Neuromuscular Junction Disorders (NMJ) O-NJ001. Electrodiagnostics profile in Myasthenia gravis

Abstract

Introduction . Repetitive Nerve Stimulation (RNS) has a sensitivity of 50-80% in predicting Myasthenia Gravis (MG). This wide range is affected by type and severity of MG, muscle tested, frequency of stimulation and exercise. There has been a previous study describing these factors but did not confirmed it with the result of Single Fiber (SF) and Acetylcholine Receptor antibody (AChR). Methods . This was a cross-sectional study. Data was from RNS results of MG patients in Electromyography laboratories, Cipto Mangunkusumo National Hospital January to December 2019. Muscle tested on RNS were abductor digiti minimi (ADM) muscle, trapezius (Tr) muscle and orbicularis occuli (OrbOc) muscle. Slow RNS used 3, 5, 7 and 10 Hz stimulation followed by 3 Hz stimulation immediate, 1 minute (min) and 2 min post exercise. Decrease of Compound Muscles Action Potential (CMAP) amplitude > 10% is considered as positive RNS. Results . As much as 47 patients were included in this study. The average age of patients is 43 years old. As much as 44.7% had a positive RNS test, and 70% of the case was positive from OrbOc, followed by Tr (60%) and ADM (30%). Frequency of stimulation that obtained the positivity the most is at 5 Hz, and the 4th wave revealed the lowest point of decreament, followed by the 5th wave. Single Fiber was positive in 57.4% of the case, and AChR was positive in 51.1%. There are 11 patients (23.4%) that has a mismatch results between SF and AChR. Conclusion . RNS without confirmation of SF and AChR may yield a false negative result. Orbicularis Oculi shows the most sensitive muscle tested in RNS, with stimulation of 5 Hz and the 4th waveform the lowest decrement. SF and AChR are still important in confirming strong suspicion patients with MG despite negative results in RNS.