Unilateral Task, Bilateral Response: An Acquired Movement Disorder in a Child With Chiari Malformation Type III and Syringomyelia

This teenaged girl with a Chiari malformation type III that was diagnosed and surgically repaired at birth presented with an 8-year history of involuntary movements of the left arm during right-handed tasks (Video 1). These mirrored movements interfered with fine motor skills such as writing, grooming, and dressing. She denied visual changes, nausea, vomiting, or developmental regression. Her neurological examination revealed involuntary left-hand movements during right-hand activity (Video 1), decreased vibratory sensation in her arms and legs, and impaired tandem gait. Magnetic resonance imaging showed a repaired occipital encephalocele, severe untreated ventriculomegaly, and a syrinx extending from C4 to L1 (Figure 1). Mirror movements are involuntary movements that replicate voluntary actions of the contralateral limb and are most often seen in the arms [1]. They represent a type of motor overflow and are considered pathologic when persistent beyond early childhood [2]. Proposed mechanisms include aberrant ipsilateral corticospinal projections, where motor fibers fail to decussate, as well as impaired interhemispheric inhibition, resulting in bilateral cortical activation during unimanual movement [3]. These abnormalities may reflect incomplete development of corticospinal and callosal pathways. Mirror movements are recognized in congenital and midline disorders such as Kallmann and Klippel–Feil syndromes [1, 3, 4] but are rarely reported in association with Chiari malformation type III. This patient underscores the importance of a detailed neurological examination in individuals with congenital hindbrain anomalies and highlights how structural disruption of motor systems may manifest as clinically observable motor overflow. Aysha Arshad: writing – original draft, writing – review and editing, visualization. John R. Crawford: supervision, writing – review and editing, conceptualization, visualization. Written consent was obtained from the parent and patient before submission. John R. Crawford, MD, MS, serves as an associate editor of Annals of the Child Neurology Society.