Patients with myasthenia gravis (MG) who responded to fast-acting treatments including plasmapheresis, high-dose intravenous methylprednisolone, and intravenous immunoglobulin also tended to show improvements in repetitive nerve stimulation amplitude decrements, according to a study published in Clinical & Experimental Neuroimmunology.

Patients who showed a clinical improvement of ≥3 on the quantitative MG (QMG) test or ≥2 on the Myasthenia Gravis Activities of Daily Living scale after fast-acting treatment had statistically higher improvement in amplitude decrement of the proximal muscles tested including the frontalis (P =.004), trapezius (P =.029), and the deltoid (P =.033).

Prior to fast-acting treatment, 23 patients (56%) had abnormal decrement (10% or more) on 1 or more muscles. A higher percentage of patients with generalized MG had an abnormal decrement (60.7%) compared to those with ocular MG (46.2%). After fast-acting treatment, a total of 10 (24.4%) patients showed improvement of abnormal decrement, 9 of which were in the group of patients that showed clinical improvement.

In the subset of patients with generalized MG (n=28), improvement in proximal muscle decrement was significantly greater in the patients with clinical improvement to fast-acting treatment than those who did not improve (46.7% vs 0%; P =.005).

Read more about MG testing

“The changes in amplitude decrements detected by [repetitive nerve stimulation] reflected the therapeutic effect of [fast-acting treatment] in patients with MG, especially among patients with generalized MG compared to those with the ocular type,” the authors said. QMG scores at admission to the hospital (P =.015) and improvement in abnormal repetitive nerve stimulation amplitude decrement (P =.045) were both associated with a response to fast-acting treatment using logistic regression analysis.

“[Repetitive nerve stimulation] responses in the proximal muscles may be potentially useful as an objective measure of improvement after aggressive immunotherapy in patients with MG during hospitalization,” the authors hypothesized.

A total of 41 patients with MG (13 with ocular and 28 with generalized) from Hiroshima City Hiroshima Citizens Hospital in Japan were enrolled in the study. Repetitive nerve stimulation was performed at admission or just prior to fast-acting and again after the completion of fast-acting treatment.

A total of 5 nerve/muscle combinations were tested including the frontalis muscle for the facial nerve, the trapezius muscle for the accessory nerve, the deltoid for the axillary nerve, and the abductor pollicis brevis for the median nerve, and the abductor digiti minimi for the ulnar nerve.

Reference

Naito H, Sugimoto T, Kurokawa K, et al. Changes in the amplitude decremental response to repetitive nerve stimulation following fast‐acting treatment in patients with myasthenia gravis during hospitalization. Clin Exp Neuroimmunol. Published online May 23, 2022. doi:10.1111/cen3.12714