We report a patient with a testicular teratoma and seminoma, who developed treatment-responsive encephalitis associated with antibodies to NMDA receptor, but not antibodies to Ma2 protein.

A 30-year-old male was admitted to hospital with a 1-week history of personality changes, confusion, agitation and recurrent generalised tonic-clonic seizures. His past medical history was unremarkable, except for the presence of generalised fatigue and sore throat a few days before symptom onset. On physical examination, the only pathological finding was bilateral testicular enlargement. He was agitated and disoriented to time, place and person; his speech was incoherent, and he had persecutory and erotic delusions. The rest of the neurological examination was normal. The initial laboratory studies, including complete blood count, biochemistry, EEG and brain MRI, were normal. The CSF examination was significant for an elevated protein concentration (113 mg/dl) with normal glucose content and mild leukocytosis (25 cells/μl); bacterial and viral studies, including PCR for herpes simplex virus, were negative. Testicular ultrasound revealed the presence of a left testicular mass and right testicular torsion. Computerised tomography of the chest, abdomen and pelvis demonstrated the presence of a retroperitoneal lesion, which was suggestive of metastasis. These findings led us to consider the diagnosis of paraneoplastic encephalitis. Accordingly, CSF …