A new type of progressive muscular dystrophy, autosomal recessive distal muscular dystrophy, is described, based on observations on 17 cases (8 males and 9 females) in 8 families, including an autopsied case. The disease developed in young adults. Muscle weakness and atrophy were most marked in the distal parts of the legs, especially in the gastrocnemius and soleus muscles, and then spread to the thighs and gluteal muscles. Early impairment of standing on tip-toe with retention of the ability to stand on the heels was conspicuous. Difficulty in climbing stairs, standing up and walking subsequently appeared, but rarely progressed to confinement to bed. The forearms became mildly atrophic, with decrease in grip strength, but the small hand muscles were spared. The EMG showed myopathic changes and nerve conduction was normal. Serum creatine kinase activity was characteristically increased up to 100-fold in the early stages of the disease. It was also markedly increased in subjects in the preclinical stage and mildly in some heterozygotes. Muscle biopsies revealed myopathic changes with severe segmental necrosis accompanied by regeneration. The changes were similar to those of Duchenne muscular dystrophy. An autopsied case, aged 68 years, showed generalized muscle abnormalities with a distal predominance. The muscles in the lower legs, especially those of the calves, were severely affected. No lesions were found in the brain, spinal cord or peripheral nerves.
Histopathological changes induced by the intramuscular injection of glycerol were studied in the muscle fibers of rabbits. Fifteen minutes after the injection of 1 ml of 50% (v/v) glycerol, hypercontraction of fibers, disruption of the plasma membrane, and invasion of lanthanum into the sarcoplasm were observed. Between 12 and 24 h after the injection, more extensive pathological changes were seen which included: variation in fiber size; degeneration and necrosis of muscle fibers; hypercontraction of fibers by light microscopy; disruption of the plasma membrane by electron microscopy; vacuolar changes; hypercontraction of myofibrils, and selective loss of Z-bands. Between 7 and 14 days after glycerol injection, extensive regenerative changes were seen. The degenerative changes were similar to those seen in muscle in Duchenne muscular dystrophy, suggesting that a similar mechanism may be involved in the two conditions, so that experimental glycerol myopathy could be a good model for pathophysiological studies on Duchenne muscular dystrophy.
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