5th June 2025

Epidemiology

Dermatomyositis is a rare disease that can occur at any age. Two peaks of incidence have been associated – between 5-15 years old and between 40-60 years old. 

Data on incidence and prevalence is available from a US-population study. The estimated annual incidence of all subtypes is 9.63 per million people, with 13.98 per million in females and 4.68 per million in males. The overall prevalence in all subtypes was estimated at 21.42 in 100,000 people, with 33.09 in 100,000 females and 8.35 in 100,000 in males. 

Juvenile-onset dermatomyositis has an annual incidence of 2-3 cases per million. Females are more commonly affected with the mean age of onset being 10 years old. Adult-onset dermatomyositis affects females more than males, with a ratio of 2.5:1. It is more commonly seen in the black population compared to the white population. Malignancy-associated dermatomyositis affects males and females equally but is more common in over 50s, with risk increasing with age.