Lambert-Eaton myasthenia syndrome: specified description of a response pattern to low-frequency repetitive nerve stimulation

Abstract

Objective: We aimed to specify and quantify the characteristics of the decrement in low-frequency repetitive nerve stimulation response in Lambert-Eaton myasthenia syndrome (LEMS) and compare it to those of myasthenia gravis (MG).

Patients and methods: We retrospectively reviewed 18 patients with LEMS and 24 patients with MG. Ten consecutive stimulations were applied at 3 Hz to the abductor pollicis brevis. We determined the position of the smallest wave in the stimulation sequence, and we calculated the decrement and recovery.

Results: The median sequential order of the minimum wave was 8 in the LEMS group and 5 in the MG group (p < 0.001). The median decrement in the LEMS group was 36.7%, while that in the MG group was 21.0% (p = 0.047). The recovery percentage was 1.4% in the LEMS group and 3.5% in the MG group (p = 0.001). The area under the curve for the sequential order of the minimum wave was 0.90, and the reciprocal optimum cut-off point was 6.5.

Conclusions: We elucidated a pattern with a delayed nadir and subsequent poor recovery, featuring a low-frequency decrement; furthermore, we determined the most likely sequential order of the minimum wave in patients with LEMS, and the indicator was useful for differentiation.

Keywords: Electrophysiology; Lambert-Eaton myasthenia syndrome; Low-frequency decrement; Myasthenia gravis; Neuromuscular disorder; Repetitive nerve stimulation.