.1 or 696.0; and (viii) at least one inpatient or outpatient claim for ICD-9-CM 696.1 or 696.0 by a dermatologist or a rheumatologist. As most patients with psoriatic arthritis also have psoriasis (
      • Gladman D.D.
      • Antoni C.
      • Mease P.
      • et al.
      Psoriatic arthritis: epidemiology, clinical features, course, and outcome.
      ;
      • Love T.J.
      • Gudbjornsson B.
      • Gudjonsson J.E.
      • et al.
      Psoriatic arthritis in Reykjavik, Iceland: prevalence, demographics, and disease course.
      ), our algorithms explored the use of ICD-9-CM codes for both psoriasis (696.1) and psoriatic arthritis (696.0). Provider specialty was determined using the Medicare provider specialty supplemental file. Algorithm (ii) was used for our main analyses. This algorithm was selected to minimize psoriasis misclassification, avoid limitation of the study population to more severe cases presenting to dermatologists, and minimize inclusion of those with concomitant psoriatic arthritis, as having arthritis may have driven therapy decisions and affected treatment patterns.

      Psoriasis treatments

      We examined the prevalence of topical therapies, phototherapy, and oral systemic and biologic medications used to treat psoriasis among all Medicare beneficiaries with psoriasis. The prevalence of phototherapy, oral systemics, and biologics among patients identified as having moderate-to-severe psoriasis was also determined. Topical therapies included corticosteroids, calcineurin inhibitors, vitamin D analogs, coal tar or anthralin, retinoids (i.e., tazarotene), and salicylic acid. Phototherapy included both UVB and psoralen and UVA. Oral systemic therapies included methotrexate, cyclosporine, and acitretin. Biologic therapies included adalimumab, alefacept, etanercept, infliximab, and ustekinumab.

      Psoriasis severity

      In the absence of direct measures of psoriasis severity in claims data, per convention, the receipt of phototherapy, oral systemic, or biologic was used as a proxy to define moderate-to-severe psoriasis (
      • Gelfand J.M.
      • Neimann A.L.
      • Shin D.B.
      • et al.
      Risk of myocardial infarction in patients with psoriasis.
      ,
      • Gelfand J.M.
      • Shin D.B.
      • Neimann A.L.
      • et al.
      The risk of lymphoma in patients with psoriasis.
      ;
      • Seminara N.M.
      • Abuabara K.
      • Shin D.B.
      • et al.
      Validity of The Health Improvement Network (THIN) for the study of psoriasis.
      ;
      • Wu J.J.
      • Poon K.Y.
      • Channual J.C.
      • et al.
      Association between tumor necrosis factor inhibitor therapy and myocardial infarction risk in patients with psoriasis.
      ). Mild psoriasis was defined by the absence of therapy or the receipt of topical therapies only.

