Uncommon presentation of autoimmune limbic encephalitis: a case report

Autoimmune limbic encephalitis is an inflammatory condition of the brain that presents as an acute psychotic disorder. Investigations to confirm this diagnosis often have normal results, and so discriminating between a functional psychiatric presentation and autoimmune neurological disorders can be difficult. In this case report, we present a complex case where multiple repeat investigations were normal and the subsequent diagnosis of autoimmune limbic encephalitis was made due to a strong clinical picture of glutamatergic psychosis that improved with treatment of limbic encephalitis following local guidelines. Traditional investigative findings of autoimmune encephalitis were not present, such as positive findings on magnetic resonance imaging (MRI) of the brain or pelvis, and autoimmune panels to screen for autoimmune antibodies such as anti-NMDA receptor antibodies. The diagnosis and management of this case involved input from a multi-disciplinary team that included internal medicine, neurology, and consult-liaison psychiatry. This case touches on the importance of understanding the clinical picture of autoimmune limbic encephalitis to ensure prompt diagnosis and treatment. Medical students in New Zealand can learn from this case study that, despite best efforts, many tools in medicine have subpar sensitivities and specificities, and that clinical gestalt and experience are necessary when interpreting normal results. This case highlights that autoimmune limbic encephalitis can occur despite normal MRI, EEG, and CSF results, and that early specialist input and empiric immunotherapy should be considered when clinical suspicion remains high.