Snapshot A 8-year-old boy presents to the pediatric emergency department for altered mental status. One day prior to presentation he reported a headache with mild lower extremity weakness. He also developed nausea and 2 episodes of nonbloody, nonbilious emesis. Of note, he developed a viral illness approximately 2 weeks ago. On physical examination, the patient is oriented to self but not to time or location. He has left-sided lower extremity weakness and hyperreflexia in the affected limb. A CT scan of the brain demonstrates mild hypodense white matter lesions. A lumbar puncture demonstrates a lymphocytic lymphocytosis with mildly elevated protein. After he was stabilized, an MRI brain and spine demonstrated hyperintense white matter lesions. Introduction Definition an autoimmune demyelinating disease affecting the central nervous system commonly triggered by viral infections Epidemiology Incidence most common in children (especially) and adolescents Etiology Viral infections Vaccinations (less common) Pathogenesis An environmental stimuli (e.g., infection) in a genetically susceptible host leads to an autoimmune response against the central nervous system Presentation Symptoms/physical exam nonspecific signs headache fever nausea vomiting encephalopathy altered mental status irritability and confusion psychosis somnolence/coma other neurological deficits oculomotor deficits dysarthria sensory changes seizures aphasia optic neuritis meningismus Imaging MRI brain with and without gadolinium indication imaging modality of choice in stabilized patients Studies Lumbar puncture mild lymphocytic pleocytosis with mildly elevated protein is suggestive of ADEM Differential Multiple sclerosis (MS) differentiating factors ADEM typically follows a viral illnes while MS usually does not MS presents with recurrent attacks separated by time and space Treatment Medical high-dose intravenous corticosteroids (e.g., methylprednisolone) indication first-line treatment for ADEM Complications Severe neurological impairment