A 27-year-old woman had a 2 month history of progressive headache, nausea, vomiting and deterioration in memory, mood and affect. She was 5 months post partum. Prior to her admission to hospital, her symptoms were attributed to post-partum depression. She had no significant medical history. Her only medication at admission was citalopram, which was recently started by her family physician because of her deteriorating mood and labile affect.

On examination, her vital signs were normal. She was alert and oriented. Formal cognitive testing revealed difficulty with attention, concentration and short term memory. Constructional and …