Black and South Asian patients are significantly more likely to develop dermatomyositis than White patients, a large population study has found.

The research, presented at EULAR 2026 by rheumatologist and myositis expert Dr Patrick Gordon of King’s College Hospital, London, identified 4,105 people diagnosed with IIM over 19 years, making it one of the most detailed epidemiological analyses of these conditions to date.

Dr Gordon said the findings offered “much-needed insight into these conditions across the lifespan and among diverse populations.”

Compared with White individuals, dermatomyositis incidence was 54% higher in South Asian patients (aIRR 1.54) and 62% higher in Black patients (aIRR 1.62). Elevated rates were also seen among South Asian, Black and mixed ethnic groups in the broader “other IIM” category.

Sex differences also emerged. Women had higher rates of dermatomyositis and other IIM, while men were more frequently affected by inclusion body myositis (IBM).

A notable finding concerned deprivation and IBM. Patients in the most deprived groups had significantly lower recorded IBM rates than those in the least deprived (aIRR 0.57). The researchers cautioned that it was unclear whether this reflected true biological or environmental differences, or inequalities in diagnosis and access to specialist care.

Overall IIM diagnoses rose substantially over the 19-year study period, but age-standardised rates remained broadly stable, suggesting demographic shifts and population ageing drove most of the increase rather than any true rise in incidence.

The study drew on UK population data and included patients diagnosed with dermatomyositis, IBM or other IIM, a group in which more than half of cases were classified as polymyositis.