A 43-year-old Caucasian man with a 20-year history of bipolar disorder presents for the first time with long-term polyuria and polydipsia. He previously took lithium for mood stabilization for 15 years before initiating divalproex sodium therapy. He stopped using lithium because of the polyuria, but he felt that the polyuria never fully subsided. His weight is stable, and he has no other urinary complaints. His blood pressure is 115/80 mmHg and his physical exam is normal. His urinalysis shows no blood, cells, protein, glucose, nitrate, casts, or crystals. What is the most likely cause of his polyuria?
1 Central diabetes insipidus
2 Nephrogenic diabetes insipidus
3 Polyuria secondary to hyperglycemia
4 Polyuria following acute kidney injury
5 Polyuria secondary to polydipsia