Repetitive nerve stimulation: Relative muscles sensitivity in generalized myasthenia gravis

• Published in: Neurophysiologie clinique Vol. 48; no. 4; p. 249
• Main Authors: Zouari, Rania, Hdiji, Olfa, Kacem, Hanen Haj, Bouattour, Nadia, Farhat, Nouha, Sakka, Salma, Dammak, Mariem, Mhiri, Chokri
• Format: Journal Article
• Language: English
• Published: Paris Elsevier Masson SAS 01-09-2018; Elsevier Science Ltd
• Subjects: Acetylcholine receptors; Cholinesterase; Diagnosis; Electromyography; Facial nerve; Immunoglobulins; Muscles; Myasthenia; Myasthenia gravis; Nerves; Neurology; Neuromuscular junctions; Repetitive nerve stimulation; Thymus; Repetitive nerve stimulation; Electromyography; Myasthenia gravis
• ISSN: 0987-7053; 1769-7131
• DOI: 10.1016/j.neucli.2018.06.077

The diagnosis of myasthenia gravis (MG) is established through the medical history and examination and confirmed by the clinical response to anti-cholinesterase medication, the detection of anti-acetylcholine receptor antibodies (AchR) and especially electrodiagnostic testing using repetitive nerve stimulation (RNS) [3]. However, the sensitivity of RNS depends on the distribution of clinically affected muscles and its severity [2]. We aimed to investigate the decrement of RNS of various muscles in patients with generalized MG in order to test the nerve-muscle sensitivity.
We performed a retrospective study of patients with clinical diagnosis of MG, who attended our neurology department [2011–2018] (n:33) and we included those with generalized MG to investigate their neurophysiological outcomes. All patients had a neurological examination. Patients who have not a detailed neurophysiological study including RNS within these 3 spots (facial-nerve, accessory-nerve, upper limbs nerves) were excluded.
Among the 33 patients with MG, we selected 27 patients (M/F:8/19) who had generalized MG with fluctuating motor weakness and oculo-bulbar involvement. Their age ranged from 14 to 77 years (mean, 47.77 years) and the average age at onset was 44.18 years. Forty-four percent had thymus abnormality and 83.33% had positive antibody testing to AchR. RNS studies showed at least one abnormal muscle response (significant decrement>10% in low frequencies) in 96.29%. Decrement was most detected in the facial nerve (77.77%). An abnormal trapezius response was observed in 55.55%. However, hand muscles abnormalities tested using the ulnar, medial and radial nerves stimulation were detected respectively in 48.14%, 37.03% and 14.81%. The facial nerve was significantly more sensitive than any other nerve (P<0.05) in patients with generalized MG.
RNS is a commonly used technique to evaluate patients with MG, through multiple nerve-muscle testing [1]. Therefore, the facial nerve seems to be the most sensitive one.