Abstract
Background/Objectives Anti-NMDA-R antibodies on cerebrospinal fluid (CSF) are a specific test for autoimmune encephalitis. However, false positive results may occur.
Methods A case is described in which CSF anti-NMDA-R antibody testing returned a false positive result, with significant implications for the patient’s course.
Results A 75-year-old male presented with functional decline and low mood following a recent elective laryngectomy for long-term complications after glottic cancer radiotherapy. His medical history included a recent diagnosis of ulcerative colitis, for which he had maintenance vedolizumab and methotrexate. Over 4 weeks he developed worsening mobility, minimal oral intake, new bladder incontinence and confusion. The patient was mute, obeyed 1 stage commands, had severe rigidity in all 4 limbs, and frontal release signs. Initial lumbar puncture demonstrated pleocytosis (Polymorphonuclear cells 126, Mononuclear cells 120), elevated protein (1.79) and low glucose (1.7) with an opening pressure of 5cmH2O. CSF bacterial culture and viral NAT were negative. CSF NMDA-R antibody was positive, using a saline transfer test. MRI showed communicating hydrocephalus and ventriculitis. He was treated with intravenous methylprednisolone, then plasma exchange, without significant improvement. Repeat CSF examination demonstrated an increase in polymorphonuclear cells (699). Subsequently both CSF samples cultured Candida albicans. He was treated with antifungal therapy; however, deteriorated and died. Repeat testing of the CSF sample for NMDA-R antibodies with the porcine brain tissue method was negative.
Conclusion False positive CSF NMDA-R results can have serious consequences. Different methods of testing for NMDA antibodies, including their costs and benefits, require consideration in this context.
