[Diagnostic value of muscle biopsy findings in myotonic dystrophy (Curschmann-Steinert) (author's transl)].

By histological, enzyme histochemical, histometrical and ultrastructural studies of 15 muscle biopsies from patients with myotonic dystrophy the typical morphological picture of a myopathy with multiple internal nuclei, sarcoplasmic masses and ring fibers can be shown only in 7 cases with very severe or prolonged clinical course. There is fiber degeneration under the sarcolemma which corresponds to findings in myopathies caused by hypothyroidism. Type-I-fiber-atrophy, which is thought to be an early morphological sign of the disease. can be demonstrated in our material only in proximal muscle groups, especially biceps muscle, whereas tibialis anterior muscle shows a slight focal atrophy of both mean fiber types, which is not helpful for differential diagnosis. Therefore in early cases of myotonic dystrophy which are not clarified by clinical and electromyographic investigation, a biopsy of biceps muscle should be done. Advanced cases as a rule can be confirmed by EMG without muscle biopsy. The morphological differential diagnosis of type-I-fiber-atrophy and the similarities of fiber degeneration under the sarcolemma in myotonic dystrophy as well as in myopathy caused by hypothyroidism are discussed.