Myopathies with abnormal mitochondria: a clinicopathologic classification.

Of 185 patients with myopathy, 22 showed abnormal muscle mitochondria. In 12 of the 22 patients, all of whom had ocular myopathy or the ophthalmoplegia-plus syndrome, muscle biopsies contained 5%-25% "ragged red" fibers. In 4 patients with a facioscapulohumeral distribution of weakness, ragged red fibers were less numerous (3%-8%). In both groups, routine histology showed almost normal muscle. The remaining 6 patients were clinically heterogeneous, all without ptosis or ophthalmoplegia. The biopsies of three of these patients showed severely affected muscle. It is possible that mitochondrial changes in these muscles were nonspecific. Electromyography indicated or suggested a myogenic lesion in 21 of the 22 patients; in 10, the serum creatine kinase was increased.