Changes in the amplitude decremental response to repetitive nerve stimulation following fast‐acting treatment in patients with myasthenia gravis during hospitalization

Objectives The aim was to determine the amplitude changes in repetitive nerve stimulation (RNS) decrement values after fast‐acting treatments (FTs), including plasmapheresis, high‐dose intravenous methylprednisolone and intravenous immunoglobulin, in patients with myasthenia gravis (MG). Methods We retrospectively enrolled 41 patients with MG who received RNS after FT. The median, ulnar, facial, accessory and axillary nerves were tested. An improvement in the quantitative MG score of ≥3 or in the MG activities of daily living scale score of ≥2 was used to define clinical improvement posttreatment. A decrement of ≥10% was defined as abnormal. Results Among 41 enrolled patients (ocular type 13 and generalized type 28), 22 (53.7%) showed clinical improvement after treatment. Among generalized MG patients, the proportion of improvement of abnormal RNS decrement in the proximal muscles, including frontalis, trapezius and deltoid, was significantly greater in the group with clinical improvement than in the group without clinical improvement (46.7% vs 0%, P = 0.005). Logistic regression analysis showed that the quantitative myasthenia gravis score at admission and improvement in abnormal amplitude decrement were associated with a response to FT ( P = 0.015 and P = 0.045, respectively). Conclusions The changes in amplitude decrements detected by RNS reflected the therapeutic effect of FT in patients with generalized MG. RNS responses in the proximal muscles might be potentially useful as an objective measure of improvement after aggressive immunotherapy in patients with MG during hospitalization.