Diagnosis and treatment for Lambert–Eaton myasthenic syndrome

Abstract

Lambert–Eaton myasthenic syndrome (LEMS) is a neuroimmunological disorder characterized by impaired acetylcholine release from presynaptic terminals that can lead to limb weakness, decreased tendon reflex, autonomic symptoms, and cerebellar ataxia. The lesion is located at the neuromuscular junction. As is well known, small cell lung cancer is a feature of this syndrome and is recognized as one of the paraneoplastic neurological syndromes with malignant coexistence in more than 50% of patients. Autoantibodies to P/Q–type voltage–gated calcium channels localized to presynaptic terminals are known to occur in 90% of LEMS patients. From an epidemiological perspective, LEMS is not a frequent disease. In Japan, the number of patients with LEMS was estimated to be 348 (as of 2017), with an estimated prevalence of 0.27 per 100,000 population. However, because it is an infrequent disease, it is crucial to ensure its diagnosis, and the first step in treatment for LEMS is its accurate diagnosis, which was emphasized in the “Myasthenia Gravis/Lambert-Eaton Myasthenia Syndrome Clinical Practice Guidelines (edited by Japanese Society of Neurology)” published in 2022. Clinical and research issues or recent topics in LEMS include

・ Immune targets and immunological mechanisms

・ Mechanisms of autonomic dysfunction development

・ Association with paraneoplastic cerebellar degeneration

・ LEMS and immune checkpoint inhibitors : should we be aware of side effects or use them for treatment?

・ An old and new treatment for LEMS : amifampridine

This review outlines the old and new issues in LEMS.