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

A review of the article by Smoyer-Tomic et al., ‘Incidence and prevalence of idiopathic inflammatory myopathies among commercially insured, Medicare supplemental insured, and Medicaid enrolled populations: an administrative claims analysis'

Introduction

Autoimmune idiopathic inflammatory myopathies (IIMs) have the following common characteristics: Auto-immune disorder, no known cause, muscle inflammation, and muscle weakness and consist of three types: polymyositis, dermatomyositis, and sporadic inclusion body myositis. Many studies have not examined IIM, however using data gathered from commercial insurance, Medicaid and Medicare, this study examined how common and frequent IIM is.

Methods

Data from 2004 - 2008 was gathered from:

1. 130 unique commercial insurance companies for outpatient pharmacy claims for people under 65 (14 million enrollees annually)
2. Medicare supplemental insurance paid for by employers for retired and working-age recipients (1.6 million individuals)
3. Pooled Medicaid healthcare information from 10 states (28 million)

The data was filtered for patients over the age of 18 with an IIM treatment and patients who had a muscle biopsy; incidence and prevalence was then calculated.

Results

The study identified 2,990 incident cases with 2,477 (83%) were from the commercially insured/Medicare supplemental databases and 513 (17%) were from the Medicaid database with 1,072 had dermatomyositis, 1,784 had polymyositis, and .476 had interstitial myositis. The study also identified 7,155 prevalent patients 39.1% had dermatomyositis, 58.9% had polymyositis, and 9.8% had interstitial myositis.

Discussion

The data showed that IIM incidence for 2004–2008 for commercial/ Medicare supplemental groups was 4.27 cases per 100,000 py, and 5.23 cases per 100,000 py for Medicaid, with the highest incidence among the polymyositis type (2.46 commercial/Medicare supplemental and 3.53 Medicaid new cases per 100,000 py). Overall, the study shows that in the U.S., IIM incidence will likely range from 3 to 7 new cases per 100,000 py and prevalence for IIM treatment will range from 32,000 to 68,000 per year.