The clinical features of published case series of acute disseminated encephalomyelitis (ADEM) and multiple sclerosis (MS) are reviewed at the Institute of Neurology, Queen Square, London. Differences in presentation of the two disorders may help in the early diagnosis, in the absence of a reliable diagnostic test for MS. Monophasic ADEM is more common in children <10 years old whereas MS usually presents at >10 years, and only 2.7-4.4% of cases of MS occur under 16 years of age. A precipitating infection is common in ADEM and unusual in MS. ADEM presents with signs of encephalopathy or encephalitis (headache, vomiting, drowsiness, meningism, and seizures in 13-35%), but these symptoms are uncommon in MS. Optic neuritis is bilateral in ADEM and unilateral in MS. CSF shows increased protein and lymphocytosis in ADEM, and oligoclonal bands in MS. Both ADEM and MS show disseminated inflammatory demyelinative lesions on brain MRI; these are cortical and in deep grey matter in ADEM and periventricular/callosal lesions in MS. Follow-up MRI shows no new lesions in ADEM, and relapse with additional lesions after 6 months in MS. 
COMMENT. The differentiating factors for ADEM and MS outlined above are useful when considered as a group of presenting characteristics, but individually their value is limited. In an analysis of initial MRI findings predictive of a second attack of acute CNS inflammatory demyelination in 116 children, Mikaeloff et al found that the risk of MS was significantly higher in patients with corpus callosal lesions, whereas basal ganglia lesions were equally frequent in monophasic (ADEM) and recurrent (MS) disease (Ped Neur Briefs 2004;18:65-66) . Tenembaum et al (2002) found relapses and MS in 10% cases initially diagnosed as ADEM; residual disability was not related to MRI findings at onset, but it was correlated with the occurrence of optic neuritis (Ped Neur Briefs 2002;16:81).