Probable Anti-N-Methyl-D-Aspartate Receptor Encephalitis with Negative Serum Antibodies in an Adolescent Male: Prompt Diagnosis and Long-Term Recovery

Abstract

In addition to a negative antibody test, a delayed availability of antibody test results may postpone treatment. Knowing when to start therapy improves prognosis. The aim of this report was to describe the clinical manifestation and result of early treatment prior to the result of the definitive diagnostic test of anti-NMDAR encephalitis. A 16-year-old previously healthy male was referred from psychiatry due to agitation, incoherent speech, and visual hallucinations, occurring 4 days after a generalized tonic–clonic nonfebrile seizure. The meningeal irritation sign was positive. Blood tests revealed peripheral neutrophilia. Head computed tomography showed cerebral edema and leptomeningeal enhancement (left parietal and bilateral Sylvian fissures), raising suspicion for meningoencephalitis. Electroencephalography (EEG) was normal. Neuropsychiatric symptoms continued despite the antiepileptic and acute psychosis treatment, consistent with probable anti-NMDAR encephalitis. Due to severe agitation, lumbar puncture was not possible, but serum tests for anti-NMDAR antibodies and other autoimmune markers were negative. The patient was treated with high-dose intravenous methylprednisolone and cyclophosphamide. Symptoms improved significantly after the first cycle of cyclophosphamide. The patient resumed school activity after 2 months of cyclophosphamide therapy and was involved in a national competition in a prestigious basketball league after 5 months of therapy. Five years posttherapy, the school and social ability were good, and emotional status was stable. This case emphasizes the importance of clinical diagnostic criteria in suspected anti-NMDAR encephalitis, particularly when confirmatory antibody testing is negative or unavailable. Early recognition and immunotherapy can result in excellent long-term recovery.