False Positive Cerebrospinal Fluid NMDA Receptor Antibodies: A Single Center Case Series

Objective To report the presence of CSF NMDA receptor antibodies in four patients without encephalitis encountered at a single tertiary care center. Background The diagnosis and confirmation anti-NMDA relies heavily on detection IgG to NR1 subunit cerebrospinal fluid. While this is generally considered highly specific test for encephalitis, there have been rare reports false positive testing. Design/Methods A retrospective chart review medical records with antibody testing University Texas Southwestern Medical Center between 2011 2021 was performed. Results 40 were identified who had antibodies. Of these patients, 4 (10%) concluded results. results consisted 1 patient refractory status epilepticus from suspected synthetic cannabinoid use, an anaplastic astrocytoma, fungal meningitis Candida dubliniensis, bifrontal cerebritis infectious etiology. testing, 3 immediately recognized as likely positives while misdiagnosed treated autoimmune prior final tissue biopsy. Conclusions Although uncommon, pose significant diagnostic therapeutic challenges clinicians. In our case series, tests occurred apparent central nervous system disorders, including seizure, infection, neoplasm. essential tool caution should be exercised interpreting when clinical paraclinical data are not consistent well characterized phenotype encephalitis.