Repetitive nerve stimulation is a variant of the nerve conduction study where electrical stimulation is delivered to a motor nerve repeatedly several times per second. By observing the change in the muscle electrical response (CMAP) after several stimulations, a physician can assess for the presence of a neuromuscular junction disease and differentiate between presynaptic and postsynaptic conditions.
Repetitive nerve stimulation is used to diagnose neuromuscular junction (NMJ) disorders, the most common of which is myasthenia gravis. A decremental response (a smaller and smaller muscle response with each repetitive stimulus) is abnormal and indicates NMJ dysfunction. This can be further confirmed if the response normalizes after administration of edrophonium or neostigmine
As with all nerve conduction studies, the body part tested should be clean, free of lotions and conductive substances, with jewellery removed.
It is best to advise patients to refrain from taking acetylcholinesterase inhibitors (e.g., Pyridostigmine / Mestinon) for 6–8 hours before the study, unless medically contraindicated. These agents make more ACH available to bind at the ACHRs and may potentially diminished CMAP decrement, resulting in a normal study (false negative).
A peripheral nerve is electrically stimulated, and the amplitude of the CMAP is recorded at rest and after a short voluntary activation. The stimulation frequency is 3 Hz, the number of stimuli 10. The result is reported as the difference in amplitude of the CMAP between stimulation one and four (in %). The area value changes typically in parallel, but is not reported. If there is a major difference between amplitude and area decrement, technical factors should be considered.
