Document Type: Original Article

Authors

1 Department of Geriatric Medicine, Ziaeian Hospital, Tehran University of Medical Sciences, Tehran, Iran Memory and Behavioral Neurology Division, Roozbeh Hospital, Tehran University of Medical Sciences, Tehran, Iran

2 Department of Neurology, Shariati Hospital, Neuromuscular Research Center, Tehran University of Medical Sciences, Tehran, Iran

3 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Sina Trauma and Surgery Research Center, Tehran University of Medical Sciences, Tehran, Iran

4 Department of Dermatology, School of Medicine, Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran

5 Department of Cardiology, School of Medicine, Qazvin University of Medical Sciences, Qazvin, Iran

Abstract

Background: Myasthenia gravis (MG) affects the neuromuscular transmission, causing fluctuating muscle weakness and fatigue. This study is carried out with the aim to study the electrophysiologic findings of different subtypes of MG referred to our center in Tehran, Iran.
Methods: All patients with MG presenting to neurology department of Shariati Hospital, Tehran University of Medical Sciences were enrolled. Clinically, patients with MG were categorized as ocular vs. generalized. The acetylcholine receptor (Ach-R) and muscle-specific receptor tyrosine kinase (anti-MuSK) antibodies were performed. Repetitive Nerve Stimulation (RNS) was performed using the standard method, with supramaximal stimulation of muscles at the 3 Hz frequency by surface electrode at rest. Abductor pollicis brevis (APB) (median nerve), anconeus (radial nerve), trapezius (accessory nerve), and nasalis (facial nerve) muscles were studied in all patients. Single fiber electromyography (SFEMG) was performed by standard method.
Results: 196 seropositive patients with MG were included in the study. In electrophysiological studies, RNS was performed for 146 patients of Ach-R-Ab positive MG, with positive results in 110 patients. In addition, SFEMG was conducted for 8 patients with negative RNS, which resulted in 7 positive tests. 
Among 23 patients with anti-MuSK-positive MG, RNS was performed for 16 patients, with positive results in 11 patients. The 5 remaining patients with negative RNS test were studied by SFEMG, 4 of whom had positive results. APB compound muscle action potential (CMAP) decrementation significantly correlated with Ach-R-Ab positive MG (P < 0.03).
Conclusion: This finding can support the hypothesis that the selection of muscles in electrodignostic study would be important. The electrodiagnostic studies are a good and non-invasive diagnostic tool for MG, and a combination of different distal, proximal, and facial muscles can increase the overall sensitivity of the test.

Keywords

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