ADEM or MS? How to differentiate between two favored diagnoses

This 15-year-old presents with blurred vision and white-matter lesions on axial FLAIR MRI. Acute disseminated encephalomyelitis (ADEM) and multiple sclerosis (MS) are the two favored diagnoses, so what questions would you ask to differentiate?

You should ask: How long has this symptom been present? Is it clinically monophasic or polyphasic? Was there a recent upper respiratory infection (URI) or vaccination? A longer symptom time favors MS. Monphasic favors ADEM. Polyphasic waxing and waning clinical course favors MS. History of URI, viral infection or recent vaccination favors ADEM. In this case, ADEM is favored due to the patient being an adolescent. Other factors include the extension into the parasagittal genu of the corpus callosum (left greater than right forceps minor). The fact that this is a single monophasic episodic event (blurred vision for two weeks) also favors ADEM.

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