Clinical reasoning: a woman with subacute progressive confusion and gait instability.

SECTION 1 A 20-year-old healthy woman developed suddenonset, fluctuating gait unsteadiness. She became progressively confused over a 2-week time period and was sent home after she was found wandering the halls of her college dormitory. Her parents noted personality changes and slowed thinking. Several days later she developed a left facial droop and left-sided arm and leg weakness, prompting evaluation at her local emergency department. Vital signs were within normal limits. Neurologic examination was notable for marked abulia and inattentiveness, right lateral end-gaze nystagmus, left hemiparesis, and left-sided dysmetria. She required 2-person assist for ambulation.