ACETYLCHOLINE-RECEPTOR ANTIBODIES IN THE LAMBERT-EATON MYASTHENIC SYNDROME

Two patients were initially diagnosed with myasthenia gravis with elev ated titers of acetylcholine receptor antibodies. Features including w eakness that normalized with sustained contraction, areflexia, autonom ic symptoms, and low-amplitude baseline compound muscle action potenti als with abnormal increments following brief exercise and high-frequen cy repetitive stimulation, however, suggested that these patients had Lambert-Eaton myasthenic syndrome. One patient had antibodies directed against presynaptic calcium channels, confirming the diagnosis. The s econd patient was seronegative for these antibodies but had elevated t iters of antistriated muscle antibodies. This shows that serologic stu dies can conflict with clinical and electrodiagnostic findings in pati ents with Lambert-Eaton syndrome. These cases also point out that acet ylcholine receptor antibodies are not necessarily diagnostic of myasth enia gravis in patients with Lambert-Eaton syndrome. Instead, these an tibodies could represent a nonpathogenic epiphenomenon.