Lisa Kim is a 19-year-old prenursing student who works part-time in a pediatricians office. Recently, Lisas life seemed to revolve around being close to a bathroom and a drinking fountain. Lisa was urinating every hour (polyuria) and drinking more than 5 L of water daily (polydipsia). She always carried a water bottle with her and drank almost constantly. Lisas employer, a physician, was concerned and wondered whether Lisa had either a psychiatric disorder involving compulsive water drinking (primary polydipsia) or diabetes insipidus. He convinced Lisa to make an appointment with her personal physician. The findings on physical examination were normal. Lisas blood pressure was 105/70, her heart rate was 85 beats/min, and her visual fields were normal. Blood and urine samples were obtained for evaluation (Table 47).

Because of these initial laboratory findings, Lisas physician performed a 2-hr water deprivation test. At the end of the test, Lisas urine osmolarity remained at 70 mOsm/L and her plasma osmolarity increased to 325 mOsm/L. Lisa was then injected subcutaneously with dDAVP (an analogue of arginine vasopressin). After the injection, Lisas urine osmolarity increased to 500 mOsm/L and her plasma osmolarity decreased to 290 mOsm/L. Based on the test results and her response to vasopressin (also called antidiuretic hormone [ADH]), Lisa was diagnosed with central diabetes insipidus. Because she had no history of head injury and subsequent magnetic resonance imaging scans ruled out a brain tumor, Lisas physician concluded that Lisa had developed a form of central diabetes insipidus in which there are circulating antibodies to ADH-secreting neurons. Lisa started treatment with dDAVP nasal spray. She describes the spray as amazing. As long as Lisa uses the nasal spray, her urine output is normal, and she is no longer constantly thirsty.