To discuss the clinical manifestations of five patients with MRI negative Anti-N-methyl-D-aspartate (NMDA) receptor encephalitis at a single healthcare centre 

NMDA receptor encephalitis is characterized by a constellation of neuropsychiatric manifestations associated with IgG antibodies against the NR1 subunit of the NMDA receptors typically detected in CSF through cell-based immunofluorescence assays. Brain MRI is frequently normal in 50-70% of patients.

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This report includes five female patients whose mean age at the time of diagnosis was 30.39 years (range: 20 to 45 years). All five patients presented with psychosis, with three patients experiencing auditory visual hallucinations of a deceased family member. Other notable clinical manifestations were disorganised speech in four patients, dysautonomia in three patients along with catatonia and seizures in two patients. Three patients presented with subacute onset of symptoms and symmetrically brisk reflexes bilaterally. From the cerebrospinal fluid (CSF) analysis data available, oligoclonal bands were found in two patients (n=2), and lymphocytic leukocytosis was seen in three patients (n=5). Anti-NMDA antibodies were positive in the CSF of all patients, while one patient showed serum positivity as well. MRI brain in all patients was negative for medial temporal hyperintensity or hippocampal atrophy. EEG showed epileptogenicity in one patient. All patients received steroids, with additional treatment including Rituximab in 4 patients, IVIg in 3 patients, PLEX and Cyclophosphamide in 2 patients. After extensive evaluation, one patient was detected to have a mature cystic teratoma. Upon follow up, all patients showed improvement in terms of mentation and ability to perform their daily activities. 

NMDA receptor encephalitis remains to be a clinical and antibody based diagnosis. While preliminary evidence suggests that MRI negative patients may have favourable outcomes when compared to those who have hippocampal involvement, further studies are needed to validate the association and determine its prognostication value.