      Variables

      Patient and Medicare plan characteristics served as covariates in regression analyses and were summarized descriptively. Patient demographics and characteristics included age, sex, race, census region of residence, reason for Medicare eligibility (aged or disabled), and Part D LIS status. County-level socioeconomic characteristics included per capita income, poverty rate, urban versus rural status, and low educational level. The density of dermatologists and adult primary care providers per number of residents in the patient’s county of residence was used as a measure of availability of and/or access to dermatologists and primary care providers, respectively. Clinical variables included specific comorbid disease status including other immune-mediated diseases for which biologic therapies are indicated (i.e., ankylosing spondylitis, inflammatory bowel disease, psoriatic arthritis, and rheumatoid arthritis), cardiovascular disease risk factors, an aggregate of atherosclerotic outcomes (i.e., cerebrovascular disease, myocardial infarction, and peripheral vascular disease), components of the Charlson comorbidity index (
      • Quan H.
      • Sundararajan V.
      • Halfon P.
      • et al.
      Coding algorithms for defining comorbidities in ICD-9-CM and ICD-10 administrative data.
      ), and other measures of comorbidity including the total number of non-psoriasis medications, and RxHCC risk score. Each comorbid disease was defined by at least two inpatient or outpatient claims for the disease of interest. The RxHCC score was originally created using the RxHCC model to predict each Medicare beneficiary’s total drug spending in the following year based on indicators for 197 medical conditions identified from Medicare claims (
      • Robst J.
      • Levy J.M.
      • Ingber M.J.
      Diagnosis-based risk adjustment for medicare prescription drug plan payments.
      ). Although the RxHCC risk score was designed for Medicare prescription drug plan payment purposes, it has been used to adjust for potential selection biases in medical and drug use studies among Medicare patients (
      • Doshi J.A.
      • Li P.
      • Puig A.
      Impact of the Medicare Modernization Act of 2003 on utilization and spending for medicare part B-covered biologics in rheumatoid arthritis.
      ;
      • Donohue J.M.
      • Morden N.E.
      • Gellad W.F.
      • et al.
      Sources of regional variation in Medicare Part D drug spending.
      ;
      • Li P.
      • McElligott S.
      • Bergquist H.
      • et al.
      Effect of the Medicare Part D coverage gap on medication use among patients with hypertension and hyperlipidemia.
      ,
      • Li P.
      • Metlay J.P.
      • Marcus S.C.
      • et al.
      Factors associated with antimicrobial drug use in medicaid programs.
      ). Furthermore, the RxHCC model was adapted from the hierarchical condition category risk adjustment model, which has been shown to be a better predictor of mortality compared with other comorbidity measures such as the Charlson and Elixhauser comorbidity indices (
      • Li P.
      • Kim M.M.
      • Doshi J.A.
      Comparison of the performance of the CMS Hierarchical Condition Category (CMS-HCC) risk adjuster with the Charlson and Elixhauser comorbidity measures in predicting mortality.
      ). Unlike the official RxHCC risk score that includes weights for age and sex, our score was based on medical conditions only, allowing us to independently examine age and sex effects in regression analyses. Medicare Part D plans cover drugs that are approved for self-administration (i.e., topicals, orals, and the self-administered biologics adalimumab and etanercept). Part D plan characteristics include type of Part D benefit (defined standard benefit, actuarially equivalent standard, basic alternative, and enhanced alternative). Except for the enhanced alternative benefit, all Part D benefits provide basic benefits, which include defined standard coverage or benefits that are actuarially equivalent to the standard coverage. LIS is generally provided to Part D beneficiaries who are financially disadvantaged and allows for minimal out-of-pocket drug costs to those receiving the subsidy compared with non-LIS beneficiaries.

      Analysis

      We used descriptive statistics to calculate the prevalence of psoriasis claims and summarize demographic, socioeconomic, Medicare plan and comorbid disease characteristics, and psoriasis therapies. Multivariate logistic regressions adjusted for clustering at the Medicare plan level were used to identify the factors associated with biologic use. All variables except for psoriasis therapies were included in the logistic regressions in order to determine which factors were associated with biologic use; the aggregate atherosclerotic outcomes variable was included in place of individual cerebrovascular disease, myocardial infarction, and peripheral vascular disease variables. Parsimonious models removing clinically or statistically nonsignificant variables were also evaluated and produced similar results to the full regression models. Risk-adjusted rates were calculated from the full multivariate logistic regression model. There were no missing data; variables with designated “other” or “unknown” values were included as such. Statistical significance was determined by a two-tailed P-value<0.05. All analyses were performed using Stata (Version 13, StataCorp, College Station, TX).

      Protection of human subjects

      This study was approved by the University of Pennsylvania Institutional Review Board and CMS (Data Use Agreement 25762). Per CMS Data Use Agreement, any data cells containing <11 beneficiaries were not shown. The study was conducted in accordance with the Declaration of Helsinki and reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology guidelines (
      • von Elm E.
      • Altman D.G.
      • Egger M.
      • et al.
      The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
      ).

      ACKNOWLEDGMENTS

      This study was funded by Amgen with additional support from the National Institutes of Health (CTSA UL1RR024134). Dr Takeshita was supported by a Dermatology Foundation Career Development Award; Dr Gelfand was supported by NIAMS K24-AR064310. The sponsors (Amgen) participated in the design and conduct of the study; interpretation of the data; preparation, review and approval of the manuscript; and in the decision to submit the manuscript for publication. The sponsors (Amgen) had no role in the collection, management, or analysis of the data.

