Occult cartilaginous choristoma in a child with myelin oligodendrocyte glycoprotein antibody-associated encephalomyelitis.

Myelin oligodendrocyte glycoprotein antibody-associated disease is a central inflammatory demyelinating disorder that cause diverse neurological symptoms. Paraneoplastic neurologic syndromes occur in association with malignant neoplasms and manifest with a wide range of neuropsychiatric symptoms. Paraneoplastic neurological syndrome is rare in myelin oligodendrocyte glycoprotein antibody-associated disease and, when reported, is typically seen in adults. Herein, we report a 3-year-old girl who presented with lower limb paralysis, urinary retention, and seropositivity for myelin oligodendrocyte glycoprotein antibody. Her symptoms did not respond to various immunotherapies. She was incidentally found to have a cartilaginous choristoma in the neck, after surgical resection of which, she showed symptomatic recovery without recurrence. Immunohistochemical analysis of the resected tumor revealed expression of myelin oligodendrocyte glycoprotein within the cartilage tissue. Based on this case experience, children presenting with myelin oligodendrocyte glycoprotein antibody-associated disease who fail to respond to immunotherapies may need prompt screening for occult tumors.