PLE-2426

A 20-year-old man is brought to the emergency department on a summer day, 20 minutes after developing headache, nausea, and unsteady gait while running the last 2 miles of a marathon. On arrival, he is confused and disoriented. His temperature is 40°C (104°F), blood pressure is 100/60 mm Hg, and pulse is 155/min. His skin is warm and dry. Neurologic examination shows no focal findings. What is the most likely mechanism of this patient’s condition?