Generalized thymoma-associated myasthenia gravis associated with anti-α-amino-3-hydroxy-5-methyl-4 isoxazolepropionic acid receptor antibody encephalitis: A case report.

RATIONALE: Autoimmune neurological disorders, including myasthenia gravis and autoimmune encephalitis, may occur in association with thymoma, warranting careful neurological surveillance. Generalized thymoma-associated myasthenia gravis (g-TAMG) complicated with anti-α-amino-3-hydroxy-5-methyl-4 isoxazolepropionic acid receptor (AMPAR) antibody encephalitis is rare, and its clinical features remain unclear.

PATIENT CONCERNS: A 53-year-old Japanese man was followed up at our department for g-TAMG. The thymoma was classified as B1/B2 mixed according to the World Health Organization classification. He initially developed insomnia, followed by progressive tremors in both upper limbs, dysphagia, and gait disturbance. He subsequently began to experience repeated falls.

DIAGNOSES: Brain magnetic resonance imaging upon admission revealed hyperintense lesions in the extensive cerebral cortex on fluid-attenuated inversion recovery and diffusion-weighted imaging. During this course, serum and cerebrospinal fluid tested positive for AMPAR antibodies, leading to a diagnosis of AMPAR antibody encephalitis.

INTERVENTIONS: Intravenous methylprednisolone pulse therapy, intravenous immunoglobulin therapy, and plasma exchange therapy were administered, followed by rituximab.

OUTCOMES: The neurological prognosis remained poor.

LESSONS: Immunotherapy with rituximab for generalized thymoma-associated myasthenia gravis (g-TAMG) associated with AMPAR antibody encephalitis showed no favorable outcomes. The poor prognosis may have been influenced by the fulminant encephalitis type and residual thymic tumor pathology. Although AMPAR antibody encephalitis is a rare complication of thymoma, its involvement should be considered when patients with thymoma develop central nervous system symptoms.