Amyloid myopathy: characteristic features of a still underdiagnosed disease

A 62-year-old man with progressive proximal weakness underwent extensive evaluation including muscle biopsy without a clear diagnosis being established. A repeat muscle biopsy including Congo red-stained sections revealed infiltration of blood-vessel walls and endomysium with amyloid protein, as well as an unusual pattern of pathologic changes to muscle fibers. From a review of 79 cases of amyloid myopathy reported in the English-language literature, the characteristic features of this disorder are described. Congo red-stained sections of muscle biopsy viewed under fluorescent or polarized optics, and serum or urine protein immunoelectrophoresis, play an important role in the evaluation of myopathy. Amyloid myopathy should be a consideration in adults with progressive neuromuscular weakness of uncertain cause.