1) CHOOSE ONE. A 67-year-old woman with bipolar disorder is seen for complaints of poor concentration, racing thoughts, irritability, and sleep disturbance. She has been taking lithium carbonate 600 mg twice daily, and a recent serum lithium level was 0.2 mmol/L. The most likely cause of her current symptoms is:

1. Alzheimer disease
2. Lithium toxicity
3. The bipolar disorder itself
4. An acute stroke