Adult-onset mixed myopathy with nemaline rods, minicores, and central cores: a muscle disorder mimicking polymyositis.

A woman, aged 75 years, presented with a 15-year history of progressive, generalized, painful muscle weakness and wasting. Clinical and laboratory investigation revealed a sporadic muscle disorder. Muscle biopsy showed a mixed pattern of nemaline myopathy with minicores and central cores and severe atrophy of type-1 and type-2 fibers. A trial of immunosuppressive treatment did not improve her condition, which clinically mimicked chronic progressive polymyositis. Mixed myofibrillar myopathies of this type have so far only been described among the group of congenital myopathies.