Summary

A 34-year-old woman with a history of relapsing psychosis presented with a 15-month history of impassivity and social withdrawal associated with cognitive impairment. The subsequent recurrence of psychomotor agitation, auditory hallucinations and delusional thinking resulted in an emergency admission under psychiatric services. Initial investigations, including MRI of the brain and cerebrospinal fluid studies were unremarkable and she was treated for a primary psychiatric disorder. The diagnosis of autoimmune limbic encephalitis was established after further investigations revealed the presence of antibodies to the NR1 subunit of the N-Methyl-d-aspartate receptor (NMDAR). Immunotherapy resulted in rapid resolution of psychosis and marked improvement in cognitive and social function. This case underlines the importance of considering anti-NMDAR encephalitis within the differential diagnosis of psychosis associated with cognitive impairment even in those with an apparent previous psychiatric history and response to antipsychotics.