The 7-year-old boy now in your office was last seen 2 weeks ago with a mild viral upper respiratory tract infection. Today, however, he presents with fever, ataxia, weakness, headache, and emesis. In the office, he has a 3-minute left-sided tonic-clonic seizure. You send him to the hospital and order a magnetic resonance imaging (MRI) with contrast of the brain, the results of which are shown. This boy's likely diagnosis is which of the following?

(b) Source: (Hay et al, p 755. Kliegman et al, pp 2079-2080. McMilla et al, p 2263. Rudolph et al, p 920.) ADEM is an autoimmune demy-elinating disease seen in children less than 10 years of age. It may follow many different types of infections, including upper respiratory tract infections, varicella, mycoplasma, herpes simplex virus, rubella, rubeola, and mumps; it may also follow immunizations. The MRI presented in the question shows multiple "white" plaques scattered across the brain representing areas of demyelination. The history and physical examination findings of ADEM are similar to multiple sclerosis; differences include age of onset (ADEM is usually seen in < 10-year olds), the presence of systemic findings like fever and emesis, and the lack of progression in the lesions once identified. Mortality is high, with 10% to 30% of affected patients dying. Treatment is high-dose corticosteroids. Meningitis is not usually diagnosed with MRI, but rather a lumbar puncture. Malignancies and neurocysticer-cosis (CNS infection by the tapeworm Taenia solium) do not present with the MRI findings described.