New myopathy with mitochondrial enzyme hyperactivity. Histochemical demonstration

Abstract

Detailed histo-pathological, histochemical and cytochemical studies were performed on 4 muscle biopsy specimens from 2 patients with progressive proximal and subsequent distal muscle fatigability and weakness during the latter half of the 1st decade of life. In 2 different muscle biopsy specimens from each patient, 50 percent to 60 percent of the muscle fibers having a histochemical type I enzyme pattern contained unusually large mitochondria, characterized by high activities of the oxidative enzymes, and abnormal neutral fat accumulations. The lipid accumulations were thought to reflect an impaired capacity of these mitochondria to oxidize fat. This could be a manifestation of either a structural or an enzymatic mitochondrial abnormality. Positive results of ischemic forearm tests were interpreted as further manifestation of the mitochondrial abnormality in the type I muscle fibers. These cases were compared to other instances of muscle mitochondrial abnormalities described in the literature. Although some were similar, none seemed identical to the abnormalities described herein. This may be a new type of myopathy.