S12-2. Excitation-contraction coupling in myasthenia gravis: Up to date

Abstract

Although defective neuromuscular transmission is known to be a cause of muscle weakness in myasthenia gravis (MG), previous studies have shown the possible roles of other processes, the failure of which may also cause muscle weakness in MG. Especially, excitation-contraction (E-C) coupling may be defective in patients with MG. Some investigators have applied the post-tetanic potentiation and/or the staircase phenomenon to elucidate the impairment of E-C coupling in MG. Recently, we reported a new method to assess E-C coupling of masseter and abductor pollicis brevis muscles using an accelerometer. In this method, compound muscle action potentials (CMAP) in the belly-tendon fashion and movement-related potentials (MRP) of jaw and finger movements were simultaneously recorded following nerve stimulation. The E-C coupling time (ECCT) was obtained from the difference in onset latencies between CMAP and MRP. The impairment of E-C coupling was assessed by prolonged ECCT and/or low MRP amplitude. In this lecture, I will discuss our data in MG, (1) correlation of bite force with ECCT of the masseter, (2) correlation between anti-ryanodine receptor antibody and ECCT, (3) early effect of tacrolimus in improving ECCT, (4) impairment of post-tetanic potentiation of muscle twitch, (5) effect of local cooling on E-C coupling.