A 28-year-old woman comes to the office because of frequent urination. She urinates approximately every 30 to 60 minutes during the day, which makes it difficult to concentrate at work and attend meetings. She also gets up 1 to 2 times per night to urinate. The patient drinks "a lot of fluid to stay caught up." She says that her 'migraines' have worsened recently and she occasionally feels nauseated. She got a new pair of glasses due to worsening of her vision, which she attributes to spending a lot of time at work. She has had no lower abdominal pain or dysuria.
Her other medical problems include anxiety disorder and knee trauma that she sustained three months ago while jogging. She required arthroscopic surgery and took opioid medications for pain control for two weeks. She has not experienced any knee pain since.
Her BMI is 18 kg/m². Physical examination shows no abnormalities.
Laboratory results are as follows:

Urine pregnancy test is negative. Eight hours following a water deprivation, her weight remains unchanged and her plasma and urine osmolalties are 284 and 650 mOsm/kg H₂O respectively.
Which of the following is the most likely diagnosis?

Question

A 28-year-old woman comes to the office because of frequent urination. She urinates approximately every 30 to 60 minutes during the day, which makes it difficult to concentrate at work and attend meetings. She also gets up 1 to 2 times per night to urinate. The patient drinks "a lot of fluid to stay caught up." She says that her 'migraines' have worsened recently and she occasionally feels nauseated. She got a new pair of glasses due to worsening of her vision, which she attributes to spending a lot of time at work. She has had no lower abdominal pain or dysuria.
Her other medical problems include anxiety disorder and knee trauma that she sustained three months ago while jogging. She required arthroscopic surgery and took opioid medications for pain control for two weeks. She has not experienced any knee pain since.
Her BMI is 18 kg/m². Physical examination shows no abnormalities.
Laboratory results are as follows:

Urine pregnancy test is negative. Eight hours following a water deprivation, her weight remains unchanged and her plasma and urine osmolalties are 284 and 650 mOsm/kg H₂O respectively.
Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec193a_98fe_1af5_853d_a5e4aaf0d902_MD0002_00 This patient presents with polyuria with dilute urine and increased water intake, which is usually due to diabetes insipidus (DI) or primary polydipsia (summarized in the above table). However, the polyuria with water loss is appropriate in polydipsia but inappropriate in DI. Serum Na > 145 mEq/L with a urine osmolality < serum osmolality excludes primary polydipsia and suggests DI. However, patients with an intact thirst mechanism will have adequate water intake to compensate for the water loss and may have a normal sodium level (as in this patient). In cases where a clinical diagnosis is difficult, a water deprivation test should be done to confirm the diagnosis. However, patients suspected of having nephrogenic DI should receive desmopressin without water deprivation and be monitored for a lack of response. water deprivation test This patient is able to concentrate her urine and preserve her plasma osmolality at a normal level in response to observed water deprivation. This suggests that antidiuretic hormone (ADH) release and action are both intact and that the cause of her polyuria is excess fluid intake (primary polydipsia). Her urinary concentration may be subnormal due to chronic water diuresis. (Choice A) Amphetamine abuse can lead to hyponatremia due to increased fluid intake (from hyperthermia) and persistent secretion of ADH that decreases water excretion. This patient's water deprivation test is more consistent with primary polydipsia. (Choice B) Central diabetes insipidus would be associated with weight loss, increasing plasma osmolality (due to renal water loss), and urine osmolality < 300 mOsm/kg in response to water deprivation. (Choice C) Nephrogenic diabetes insipidus would not be associated with an increase in urine osmolality to this level with water deprivation. (Choice E) Chronic diuretic use/abuse is usually associated with hypokalemic alkalosis, which is not present in this patient. Educational objective: Polyuria and polydipsia can be due either to a solute diuresis (usually uncontrolled diabetes mellitus with glycosuria) or a water diuresis. Water diuresis can be due to impaired ADH secretion (central DI), impaired action of ADH on the kidney (nephrogenic DI), or excess fluid intake. The response to controlled/observed water deprivation differentiates among these possibilities. __________ References: Disorders of antidiuretic hormone. (http://www.ncbi.nlm.nih.gov/pubmed/3042388)

A 28-Year-Old Woman Comes to the Office Because of Frequent