[Selective muscle fiber type anomalies in neuromusclar disorders. An analysis of 124 consecutive muscle biopsies (author's transl)].

The following parameters were measured and calculated in 124 consecutive muscle biopsies: mean fiber diameter, standard deviation, percentage of type I and Type II fibers, variability coefficient, hypertrophy and atrophy factor. Twenty percent of the histometrically analyzed biopsies showed a type II atrophy and four percent a type I atrophy. Type II atrophy was found particularly in the following disorders: collagen vascular diseases, steroid myopathies, cachexia and as a result of inactivity. Some neurogenic processes also demonstrated a selective type II atrophy. The combination of a grouped type II atrophy with a type I hypertrophy is characteristic of chronic and usually heredodegenerative disorders of the motoneurons. The presence of a selective type II atrophy argues against a genetically determined muscular dystrophy. A mixed atrophy classified here as strong or very strong primarily suggests a neuropathy. A selective type I hypertrophy has been found exclusively in neurogenic processes, and type II hypertrophy predominantly in the cases of chronic heredodegenerative neurogenic and primarily myopathic diseases. An increase of the variability coefficient of both types of muscle fibers is more frequent and pronounced in neurogenic processes than in myopathic syndromes. Type II fibers show a selective increase in the variability coefficient considerably more often than type I fibers. In contrast to other reports we seldom found a fiber type predominance or a pathological type-grouping. Only two out of five biopsies with pathological fiber type-grouping were definitely neurogenic. In special cases the histometric analysis of muscle fiber types improves the diagnostic efficiency of muscle biopsies.