Question

A 37-year-old woman suffers a severe head injury in a skiing accident. Shortly thereafter, she becomes polydipsic and polyuric. Her urine osmolarity is 75 mOsm/L, and her serum osmolarity is 305 mOsm/L. Treatment with 1-deamino-8-D-arginine vasopressin (dDAVP) causes an increase in her urine osmolarity to 450 mOsm/L. Which diagnosis is correct? 1) Primary polydipsia 2) Central diabetes insipidus 3) Nephrogenic diabetes insipidus 4) Water deprivation 5) Syndrome of inappropriate antidiuretic hormone (SIADH)

Answer 1

The correct diagnosis is central diabetes insipidus, indicated by low urine osmolarity and a positive response to dDAVP, which confirms a deficiency in the production or secretion of ADH by the posterior pituitary gland.

Step-by-step explanation:

The correct diagnosis for a 37-year-old woman who suffers from polydipsia and polyuria following a severe head injury, along with a response to dDAVP that increases urine osmolarity from 75 mOsm/L to 450 mOsm/L, is central diabetes insipidus.

Central diabetes insipidus is caused by a deficiency in the production or secretion of antidiuretic hormone (ADH), also known as vasopressin, which is normally released from the posterior pituitary gland. The woman's initial low urine osmolarity indicates that the kidneys are failing to concentrate urine, which is a typical feature of diabetes insipidus. The serum osmolarity of 305 mOsm/L suggests that her body fluids are more concentrated than normal, which triggers thirst and leads to the consumption of large volumes of water (polydipsia).

The administration of dDAVP, a synthetic analogue of ADH, increases the permeability of the renal collecting ducts to water, which leads to an increase in urine osmolarity, as observed in this case. This confirms that the kidneys can respond to ADH and points to a deficiency in ADH production or secretion by the pituitary as the underlying problem, characterizing central diabetes insipidus.

Learn more about Central Diabetes Insipidus