Myoclonic encephalopathy of infants or "dancing eyes syndrome". Report of 7 cases with long-term follow-up and review of the literature (cases with and without neuroblastoma).

We describe 7 children with myoclonic encephalopathy of infants (MEI). MEI is a clinical entity characterized by an acute or subacute onset of polymyoclonia, cerebellar ataxia and opsoclonus ("dancing eyes"). It occurs either spontaneously, following an infectiuos illness or in association with an occult neuroblastoma. It is likely that immunological factors play a role in the pathogenesis. Steroid therapy resulted in rapid dramatic improvement of the neurological symptoms in 4 cases. However, this initial response did not correlate with the eventual outcome. We reviewed the literature to compare 45 reported cases of MEI associated with a neuroblastoma with 48 children without such a tumor to identify possible differences in clinical presentation, response to steroid medication and long-term prognosis of the neurological syndrome. In this respect we found no differences. Impairment of motor, verbal or intellectual performance were reported in at least half the cases. Although an immediate and marked response to steroids occurs in many cases of both groups, it remains unclear whether the long-term outcome is favourably influenced by this medication. The two-year-survival rate (90%) in the neuroblastoma group and the percentage of mediastinal localisation of the tumor (49%) are much higher compared with neuroblastomas without MEI. The reasons for these remarkable differences are not known. Diagnostic, therapeutic and prognostic implications justify the separation of MEI from the more common and benign syndrome known as acute cerebellar ataxia of childhood.