Atypical myopathy with myofibrillar aggregates.

An autopsy of a 23-year-old woman with progressive muscular weakness and wasting showed a unique muscle abnormality with segmental involvement of individual fibers by peculiar inclusions. Electron microscopically, these inclusions resembled cytoplasmic bodies, being formed of two concentric zones of filamentous materials. They seemed to arise from filaments of myofibrils that were fragmented and highly disorganized in affected areas.