Correlation of bite force with excitation-contraction coupling time of the masseter in myasthenia gravis.

Abstract

OBJECTIVE:

The aim of this study was to elucidate the relationship between the impairment of excitation-contraction (E-C) coupling of masseter and the bite force in patients with myasthenia gravis (MG).

METHODS:

In 20 patients with MG, masseteric compound muscle action potential (CMAP) and mandibular movement-related potentials (MRP) were recorded simultaneously after stimulating the trigeminal motor nerve with a needle electrode. The E-C coupling time (ECCT) was calculated by the latency difference between CMAP and MRP. Bite force was measured using a pressure-sensitive sheet. Serial assessments of % decrement in masseteric repetitive nerve stimulation (RNS), ECCT, and bite force were performed before and after corticosteroid therapy alone or in various combinations with FK506, cyclosporin A, intravenous immunoglobulin and immunoabsorption.

RESULTS:

Percent amplitude decrement in RNS and ECCT decreased significantly accompanying an increase in bite force after treatment. Simple regression analysis demonstrated a linear correlation among % decrement, ECCT and bite force. However, ECCT shortening accompanying bite force recovery without reduction in % decrement was observed in 4 patients.

CONCLUSIONS:

Masseteric E-C coupling is impaired in some MG patients, and functional recovery of E-C coupling contributes at least in part to the increase in bite force after treatment.

SIGNIFICANCE:

Impaired E-C coupling contributes to muscle weakness in patients with MG.

• Authors: Emiko Tsuda, Tomihiro Imai, Takayoshi Hozuki, Rika Yamauchi, Masaki Saitoh, Shin Hisahara, Hiroaki Yoshikawa, Masakatsu Motomura, Shun Shimohama
• Journal: Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology (Clin Neurophysiol) Vol. 121 Issue 7 Pg. 1051-8 (Jul 2010) ISSN: 1872-8952 [Electronic] Netherlands
• PMID: 20227340 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Topics

• Adult
• Aged
• Bite Force
• Electric Stimulation (methods)
• Excitation Contraction Coupling (physiology)
• Female
• Humans
• Male
• Masseter Muscle (physiology)
• Middle Aged
• Myasthenia Gravis (diagnosis, physiopathology)
• Time Factors
• Trigeminal Nerve (physiology)
• Young Adult