Inclusion body myositis (IBM). Morphological study.

Among the chronic idiopathic inflammatory myopathies inclusion body myositis (IBM) has emerged as a clinicopathologic variant. Slowly progressive weakness of the distal and the proximal muscle groups, the presence of rimmed vacuoles with basophilic granules as well as 15-18-nm filamentous inclusions in affected muscle confirm the clinical and histopathological distinction between inclusion body myositis and chronic polymyositis.