      Supplementary material

      Supplementary material is linked to the online version of the paper at http://www.nature.com/jid

      REFERENCES

        • Armstrong A.W.
        • Robertson A.D.
        • Wu J.
        • et al.
        Undertreatment, treatment trends, and treatment dissatisfaction among patients with psoriasis and psoriatic arthritis in the United States: findings from the National Psoriasis Foundation surveys, 2003-2011.
        JAMA Dermatol. 2013; 149: 1180-1185
        • Azfar R.S.
        • Seminara N.M.
        • Shin D.B.
        • et al.
        Increased risk of diabetes mellitus and likelihood of receiving diabetes mellitus treatment in patients with psoriasis.
        Arch Dermatol. 2012; 148: 995-1000
        • Barton J.L.
        Patient preferences and satisfaction in the treatment of rheumatoid arthritis with biologic therapy.
        Patient Prefer Adherence. 2009; 3: 335-344
        • Centers for Medicare and Medicaid Services
        Center for Medicare and Medicaid Services 2011 Data Compendium. 2011 (Accessed on 1 December 2014)
        • Chu L.H.
        • Portugal C.
        • Kawatkar A.A.
        • et al.
        Racial/ethnic differences in the use of biologic disease-modifying antirheumatic drugs among California Medicaid rheumatoid arthritis patients.
        Arthritis Care Res. 2013; 65: 299-303
        • Donohue J.M.
        • Morden N.E.
        • Gellad W.F.
        • et al.
        Sources of regional variation in Medicare Part D drug spending.
        N Engl J Med. 2012; 366: 530-538
        • Doshi J.A.
        • Li P.
        • Puig A.
        Impact of the Medicare Modernization Act of 2003 on utilization and spending for medicare part B-covered biologics in rheumatoid arthritis.
        Arthritis Care Res. 2010; 62: 354-361
        • Feldman S.R.
        • Burudpakdee C.
        • Gala S.
        • et al.
        The economic burden of psoriasis: a systematic literature review.
        Expert Rev Pharmacoecon Outcomes Res. 2014; 14: 685-705
        • Gelfand J.M.
        • Dommasch E.D.
        • Shin D.B.
        • et al.
        The risk of stroke in patients with psoriasis.
        J Invest Dermatol. 2009; 129: 2411-2418
        • Gelfand J.M.
        • Gladman D.D.
        • Mease P.J.
        • et al.
        Epidemiology of psoriatic arthritis in the population of the United States.
        J Am Acad Dermatol. 2005; 53: 573
        • Gelfand J.M.
        • Neimann A.L.
        • Shin D.B.
        • et al.
        Risk of myocardial infarction in patients with psoriasis.
        JAMA. 2006; 296: 1735-1741
        • Gelfand J.M.
        • Shin D.B.
        • Neimann A.L.
        • et al.
        The risk of lymphoma in patients with psoriasis.
        J Invest Dermatol. 2006; 126: 2194-2201
        • Gelfand J.M.
        • Stern R.S.
        • Nijsten T.
        • et al.
        The prevalence of psoriasis in African Americans: results from a population-based study.
        J Am Acad Dermatol. 2005; 52: 23-26
        • Gladman D.D.
        • Antoni C.
        • Mease P.
        • et al.
        Psoriatic arthritis: epidemiology, clinical features, course, and outcome.
        Ann Rheum Dis. 2005; 64: ii14-ii17
        • Horn E.J.
        • Fox K.M.
        • Patel V.
        • et al.
        Are patients with psoriasis undertreated? Results of National Psoriasis Foundation survey.
        J Am Acad Dermatol. 2007; 57: 957-962
        • Housman T.S.
        • Rohrback J.M.
        • Fleischer Jr, A.B.
        • et al.
