Clinical Reasoning: A young woman with symmetric weakness and behavioral disturbance.

A 19-year-old woman presented with altered mental status and progressive quadriparesis. One week prior to admission, she experienced headaches and behavior changes, including social withdrawal and a fixation on electronics. The day prior to admission, she developed weakness in both arms, and was unable to lift them above her head, followed shortly thereafter by proximal leg weakness and difficulty climbing stairs. The next day, she was intermittently unresponsive and unable to stand without assistance. Her medical history was notable for supraventricular tachycardia and depression. She was on an estrogen-containing oral contraceptive and fluvoxamine, which had been started for depression 6 weeks prior to admission. She had also recently completed a course of amoxicillin for bronchitis. She had no pertinent family history. Her social history was significant for IV heroin use approximately 2 months prior to admission. Her initial examination was notable for disorientation to time and place and impaired concentration and short term memory, with intact language and cranial nerves. There was 2/5 strength in both her arms and legs, with preserved sensation to light touch and vibration, and 2+ reflexes, although a Babinski sign was present bilaterally.