A Rare Case of Coexisting Psychogenic Polydipsia and Nephrogenic Diabetes Insipidus With Lithium Therapy.

Lithium is a commonly used medication for mood stabilization and a well-known cause of nephrogenic diabetes insipidus (DI). Coexistent psychogenic polydipsia with nephrogenic DI is uncommon, and its management is challenging due to the wide variation in serum sodium based on fluctuations in water intake. Here, we describe the case of a 56-year-old male with psychogenic polydipsia and nephrogenic DI which manifested in wide swings of serum sodium over a short interval. He initially presented with hyponatremia with low urine osmolality consistent with psychogenic polydipsia. His serum sodium began to improve after free water restriction. However, later in the course, he developed an increase in serum sodium levels and polyuria with persistent low urine osmolality consistent with DI.