Epidemiology and diagnostic challenges of anti-NMDAR encephalitis: a study from the Waikato region.

Aims: Anti-NMDAR encephalitis is an increasingly recognised autoimmune disorder, with evolving diagnostic criteria. This study aims to analyse the prevalence and diagnostic patterns of anti-NMDAR encephalitis in a New Zealand hospital setting.

Methods: Data from Waikato Hospital's lab database, encompassing anti-NMDAR antibody requests between August 2013 and July 2023, were examined. Cases were categorised based on age, gender and diagnostic outcomes.

Results: In all requests, 288/318 (91%) were processed and 10/288 (3.5%) anti-NMDAR antibodies were positive. Positive cases were equally frequent by sex, with an average age of 29.4 years. Only 6/10 were diagnosed with anti-NMDAR encephalitis, while others received alternative diagnoses. Māori ethnicity was overrepresented. This study indicates a low prevalence of anti-NMDAR encephalitis in the Waikato region, with adult predominance. Ethnic disparities were observed. The need for refining testing criteria to optimise cost-effectiveness is discussed.

Conclusion: Anti-NMDAR encephalitis is relatively rare in Waikato Hospital, New Zealand, with diagnostic challenges related to testing criteria and ethnic diversity. Further research and consideration of testing protocols are warranted.