An Electron Microscope Study of the Ring Fibers and Its Neuromuscular Junction in Human Progressive Muscle Dystrophy

The material was taken at surgical biopsy from the biceps brachial muscle of a 32 years old male with limb-girdle type of muscle dystrophy. The fine structure of the ring fibers in human myotonic dystrophy were studied by electron microscopy. The myofibrils of this fiber were arranged in two different directions: an inner longitudinal and an outer circular group. The circular myofibrils were also interplaced irregularly with a few longitudinal myofibrils. The sarcoplasmic reticulum seemed to be less developed than in normall fibers. Triads occurred irregularly without a definite relationship to the bandings of myofibrils. Mitochondria were seen exclusively in the peripheral sarcoplasm. The neuromuscular junction of the ring fiber corresponded in fine structure to that in the usual skeletal muscle fibers of the fast type, though the secondary synaptic clefts of the muscle fiber appeared more complex.