        Phototherapy utilization for psoriasis is declining in the United States.
        J Am Acad Dermatol. 2002; 46: 557-559
        • Huynh T.K.
        • Ostergaard A.
        • Egsmose C.
        • et al.
        Preferences of patients and health professionals for route and frequency of administration of biologic agents in the treatment of rheumatoid arthritis.
        Patient Prefer Adherence. 2014; 8: 93-99
        • Ibrahim G.
        • Waxman R.
        • Helliwell P.S.
        The prevalence of psoriatic arthritis in people with psoriasis.
        Arthritis Rheum. 2009; 61: 1373-1378
        • Icen M.
        • Crowson C.S.
        • McEvoy M.T.
        • et al.
        Potential misclassification of patients with psoriasis in electronic databases.
        J Am Acad Dermatol. 2008; 59: 981-985
        • Kamangar F.
        • Isip L.
        • Bhutani T.
        • et al.
        How psoriasis patients perceive, obtain, and use biologic agents: survey from an academic medical center.
        J Dermatolog Treat. 2013; 24: 13-24
        • Kimball A.B.
        • Jacobson C.
        • Weiss S.
        • et al.
        The psychosocial burden of psoriasis.
        Am J Clin Dermatol. 2005; 6: 383-392
        • Kurd S.K.
        • Gelfand J.M.
        The prevalence of previously diagnosed and undiagnosed psoriasis in US adults: results from NHANES 2003-2004.
        J Am Acad Dermatol. 2009; 60: 218-224
        • Lebwohl M.
        CMS reduces value of phototherapy codes. 2013 (Accessed on 28 October 2014)
        • Li P.
        • Kim M.M.
        • Doshi J.A.
        Comparison of the performance of the CMS Hierarchical Condition Category (CMS-HCC) risk adjuster with the Charlson and Elixhauser comorbidity measures in predicting mortality.
        BMC Health Serv Res. 2010; 10: 245
        • Li P.
        • McElligott S.
        • Bergquist H.
        • et al.
        Effect of the Medicare Part D coverage gap on medication use among patients with hypertension and hyperlipidemia.
        Ann Intern Med. 2012; 156 (W-263, W-4, W-5, W-6, W-7, W-8, W-9): 776-784
        • Li P.
        • Metlay J.P.
        • Marcus S.C.
        • et al.
        Factors associated with antimicrobial drug use in medicaid programs.
        Emerg Infect Dis. 2014; 20: 829-832
        • Lofvendahl S.
        • Theander E.
        • Svensson A.
        • et al.
        Validity of diagnostic codes and prevalence of physician-diagnosed psoriasis and psoriatic arthritis in southern Sweden—a population-based register study.
        PloS One. 2014; 9: e98024
        • Love T.J.
        • Gudbjornsson B.
        • Gudjonsson J.E.
        • et al.
        Psoriatic arthritis in Reykjavik, Iceland: prevalence, demographics, and disease course.
        J Rheumatol. 2007; 34: 2082-2088
        • Mehta N.N.
        • Azfar R.S.
        • Shin D.B.
        • et al.
        Patients with severe psoriasis are at increased risk of cardiovascular mortality: cohort study using the General Practice Research Database.
        Eur Heart J. 2010; 31: 1000-1006
        • Menter A.
        • Gottlieb A.
        • Feldman S.R.
        • et al.
        Guidelines of care for the management of psoriasis and psoriatic arthritis: section 1. Overview of psoriasis and guidelines of care for the treatment of psoriasis with biologics.
        J Am Acad Dermatol. 2008; 58: 826-850
      1. National Psoriasis Foundation. http://www.psoriasis.org/research/science-of-psoriasis/statistics. Accessed on 1 September 2014

