Prevalence of sporadic inclusion body myositis in Western Australia.

A 10-year retrospective review was conducted to ascertain the prevalence of inclusion body myositis (IBM) in Western Australia. Seventeen patients with sporadic IBM aged 45-90 years were identified and the prevalence of IBM was calculated to be 9.3 x 10(-6). The prevalence was higher in men (10.9 x 10(-6)) than in women (7.7 x 10(-6)). The mean age of onset of IBM was 56.6 years, and the mean delay between onset of symptoms and diagnosis was 4.4 years. The age-adjusted prevalence over the age of 50 years was 35.3 x 10(-6). The results suggest a higher prevalence of IBM than has previously been reported.