Diagnosis and classification of sporadic inclusion body myositis (sIBM).

Sporadic inclusion body myositis (sIBM) is the most common acquired muscle disease in elderly individuals, particularly men. Its prevalence varies among ethnic groups but is estimated at 35 per one million people over 50. Genetic as well as environmental factors and autoimmune processes might both have a role in its pathogenesis. Unlike other inflammatory myopathies, sIBM causes very slowly progressive muscular weakness and atrophy, having a distinctive pattern of muscle involvement and different forms of clinical presentation. In some cases a primary autoimmune disease coexists. Diagnosis is suspected on clinical grounds and is established by typical muscle pathology. As a rule sIBM is refractory to conventional forms of immunotherapy.