Incidence and prevalence of idiopathic inflammatory myopathies among commercially insured, Medicare supplemental insured, and Medicaid enrolled populations: an administrative claims analysis

Karen E Smoyer-Tomic,Ancilla W Fernandes,Anthony A Amato

doi:10.1186/1471-2474-13-103

Abstract

BackgroundIdiopathic inflammatory myopathies (IIMs) are a rare group of autoimmune syndromes characterized by chronic muscle inflammation and muscle weakness with no known cause. Little is known about their incidence and prevalence. This study reports the incidence and prevalence of IIMs among commercially insured and Medicare and Medicaid enrolled populations in the US.MethodsWe retrospectively examined medical claims with an IIM diagnosis (ICD-9-CM 710.3 [dermatomyositis (DM)], 710.4 [polymyositis (PM)], 728.81[interstitial myositis]) in the MarketScan® databases to identify age- and gender-adjusted annual IIM incidence and prevalence for 2004–2008. Sensitivity analysis was performed for evidence of a specialist visit (rheumatologist/ neurologist/dermatologist), systemic corticosteroid or immunosuppressant use, or muscle biopsy.ResultsWe identified 2,990 incident patients between 2004 and 2008 (67% female, 17% Medicaid enrollees, 27% aged ≥65 years). Overall adjusted IIM incidence for 2004–2008 for commercial and Medicare supplemental groups combined were 4.27 cases (95% CI, 4.09-4.44) and for Medicaid, 5.23 (95% CI 4.74-5.72) per 100,000 person-years (py). Disease sub-type incidence rates per 100,000-py were 1.52 (95% CI 1.42-1.63) and 1.70 (1.42-1.97) for DM, 2.46 (2.33-2.59) and 3.53 (3.13-3.94) for PM, and 0.73 (0.66-0.81) and 0.78 (0.58-0.97) for interstitial myositis for the commercial/Medicare and Medicaid cohorts respectively. Annual incidence fluctuated over time with the base MarketScan populations. There were 7,155 prevalent patients, with annual prevalence ranging from 20.62 to 25.32 per 100,000 for commercial/Medicare (83% of prevalent cases) and from 15.35 to 32.74 for Medicaid.ConclusionsWe found higher IIM incidence than historically reported. Employer turnover, miscoding and misdiagnosing, care seeking behavior, and fluctuations in database membership over time can influence the results. Further studies are needed to confirm the incidence and prevalence of IIM.

Highlights

Idiopathic inflammatory myopathies (IIMs) are a rare group of autoimmune syndromes characterized by chronic muscle inflammation and muscle weakness with no known cause
Autoimmune idiopathic inflammatory myopathies (IIMs) consist of a rare group of autoimmune syndromes characterized by chronic muscle inflammation and muscle weakness
Incident cohort Among nearly 50,750,000 py in the commercial/Medicare databases and close to 9,860,000 py in the Medicaid database, a total of 2,990 incident cases were identified, 2,477 (83%) in the commercially insured/Medicare supplemental databases and 513 (17%) in the Medicaid database (Table 1)

Summary

Introduction

Idiopathic inflammatory myopathies (IIMs) are a rare group of autoimmune syndromes characterized by chronic muscle inflammation and muscle weakness with no known cause. Autoimmune idiopathic inflammatory myopathies (IIMs) consist of a rare group of autoimmune syndromes characterized by chronic muscle inflammation and muscle weakness. They are classified as autoimmune disorders [1] and have no known cause, research has implicated infectious agents, medications, and ultraviolet radiation in their etiology [2]. Three main types of IIMs have been proposed based on clinical and histopathologic features: (a) polymyositis (PM), (b) dermatomyositis (DM), and (c) sporadic inclusion body myositis (sIBM). Physical therapy is used [9]

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