Paraneoplastic opsoclonus myoclonus ataxia syndrome

Abstract

Opsoclonus myoclonus ataxia syndrome (OMAS) is a very infrequent paraneoplastic or postinfectious movement disorder, which may occur at any age, most commonly between 6 and 36 months of age. In four days, a previously healthy 30-month-old girl progressively developed gait instability, intention tremor, dysarthric speech, irritability and altered sleep. Physical and neurological examination did not reveal additional deficits. She had had a transient exanthema without fever three weeks before. Basic blood analysis, serologies, cultures, urine toxin detection, EEG and cerebral CT were normal. Lumbar puncture showed minimal lymphocytosis. On the fifth day following the onset of symptoms, the ataxia worsened, precluding sitting, and the tremor was aggravated by intentional myoclonus. Chaotic saccadic, large amplitude multidirectional but conjugated eye movements appeared. An opsoclonus (OMAS) was suspected and a chest X-ray and CT revealed a paravertebral thoracic mass. Surgery confirmed a localized ganglioneuroblastoma. Blood neuron-specific enolase and urine catecholamine levels were normal. Opsoclonus disappeared with high doses of prednisone and following surgery. Ataxia improved but the patient still required low daily doses of steroids for one year. Conclusions. The diagnosis of OMAS is based on clinical findings. Opsoclonus is a specific clinical sign that all clinicians must recognize. The presence of opsoclonus should always prompt the search for a neural-crest tumour, as one of the most important precipitating causes. The prognosis of this tumour is usually excellent, but neurological symptoms frequently relapse due to the tapering of steroids.