Multiple innervation of muscle fibers in myasthenia gravis

Single fiber EMG recordings from patients with myasthenia gravis obtained during axonal microstimulation revealed an occasional bimodal distribution of response latencies. This phenomenon could be dependent on stimulus strength, however, in a way different from that in the axon reflex. It is suggested to be due to dual neuromuscular junctions (NMJs) supplied by two different motor neurons. Some cases of bimodal jitter were not dependent on stimulus strength and are assumed to be due to dual innervation by the same neuron. The phenomenon could only be demonstrated at abnormal NMJs with partial impulse blocking. It is suggested to reflect multiple reinnervation of muscle fibers that had undergone functional or structural denervation in the course of the immune attack against the original NMJ. This study suggests that the coexisting NMJs from the same or different motor neurons may be functional at the same time.