CSF studies which ultimately led to the possible diagnosis of anti-NMDAR encephalitis.

A 17-year-old man with no significant medical history presented with new-onset seizure activity and altered mental status manifesting as bizarre behaviour, which included rapid pressured and tangential speech, psychomotor agitation, insomnia and delusions. He also had autonomic dysregulation, manifested in labile blood pressures. He had been recently discharged from his first psychiatric hospitalisation. Many studies were performed, including electroencephalogram (EEG), head CT, laboratory work, urine drug screen and lumbar puncture with cerebral spinal fluid studies, which ultimately led to the diagnosis of anti-N-methyl-D-aspartate receptor (NMDAR) autoimmune encephalitis. He was treated with five rounds of plasmapheresis with complete resolution of his altered mental status. This case highlights the importance of being familiar with the presentation of anti-NMDAR autoimmune encephalitis, especially in cases of new-onset mental status changes with psychotic like symptoms, seizure-like activity and autonomic dysregulation as early detection and treatment improves chances of good prognosis with return to baseline cognitive function. © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.