Clinical Reasoning: A 7-year-Old Boy with Acute Onset Altered Mental Status.

A 7-year-old boy presented with acute-onset headache, vomiting, and confusion during summer. Two months previously, he developed right thigh pain, causing intermittent limping. Three days before admission, he developed headache; 1 day later, he experienced fatigue, nausea, and vomiting. On the day of presentation, symptoms included behavioral change (showered 15 times), unsteadiness, and new palmoplantar rash. He presented with confusion and lethargy and was transferred to our facility. His father had a recent gastrointestinal illness, but there were no other sick contacts. There were no recent weight changes, fever, tick/animal exposure, or travel. Past medical history included prior herpes simplex virus (HSV)–positive facial lesion (at 5 years old). The patient took no medications, had no known allergies, was developmentally normal, and was appropriately vaccinated. On general examination, he was somnolent and irritable, and had a palpable right thigh mass and palmar/solar petechiae. Neurologically, he was arousable to light touch, followed only simple midline commands, answered yes/no to orientation questions and responded to all naming questions with “I don't know.” Cranial nerves were intact. He had normal muscle bulk/tone and at least 3/5 strength throughout, but encephalopathy limited assessment. He had normal sensation to light touch and muscle stretch reflexes, neutral plantar responses, and no dysmetria. The patient sat in bed independently but refused to stand or walk.