Regeneration in Duchenne muscular dystrophy. Electromyographic evidence

Eight patients with Duchenne muscular dystrophy (DMD) and seven normal children of similar age were studied with a new electromyographic method for coherent displays of potentials. Five hundred motor unit potentials (MUPs) were analyzed in 20 proximal and distal muscles representing a wide spectrum of dystrophy. The progressive MUP disintegration by dropping out of muscle fibers was documented, as well as a high incidence of spontaneous fibrillation. A total of 386 late component (LC) potentials followed the 500 MUPs at consistent latencies. No LC occurred in normal children. The LCs result from motor axon sprouts innervating muscle fibers that are newly formed either by segmentation of existing muscle fibers (focal neucrosis and membrane repair) or by muscle regeneration. Axons in DMD can thus collaterally innervate additional muscle fibers. These processes must delay the onset and progression of clinical weakness in DMD patients.