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 login to view 2 more bullets Epidemiology Incidence login to view 1 more bullet 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 login to view 18 more bullets Imaging MRI brain with and without gadolinium login to view 2 more bullets Studies Lumbar puncture login to view 1 more bullet Differential Multiple sclerosis (MS) login to view 3 more bullets Treatment Medical login to view 3 more bullets Complications Severe neurological impairment