Severe progression of a young-onset non-paraneoplastic Lambert-Eaton myasthenic syndrome.

The Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare neuromuscular disorder characterized by proximal muscle weakness, hyporeflexia or areflexia, and dysautonomia. Ocular and bulbar symptoms may also occur, though respiratory failure is uncommon; we report the case of a 21-year-old woman diagnosed with LEMS, without evidence of a tumor, who was initially treated with symptomatic medication, immunoglobulin, and steroids, resulting in significant clinical improvement. However, she later developed psychotic symptoms, prompting the discontinuation of steroids. Brain MRI and antineuronal antibody tests were negative. Subsequently, her condition deteriorated, leading to respiratory distress that required urgent intubation, and prolonged dysphagia that necessitated the insertion of a gastrostomy tube for nutrition, along with the maintenance of a tracheostomy. Plasmapheresis was performed, resulting in partial motor recovery. Rituximab was then introduced, leading to sustained improvement in her neuromuscular symptoms, although her neuropsychiatric symptoms persisted; this case highlights a severe progression of young-onset LEMS, marked by prominent bulbar dysfunction and respiratory distress. Neuromuscular improvement followed rituximab treatment, while the concurrent psychotic symptoms appeared to follow an independent course, suggesting a primary psychiatric comorbidity.