2026 Workshop Handout Bundle-W271 - Repetitive Nerve Stimulation

W271 - Repetitive Nerve Stimulation - Harrison

Pdf Summary

The workshop reviews the physiology, performance, and interpretation of repetitive nerve stimulation (RNS) for disorders of neuromuscular transmission.<br /><br />At the neuromuscular junction, nerve impulses trigger acetylcholine (ACh) release, producing an end-plate potential that normally exceeds the threshold needed to activate muscle fibers. This reserve is the “safety factor.” Reduced safety factor causes some fibers to fail to fire, lowering compound muscle action potential (CMAP) amplitude during repeated stimulation.<br /><br />In myasthenia gravis (MG), postsynaptic antibodies impair ACh receptors or their organization, typically producing a decrement during slow RNS. Lambert-Eaton myasthenic syndrome (LEMS) and botulism impair presynaptic ACh release; both may cause low baseline CMAPs and increased responses after exercise or rapid stimulation. Botulism’s electrodiagnostic findings can be incomplete, so their absence does not rule it out.<br /><br />Accurate testing requires supramaximal stimulation, stable electrode placement, muscle immobilization, adequate limb temperature, and review of both CMAP amplitude and area to identify artifacts. Slow RNS generally uses 2–3 Hz stimulation. A decrement of about 10% between the first and fourth responses is commonly considered abnormal. In MG, brief maximal exercise may temporarily improve a decrement; prolonged exercise may reveal delayed exhaustion. In suspected LEMS, a post-exercise CMAP increment is useful, with a 60% increase potentially significant when suspicion remains despite not reaching 100%.<br /><br />Test selection matters: proximal and facial muscles improve sensitivity, particularly in generalized or MuSK-antibody-positive MG. Sensitivity is lower in ocular MG and when only distal muscles are tested. RNS results should be interpreted alongside clinical findings, antibody status, routine nerve conduction studies, and, when needed, single-fiber EMG.<br /><br />Reports should document stimulation rate and number, muscle state, calculation method for decrement or increment, and relevant medication timing, and should include waveforms when possible.

Keywords

repetitive nerve stimulation

neuromuscular transmission

myasthenia gravis

Lambert-Eaton myasthenic syndrome

botulism

compound muscle action potential

safety factor

acetylcholine release

decrement response

single-fiber EMG