Opsoclonus Myoclonus Syndrome/Dancing Eye Syndrome (OMS/DES) in Children With and Without Neuroblastoma (NBpos and NBneg)Opsoclonus Myoclonus Syndrome/Dancing Eye Syndrome (OMS/DES) in Children With and Without Neuroblastoma (NBpos and NBneg)

Inclusion Criteria: * Children with newly diagnosed OMS/DES either NB-pos or NB-neg. Three out of the following four components are necessary for the diagnosis of OMS/DES: * Opsoclonus or ocular flutter (but not nystagmus) * Ataxia and/or myoclonus * Behavioural change and/or sleep disturbance * Neuroblastoma The diagnosis of OMS/DES may be difficult in some patients. Opsoclonus, in particular, may be intermittent or late in onset. A video example will be available at www.dancingeyes.org.uk. If uncertain, please contact the national coordinator for support in interpreting clinical features. * Age 6 months or over up to less than 8 years (\< 8th birthday) The date of diagnosis of OMS/DES is the date on which a doctor confirms the condition to be OMS/DES. The date of symptom onset needs also to be documented. * Treatment start with the standard corticosteroid treatment with dexamethasone pulses as proposed by the guidelines given in this trial protocol (see 11.10, page 71). * In patients with presumed NB-neg OMS/DES, neuroblastoma must be excluded according the guidelines of this trial (see chapter 4.4.1.4, page 30, and appendix 11.9, page 70) * Documented informed consent for treatment and enrolment in the trial by parents / legal representatives. Exclusion Criteria: •Patients with opsoclonus, myoclonus or ataxia caused by other identified disease (e.g. current active CNS infection, neurometabolic disorder or demyelination). An identified viral precursor is not an exclusion criterion. * prior or parallel use of chemotherapy (other than required for treatment of the neuroblastoma) * Corticoid steroid for OMS/DES or other reasons lasting 14 days or more immediately before treatment start according the standard treatment proposed (treatment with corticosteroids for less than 14 days will be allowed) * contre-indication of use of one of the experimental study drug (cf Summary of Product Characteristics used in this study)