52. Repetitive stimulation and Lambert–Eaton myasthenic syndrome

Abstract

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease with antibodies against voltage-controlled calcium channels (antiVGCC). The etiology can be paraneoplastic or idiopathic. Clinically, the patients have paresis of proximal muscle in the limbs, hyporeflexia, ptosis, fatigue, and autonomic symptoms. Electromyography is essential for diagnosis. The initial amplitude of the compound muscle action potential (CMAP) is strikingly low and is increased after facilitation. Low frequency repetitive nerve stimulation (LFS) 2–5 Hz shows decrement of amplitude and high frequency repetitive nerve stimulation (HFS) 20–50 Hz shows increment (increment over 100% is diagnostic for LEMS). The aim of the presentation is to share the electrophysiological findings in our three patients. Age of patients (females) were 30–57 years, the development of their disease was 0.2–4 years, all of them had positive antiVGCC type P/Q. One patient had a paraneoplastic form. If we stimulated abductor digiti minimi muscle (ADM), we found that the initial amplitude of CMAP was low in only one patient. LFS 3 Hz showed a decrement of at least 10% just in one patient and HFS 30 Hz showed increment 40%, 67% and 600% in these patients. If we stimulated abductor hallucis muscle (AH), the initial amplitude of CMAP was low only in one patient, LFS 3 Hz showed decrement of more than 10% in two patients and the HFS 30 Hz showed increment 117%, 136% and 200% in these patients. We consider that AH should be always investigated by HFS 30 Hz, where we constantly recorded increment over 100% in contrast to the stimulation of ADM.