A previously healthy 9-year-old girl presents to the emergency department after an episode of generalized shaking, urinary incontinence, and altered mental status. The episode occurred while in school, where she was believed to have fallen asleep until clenching of the fists and shaking were noted. The duration of the episode is unknown. In the emergency department her parents note continued drowsiness, slurred speech, left facial droop, and decreased movement of her left arm and leg. She has no history of seizures. However, her parents state that over the past month she has had fatigue and foot pain, with the appearance of red spots on her distal extremities that had resolved. She has had intermittent sensation of coldness to the left ring finger. There has been no recent travel, fever, or head trauma.

Her vital signs on presentation are as follows: respiratory rate, 24 breaths/min; heart rate, 107 beats/min; blood pressure,...

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