Consideration of repetitive nerve stimulation of the median nerve in patients being evaluated for myasthenia gravis

Repetitive nerve stimulation (RNS) of the median nerve is rarely studied in myasthenia gravis (MG). We performed a retrospective analysis of RNS studies performed on 448 patients at our center between 2010 and 2016. Among 95 patients with MG, an abnormal decrement of the compound muscle action potential amplitude was seen in 40.7% of median, 38.4% of spinal accessory, and 57.1% of facial nerve RNS studies. Median nerve RNS was abnormal in 10 patients with normal spinal accessory and 5 patients with normal facial nerve RNS. MG patients with abnormal median nerve RNS were more likely to be seropositive and have limb weakness. No differences were observed in the incidence of abnormal median nerve RNS in patients with and without a median neuropathy at the wrist. Median nerve RNS is easy to perform, reproducible, and should be considered in the electrodiagnostic evaluation of MG.