Diagnostic Sensitivity of Repetitive Nerve Stimulation Test on Individual Muscles Analysis of 357 Cases with Myasthenia Gravis

J Korean Assoc EMG Electrodiagn Med 1999;1(2):150-155.
Published online May 9, 1999.

Abstract

Objectives : Repetitive nerve stimulation test(RNST) is a useful tool for the diagnosis of myasthenia gravis(MG). It is known that the diagnostic sensitivity is higher in proximal muscles than distal and increased by doing the test on many muscles. To clarify the diagnostic sensitivity on each tested muscle is important for the effort-effect relationship. Methods : We analyzed data of RNST performed on 5 muscles(abductor digiti quinti, flexor carpi ulnaris, orbicularis oculi, nasalis and trapezius muscles) of 357 MG patients(129 with only ocular symptoms and 228 with generalized symptoms). Results : The overall sensitivity of RNST in MG was 69.7% with higher positive rate in patients with generalized symptoms(86.4%) than with ocular symptoms only(40.3%). The sensitivity was greater in proximal muscles(orbicularis oculi 59.5%; nasalis 54.5%; trapezius 46.4%) rather than distal ones(flexor carpi ulnaris 34.4%; abductor digiti quinti 28.2%). However, RNST on one or two muscles was not good enough and several muscles had to be tested to increase the diagnostic sensitivity. Conclusions : The following sequence of RNST may be helpful on the aspect of effort-effect relationship for the diagnosis of MG; Ulnar nerve with 2 muscles(flexor carpi ulnaris and abductor digiti quinti) followed by facial nerve with 2 muscles(orbicularis oculi and nasalis), then accessory nerve on trapezius muscle.

Key Words: Repetitive nerve stimulation test, Myasthenia gravis