EMG Phenomena of Peripheral Axonal Hyperexcitability

In needle electromyography (EMG), phenomena of increased excitability of muscle fibers and motor axons are important for the diagnosis of neuromuscular diseases. Motor axonal hyperexcitability includes spontaneous phenomena such as fasciculations, spontaneous continuous motor unit single discharges (SCMUSDs), myokymia, neuromyotonic serial discharges and crampi. It also includes stimulus-induced phenomena such as some A-waves, stimulus-induced complex repetitive discharges or tetanic spasms in electrolyte disturbances. In the present review, the state of knowledge on the various phenomena of motor axonal hyperexcitability is reported. One focus is on SCMUSDs as a new member of the group of spontaneous potentials from the motor axon.