Science News: Epidemiology and Natural History of Inclusion Body Myositis A 40-Year Population-Based Study

Submitted by: Niranjan Singh, MD, DM

Shelly S, Mielke MM, Mandrekar J, et al. Epidemiology and natural history of inclusion body myositis: A 40-year population-based study. Neurology. 2021;96(21):e2653-e2661. doi:10.1212/WNL.0000000000012004

Summary: This study determines the prevalence and natural history of sporadic inclusion body myositis (sIBM) and tests the hypothesis that patients with sIBM have higher cancer or mortality rates than the general population. The study identified 20 patients (10 clinicopathologically defined, 9 clinically defined, and 1 probable) according to the ENMC criteria and 1 patient with all features of clinicopathologically defined sIBM except for symptom onset at <45 years of age. The prevalence of sIBM in 2010 was 18.20 per 100,000 people ≥50 years old. The incidence of cancers in sIBM did not differ from that observed in the general population. Two-thirds of patients developed dysphagia, and half required a feeding tube. Nine patients required a wheelchair. The median time from symptom onset to wheelchair dependence was 10.5 (range 1–29) years. Overall life expectancy was shorter in the sIBM group compared to the general population (84.1 vs 87.5). Thirteen patients died; 9 deaths were sIBM related (7 respiratory and 2 unspecified sIBM complications). Female sex and dysphagia were independent predictors of death.

In summary, autoimmune diseases, especially rheumatoid arthritis, were common in this population (48% with an autoimmune disease). Statin therapy is well tolerated among patients. The risk of cancer did not increase in sIBM. Patients with sIBM have a slightly shorter life expectancy compared to general population, especially in female patients, patients with dysphagia, or those with symptom onset after 67 years.

Comments: This is one of the longest observational studies of sIBM. Several important observations are made compared to the general population. Risk of cancer did not increase. Statin therapy, sometimes a concern in patients with muscle disease, is well tolerated. Female sex, presence of dysphagia, and symptom onset after 67 years were poor prognostic factors.