Clinical and Autoimmune Profiles of Omani Patients with True Versus False Positive Autoimmune Encephalitis Antibodies Panels

The incidence of autoimmune encephalitis (AE) is rising due to increased awareness of the condition and detection of new autoantibodies. Coinciding with this rise are false positive autoantibodies without clinical correlates. Objective: To explore the clinical profiles of Omani patients who are truly positive for AE autoantibodies and compare them with those with false-positive autoantibodies. Methods: We reviewed the medical records of all patients who tested positive for AE antibody from May 2016 to December 2022. Cases were verified by three neurologists based on the existing criteria for AE. Results: The participants comprised N = 67 patients, 19 (28%) of whom fulfilled the criteria for AE. True-positive AE patients were younger with mean age of 35.3 ± 4.7 years (p = 0.010). They were also more likely to present with subacute memory disturbances (6/19; 32%; p = 0.030), seizures (12; 63%; p = 0.028), abnormal electroencephalogram (EEG) findings (10; 65%; p = 0.040), and abnormal signals in limbic region on magnetic resonance imaging (MRI) (5; 26%; p = 0.010). Subacute memory disturbance was a significant predictor for true positivity (OR = 17.807, 95%CI = 1.608–197.202; p = 0.019). Anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis was the most frequent type of AE (8; 42.1%), followed by anti-glutamic acid decarboxylase 65 (GAD65) (4; 21.1%). Conclusion: Of the 67 cases with positive AE autoantibody panel, 48 (72%) were false-positive. The presence of subacute memory impairment was a significant predictor of AE. Anti-NMDAR encephalitis was the most frequent AE encountered in our cohort.