[Muscle biopsy in progressive external ophthalmoplegia (author's transl)].

In skeletal muscle biopsies of nine patients with progressive external ophthalmoplegia of unknown origin "ragged red" fibers can be demonstrated. The occurrence of these abnormal fibers does not correlate with clinical muscle weakness, or additional signs of the ophthalmoplegia plus syndrome. Rarely, "ragged red" fibers are seen in other neuromuscular disorders but usually these are associated with various structural alterations. Numerous "ragged red" fibers in an otherwise normal muscle provide an essential criterion in establishing the diagnosis of the ophthalmoplegia plus syndrome.