CONGENITAL MYASTHENIC SYNDROMES AND MYASTHENIA: P.65Muscular pathological features in Lambert-Eaton myasthenic syndrome

Abstract

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune-mediated disorder of neuromuscular transmission. Voltage-gated calcium channel antibodies (VGCC-Ab) impair calcium influx and acetylcholine release at motor nerve terminals, resulting in the failure of neuromuscular transmission. Patients present with skeletal muscle fluctuating weakness and paralysis in the clinical. Due to LEMS is often misdiagnosed as a peripheral nerve disease or a myopathy, so electromyography (EMG) and muscle biopsy are necessary. The objective of this study was to describe EMG findings and several muscle histology in LEMS. EMG, nerve conduction studies, repetitive nerve EMG showed significantly decreased mean Muscle action potentials (MUP) duration, normal motor and sensory nerve conduction. RNS showed decrease of compound motor action potential (CMAP) amplitude by at least 10% at low-frequency (2-5 Hz) and increased CMAP amplitude by more than 60% at high-frequency (20-50 Hz). Muscle biopsy showed minor evidence of denervation or marked type II fiber atrophy in the patients with longer duration of illness, whereas with shorter duration, there was scattered muscle fiber necrosis. EMG and biopsy abnormalities mimicking myopathy may often be found in patients with LEMS. Rare muscle pathological features associated with LEMS were described.