2026 Workshop Handout Bundle-W118J RNS with Clinical Applications

W118J RNS with Clinical Applications - Kesner

Pdf Summary

Repetitive nerve stimulation (RNS) evaluates neuromuscular junction (NMJ) function by measuring changes in compound muscle action potential (CMAP) amplitude during repeated nerve stimulation. Normally, acetylcholine release generates an endplate potential that exceeds the threshold needed to trigger muscle-fiber action potentials. This “safety factor” is reduced in NMJ disorders, so some fibers fail to respond.<br /><br />In postsynaptic myasthenia gravis (MG), acetylcholine-receptor or related antibodies reduce the endplate response. Low-frequency RNS (typically 2–3 Hz) can produce a reproducible CMAP decrement of at least 10%. In presynaptic Lambert-Eaton myasthenic syndrome (LEMS), impaired acetylcholine release causes low baseline CMAPs; rapid stimulation or brief exercise often produces a marked increment, commonly greater than 100%. Botulism may also cause low CMAPs and facilitation, although these findings can be absent, especially in severe cases. Congenital myasthenic syndromes can resemble either presynaptic or postsynaptic disorders; some produce repetitive CMAPs after a single stimulus.<br /><br />Test accuracy depends on careful technique. Patients should generally stop acetylcholinesterase inhibitors for at least 12 hours, and recently botulinum-toxin-injected muscles should be avoided. Adequate limb temperature, stable electrode placement, muscle immobilization, and supramaximal stimulation help prevent false results. Testing should include appropriate muscles, including clinically weak or proximal muscles when indicated; exercise and post-exercise recordings may reveal abnormalities missed at rest.<br /><br />RNS findings must be interpreted alongside nerve-conduction studies, needle EMG, and clinical assessment, since technical problems and other neuromuscular disorders can mimic an abnormal response. Reproducible waveforms, agreement between amplitude and area changes, and documentation of stimulation rate, muscle state, and relevant medication use are important for quality reporting.

Keywords

repetitive nerve stimulation

neuromuscular junction

nmj

compound muscle action potential

myasthenia gravis

Lambert-Eaton myasthenic syndrome

botulism

congenital myasthenic syndromes

acetylcholine receptor antibodies

CMAP decrement

CMAP increment