Cerebrospinal fluid measurements of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and the dopamine metabolite homovanillic acid (HVA) in samples from 27 children with opsoclonus-myoclonus syndrome and 47 controls are reported from the National Pediatric Myoclonus Center, Children’s Research Institute, Washington, DC, and other centers. The mean age at onset was 1.5 years, and patients were symptomatic for 3 years before evaluation. Treatment with ACTH in 65% of patients had been discontinued for a mean of 27 months before collection of CSF. The etiology was paraneoplastic (46%) or infectious. EEGs were not epileptiform. Concentrations of 5-HIAA and HVA were 30-40% lower in patients compared to controls. Biochemical heterogeneity was evident since low CSF levels of 5-HIAA were not found in all patients with opsoclonus. Lowest values were present in younger patients < 4 years of age, when control values were at their highest, suggesting an impairment of ontogenesis of central serotonergic systems. 
COMMENT. Opsoclonus and myoclonus have been induced by various neurotransmitters and chemicals that alter serotonergic or noradrenergic mechanisms, eg. tricyclic antidepressants, and the chlorinated insecticides, chlordecone and DDT. Low CSF 5-HIAA levels have also been reported in patients with progressive myoclonus epilepsy of the Unverricht-Lundborg type, and other myoclonic disorders.