Opsoclonus–myoclonus due to underlying ganglioneuroblastoma

Imaging description A 19-month-old child presented with symptoms of difficulty in walking, abnormal eye and limb movements, and irritability. MRI of the brain for suspected cerebellar ataxia was unremarkable (Fig. 16.1a, b). CT scan of the neck and chest revealed a small left paraspinal soft tissue lesion at the level of T1 and T2 (Fig. 16.1c–e) and a diagnosis of neuroblastoma-associated opsoclonus–myoclonus syndrome (OMS) was suggested. Metaiodobenzylguanidine scintigraphy (MIBG) scan was negative (Fig. 16.1f). Excision biopsy of the mass confirmed the diagnosis of a ganglioneuroblastoma. Importance OMS, also known as dancing eye syndrome, is a rare disorder that presents in early childhood with involuntary rapid eye movements, myoclonic limb jerking, ataxia, and behavioral changes. It can be idiopathic, postinfectious, or a paraneoplastic manifestation of neuroblastoma. OMS is associated with neuroblastoma in 40% of patients and occurs between the ages of six months and three years in these patients. Conversely, only about 2% of patients with neuroblastoma present with OMS. In children, OMS may occur as a paraneoplastic manifestation of all neural crest tumors, including neuroblastoma, ganglioneuroblastoma, and ganglioneuroma. The pathogenesis of OMS is thought to be immune-mediated, with a cross-reactive autoimmunity between neuroblastoma cells and the central nervous system. Neuroblastomas associated with OMS tend to be low grade, thoracic in location, and have a more favorable outcome than non-OMS neuroblastomas. Neuroblastomas associated with OMS are usually very small in size and present a diagnostic challenge as they are less metabolically active and urinary catecholamines or MIBG scans can be negative. CT and/or MRI of the neck, chest, abdomen, and pelvis are the most sensitive studies to detect these occult neuroblastomas (Fig. 16.1).