Broadening the Movement Disorder Spectrum in MECP2 ‐Related Disorders: From Ataxia to Opsoclonus‐Myoclonus

Background MECP2 ‐related disorders encompass a broad spectrum of movement disorders, but opsoclonus has not been characterized within this spectrum. Case Presentation We describe a girl with a de novo pathogenic MECP2 variant who developed an acute/subacute cerebellar presentation following a prolonged febrile illness, evolving from prominent axial ataxia to multifocal myoclonus and opsoclonus. Hyperkinetic manifestations improved with corticosteroid therapy, whereas developmental impairment persisted. Discussion/Conclusion This unusual longitudinal phenotype broadens the recognized movement disorder spectrum in MECP2 ‐related disorders and highlights how an evolving neurogenetic condition may clinically resemble an acquired neuroinflammatory syndrome.