        • Neimann A.L.
        • Shin D.B.
        • Wang X.
        • et al.
        Prevalence of cardiovascular risk factors in patients with psoriasis.
        J Am Acad Dermatol. 2006; 55: 829-835
        • Ogdie A.
        • Langan S.
        • Love T.
        • et al.
        Prevalence and treatment patterns of psoriatic arthritis in the UK.
        Rheumatology. 2013; 52: 568-575
        • Polinski J.M.
        • Mohr P.E.
        • Johnson L.
        Impact of Medicare Part D on access to and cost sharing for specialty biologic medications for beneficiaries with rheumatoid arthritis.
        Arthritis Rheum. 2009; 61: 745-754
        • Quan H.
        • Li B.
        • Saunders L.D.
        • et al.
        Assessing validity of ICD-9-CM and ICD-10 administrative data in recording clinical conditions in a unique dually coded database.
        Health Serv Res. 2008; 43: 1424-1441
        • Quan H.
        • Sundararajan V.
        • Halfon P.
        • et al.
        Coding algorithms for defining comorbidities in ICD-9-CM and ICD-10 administrative data.
        Med Care. 2005; 43: 1130-1139
        • Rachakonda T.D.
        • Schupp C.W.
        • Armstrong A.W.
        Psoriasis prevalence among adults in the United States.
        J Am Acad Dermatol. 2014; 70: 512-516
        • Robst J.
        • Levy J.M.
        • Ingber M.J.
        Diagnosis-based risk adjustment for medicare prescription drug plan payments.
        Health Care Financ Rev. 2007; 28: 15-30
        • Romanelli P.
        • Cavallin L.E.
        • Weiss J.
        • et al.
        A unique psoriasis biologics clinic serving underprivileged patients in the United States.
        J Am Acad Dermatol. 2015; 72: 184-185
        • Schmajuk G.
        • Trivedi A.N.
        • Solomon D.H.
        • et al.
        Receipt of disease-modifying antirheumatic drugs among patients with rheumatoid arthritis in Medicare managed care plans.
        JAMA. 2011; 305: 480-486
        • Seminara N.M.
        • Abuabara K.
        • Shin D.B.
        • et al.
        Validity of The Health Improvement Network (THIN) for the study of psoriasis.
        Br J Dermatol. 2011; 164: 602-609
        • Shaw M.K.
        • Davis S.A.
        • Feldman S.R.
        • et al.
        Trends in systemic psoriasis treatment therapies from 1993 through 2010.
        J Drugs Dermatol. 2014; 13: 917-920
        • Shbeeb M.
        • Uramoto K.M.
        • Gibson L.E.
        • et al.
        The epidemiology of psoriatic arthritis in Olmsted County, Minnesota, USA, 1982-1991.
        J Rheumatol. 2000; 27: 1247-1250
        • Solomon D.H.
        • Ayanian J.Z.
        • Yelin E.
        • et al.
        Use of disease-modifying medications for rheumatoid arthritis by race and ethnicity in the National Ambulatory Medical Care Survey.
        Arthritis Care Res. 2012; 64: 184-189
        • Sundquist J.
        • Winkleby M.A.
        • Pudaric S.
        Cardiovascular disease risk factors among older black, Mexican-American, and white women and men: an analysis of NHANES III, 1988-1994. Third National Health and Nutrition Examination Survey.
        J Am Geriatr Soc. 2001; 49: 109-116
        • United States Department of Health and Human Services Administration on Aging
        A profile of older Americans. 2012 (Accessed on 24 October 2014)
        • von Elm E.
        • Altman D.G.
        • Egger M.
        • et al.
        The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies.
        Lancet. 2007; 370: 1453-1457
        • Wan J.
        • Wang S.
        • Haynes K.
        • et al.
        Risk of moderate to advanced kidney disease in patients with psoriasis: population based cohort study.
        BMJ. 2013; 347: f5961
        • Wilson F.C.
        • Icen M.
        • Crowson C.S.
        • et al.
        Incidence and clinical predictors of psoriatic arthritis in patients with psoriasis: a population-based study.
        Arthritis Rheum. 2009; 61: 233-239
        • Wu J.J.
        • Poon K.Y.
        • Channual J.C.
        • et al.
        Association between tumor necrosis factor inhibitor therapy and myocardial infarction risk in patients with psoriasis.
        Arch Dermatol. 2012; 148: 1244-1250
        • Yentzer B.A.
        • Yelverton C.B.
        • Simpson G.L.
        • et al.
        Paradoxical effects of cost reduction measures in managed care systems for treatment of severe psoriasis.
        Dermatol Online J. 2009; 15: 1
        • Yeung H.
        • Takeshita J.
        • Mehta N.N.
        • et al.
        Psoriasis severity and the prevalence of major medical comorbidity: a population-based study.
        JAMA Dermatol. 2013; 149: 1173-1179
        • Zaslavsky A.M.
        • Ayanian J.Z.
        • Zaborski L.B.
        The validity of race and ethnicity in enrollment data for Medicare beneficiaries.
        Health Serv Res. 2012; 47: 1300-1321
        • Zhang J.
        • Xie F.
        • Delzell E.
        • et al.
        Trends in the use of biologic agents among rheumatoid arthritis patients enrolled in the US medicare program.
        Arthritis Care Res. 2013; 65: 1743-1751