Isolated orofacial dystonia and facial pain as the inaugural manifestation of anti-NMDAR encephalitis: a case report and literature review.

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis typically presents with psychiatric symptoms, seizures, and cognitive dysfunction. Movement disorders, when present, usually coexist with these features. We report a rare case of anti-NMDAR encephalitis in a 30-year-old female who presented with isolated left temporomandibular joint (TMJ) dystonia, jaw tremor, and facial pain as the sole manifestations for seven months, without clinically significant psychiatric, cognitive, or seizure symptoms. The patient was repeatedly misdiagnosed with TMJ disorder and muscular dysfunction before anti-NMDAR IgG antibodies were detected by cell-based assay (CBA) in serum (1:32) and cerebrospinal fluid (CSF, 1:1). First-line immunotherapy with intravenous immunoglobulin (IVIG) achieved remission. However, she relapsed five months later following COVID-19 infection, with antibody titers rising to 1:100 in both serum and CSF. High-dose corticosteroid pulse therapy and maintenance mycophenolate mofetil were administered, achieving sustained clinical improvement over four years of follow-up, although mild residual focal dystonia persisted. Whole-exome sequencing and hereditary ataxia screening excluded genetic causes. This case broadens the clinical spectrum of anti-NMDAR encephalitis and underscores the importance of early antibody testing in young patients with treatment-refractory orofacial movement disorders.