[Laryngopharyngeal characteristics of myasthenia gravis].

OBJECTIVE

To observe the laryngopharynx manifestation and electromyography characteristics of myasthenia gravis (MG) patients.

METHODS

Thirty cases of MG were included in this study, their laryngopharynx symptoms and signs, voice acoustic assessment, laryngeal electromyography (LEMG) behaviors and repetitive nerve stimulation test(RNS) were analyzed, and the data was compared with that of normal subjects.

RESULTS

About 36.7% of MG patients (11/30) had the symptoms of hoarseness, voice fatigue, dysphonia and dysphagia. The vocal folds movements of 16.7% of MG patients(5/30) appeared weaker than normal, and their vocal glottic couldn't close completely, while with a seam during phonation. Voice amplitude (68.3 +/- 14.6) dB (x +/- s, same at below), and maximum phonation time (15.1 +/- 4.0) s, were greatly lower than normal; shimmer(2. 43 +/- 1.19)%, and normalized noise energy (-9.6 +/- 3.3) dB, were greatly higher than normal. The amplitudes of interference patterns in MG patients' LEMG markedly decreased, except introarytenoid muscle, during low, normal and high pitch phonation, the amplitudes of thyoiarytenoid muscle were (215 +/- 69) microV, (298 +/- 113) microV and (380 +/- 153) microV, those of cricoarytenoid muscle were (253 +/- 92) microV, (361 +/- 116) microV and (486 +/- 155) RV. The turns increased but had no statistical difference. In the RNS test, 83.3% MG patients (25/30) showed masculine response. There were about 2.20 +/- 1.32 pieces of laryngeal muscles involved, and the reduction rate in amplitude of the compound muscle action potential for RNS was about (27.9 +/- 19.2)%.

CONCLUSIONS

Only parts of MG patients had laryngopharyngeal symptoms, but the laryngeal muscles of most of them were involved, appearing as the masculine response for RNS, the decreased synchronization of the laryngeal muscles' interference patterns, the decreased capacity of phonation. MG must be differentiated when a patient has the symptoms of voice weakness, hoarseness and dysphonia. Laryngeal RNS test should be used in the early diagnosis of MG.