New estimates of the incidence and prevalence of dermatomyositis (DM) in the US are higher than previously reported, with standard mortality rates three times higher than the general population, according to study results published in Arthritis Care & Research.
Dermatomyositis is an autoimmune disease that causes a rash, inflammation of the muscles, and can lead to muscle weakness. However, the incidence, prevalence, and mortality of DM have not been well studied using established classification criteria.
The current population-based cohort study was conducted to better understand the epidemiology of DM.
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New cases of DM diagnosed between January 1995 and December 2019 using the International Classification of Diseases (ICD) codes 9 or 10 have been identified. Each case was manually screened for DM using the European Alliance of Associations for Rheumatology / American College of Rheumatology (EULAR / ACR) 2017 DM classification criteria, a specialist diagnosis, and Bohan & Peter 1975 criteria.
The researchers calculated the incidence and prevalence (as of January 1, 2015) that were age- and sex-adjusted for the US, non-Hispanic, white population of 2000. Standardized mortality rates were calculated by comparing the survival of the DM cohort with the expected survival rates.
A total of 40 cases of incident DM were identified, which were confirmed by 1 of the 3 criteria; 29 patients lived in Olmstead County. Of these, 26 (90%) were women and 12 (41%) had clinically amyopathic DM (a form of DM without muscle weakness). The median follow-up was 8.2 years.
The adjusted total incidence of DM was 1.1 per 100,000 person-years (95% CI, 0.7-1.5 per 100,000 person-years), which corresponds to 2,858 new DM cases each year in the United States. The prevalence of DM was 13 per 100,000 person-years (95% CI, 6-19 per 100,000 person-years), which corresponds to 34,061 people with DM in the United States. The standardized mortality rate for people with DM was significantly higher than expected (3.1; 95% CI, 1.1–6.8), but not for people with clinically amyopathic DM (1.1; 95% CI, 0.2 -3.3). The positive predictive value of 2 or more ICD 9 or 10 DM codes for validated DM was 40 out of 82 (49%).
The limitations of the study included the limited geographic region, which lacked racial and ethnic diversity; reliance on clinically diagnosed DM, which may have excluded mild cases of DM; potentially inconsistent documentation of DM characteristics by different providers; missing antibody data for early DM cases; a small sample size; and the exclusion of patients with juvenile DM.
The researchers concluded, “This population-based study, using validated DM criteria, found the incidence and prevalence at the high end of previous reports and significantly increased mortality from myopathic DM compared to peers. Future, larger studies of validated DM cases should investigate the incidence and mortality over time as well as causes of death in order to better understand the pathogenesis and treatment of the disease. “
Disclosure: Some study authors stated links with biotech, pharmaceutical, and / or device manufacturers. For a full list of specifications, see the original reference.
reference
Kronzer VL, Kimbrough BA, Crowson CS, Davis III JM, Holmqvist M, Ernste FC. Incidence, prevalence, and mortality of dermatomyositis: a population-based cohort study. Arthritis Care Res. Published online September 21, 2021. doi: 10.1002 / ACR.24786
This article originally appeared on Rheumatology Advisor
