Plasma Exchange-Responsive Bulbar Dysfunction in Thymoma-Associated Myasthenia Gravis with Concomitant Lambert-Eaton Myasthenic Syndrome.

The coexistence of thymoma-associated myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome (LEMS) is rare, and no established therapeutic strategy exists for this condition. We herein report a case of MG-LEMS overlap syndrome (MLOS) in which plasma exchange (PE) effectively treated severe bulbar dysfunction refractory to intravenous immunoglobulin (IVIg). Sequential electrophysiological testing demonstrated an improvement in the low compound muscle action potential amplitudes and post-exercise increments, reflecting LEMS activity. This case highlights that PE may be more efficacious than IVIg for bulbar symptoms in MLOS, particularly with prominent presynaptic involvement, and supports electrophysiological assessment to guide treatment.