To the Editor We read with interest the study by Armangué and colleagues1 about the clinical and immunological features of opsoclonus-myoclonus syndrome (OMS). Opsoclonus-myoclonus syndrome is a rare movement disorder characterized by involuntary saccades, limb myoclonus, and cerebellar ataxia.2 Its etiology is idiopathic or paraneoplastic (P-OMS). The authors retrospectively investigated a large case series of 114 adult patients with OMS, with the aim of identifying possible clinical clues or antibody biomarkers that could differentiate idiopathic OMS from P-OMS. They found that older age and encephalopathy were significantly associated with P-OMS.