A case report of anti-N-methyl-ᴅ-aspartate receptor encephalitis: prioritizing clinical symptoms over diagnostic test results.

Anti-N-methyl-ᴅ-aspartate receptor (NMDAR) encephalitis is the most common type of autoimmune encephalitis; however, the frequently negative initial diagnostic test results for NMDAR complicate its diagnosis. A 40-year-old man with no underlying medical conditions presented with psychiatric symptoms lasting 3 weeks; initial cerebrospinal fluid (CSF) examination, brain magnetic resonance imaging, and electroencephalography findings demonstrated no significant abnormalities. He subsequently developed symptoms characteristic of anti-NMDAR encephalitis, prompting the initiation of immunotherapy before the presence of CSF anti-NMDAR antibodies was confirmed. After receiving intravenous immunoglobulin (IVIG) followed by rituximab therapy, his symptoms improved dramatically. He was discharged 21 days after hospital admission in a healthy condition. The presence of CSF anti-NMDAR antibodies was confirmed post-discharge. This case highlights the importance of maintaining autoimmune encephalitis as a differential diagnosis in cases with similar presentations and in which initial test results identify no abnormalities. In these cases, clinical diagnoses and responses to therapy should supersede diagnostic test findings.