Long duration between presentation of probable anti-N-methyl-D-aspartate receptor encephalitis and either clinical relapse or positive serum autoantibodies.

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is an autoimmune encephalitis first described in 2007. This condition has a well-characterised clinical phenotype with a multistage presentation beginning with prodromal symptoms, psychosis, cognitive deficits, and seizures, which can progress to involve movement disorders, catatonia, autonomic instability, and central hypoventilation requiring ventilatory support. Our first patient demonstrates, to our knowledge, the longest duration between the presentation of anti-NMDAR encephalitis and clinical relapse that has thus far been described. Our second patient highlights a clinical scenario where positive serum autoantibodies are demonstrated six years following complete clinical recovery, in the absence of clinical features of a relapse or a malignancy on screening. These patients highlight the importance of long-term follow up and tumour surveillance, and the role of electroconvulsive therapy in the management of catatonia. These cases also support the need for future studies evaluating the role of maintenance immunosuppression in patients at high risk for relapses.