Repetitive CMAPs: mechanisms of neural and synaptic genesis

Muscle Nerve. 1996 Sep;19(9):1127-33. doi: 10.1002/(SICI)1097-4598(199609)19:9<1127::AID-MUS7>3.0.CO;2-1.


Repetitive compound muscle action potentials (R-CMAPs) occur when a single nerve shock excites muscle fibers repeatedly. "Double discharges" are due to intramuscular nerve reexcitation. "Synaptic" R-CMAPs, due to excess acetylcholine in the neuromuscular synapse, can occur in congenital myasthenia, the slow-channel syndrome, and acetylcholinesterase inhibition. Secondary nerve excitation can reexcite muscle fibers. Synaptic R-CMAPs in a patient consisted of two discharges. The second diminished during repetitive stimulation and began 3.5-4.0 ms after the first, which is slightly longer than the synapse-muscle refractory period. Neural R-CMAPs, due to ectopic nerve activity, occur in neuromyotonia (NMT). R-CMAPs in a patient consisted of about 20 discharges at 200-300 Hz. Studies in healthy subjects showed that such trains represent added single CMAPs. Impulse frequency in the patient lied close to the threshold of refractoriness. Refractoriness of the synapse-muscle cell assembly determines the characteristics of R-CMAPs regardless of the primary cause.

Publication types

  • Case Reports
  • Review

MeSH terms

  • Action Potentials
  • Adult
  • Autoimmune Diseases / physiopathology
  • Electric Stimulation
  • Female
  • Humans
  • Muscles / physiopathology*
  • Myasthenia Gravis / physiopathology
  • Myotonia / physiopathology
  • Nervous System / physiopathology*
  • Neuromuscular Diseases / physiopathology
  • Synapses / physiology*