A 34-year-old man develops excessive thirst and frequent urination while being hospitalized for multiple injuries following a motorcycle collision. His urinary osmolality after 4 hours of water restriction is 250 mOsm/L and increases to 700 mOsm/L after administration of antidiuretic hormone. The patient is started on an appropriate medication, and his symptoms promptly resolve. Over the next 2 years, multiple attempts are made to wean the patient off the medication, but his symptoms would always return, necessitating the resumption of treatment. The permanence of this patient's condition is best explained by traumatic damage to which of the following structures?

Question

A 34-year-old man develops excessive thirst and frequent urination while being hospitalized for multiple injuries following a motorcycle collision.  His urinary osmolality after 4 hours of water restriction is 250 mOsm/L and increases to 700 mOsm/L after administration of antidiuretic hormone.  The patient is started on an appropriate medication, and his symptoms promptly resolve.  Over the next 2 years, multiple attempts are made to wean the patient off the medication, but his symptoms would always return, necessitating the resumption of treatment.  The permanence of this patient's condition is best explained by traumatic damage to which of the following structures?

Quizplus · Accepted Answer

11ec160b_3571_46cd_9249_a9bdfff117c7_MD0001_00 This patient has diabetes insipidus (DI), a condition that results in the production of large volumes of very dilute urine due to impaired antidiuretic hormone (ADH) activity. DI can be due to deficient ADH production in the brain (central) or resistance to ADH in the kidneys (nephrogenic). Injection of exogenous ADH can help distinguish between central and nephrogenic DI: ADH administration substantially increases urine osmolality in patients with central DI, whereas patients with nephrogenic DI typically have a more limited increase in urine osmolality (<300 mOsm/L increase). ADH is synthesized by magnocellular neurosecretory cells in the paraventricular and supraoptic nuclei of the hypothalamus. These neurons project axons to the posterior pituitary where axon terminals store large quantities of ADH for later release into the circulation. Injury to the hypothalamus or posterior pituitary (eg, head trauma, transsphenoidal neurosurgery, suprasellar masses) can result in central DI. Damage to the more distal portions of the hypothalamic-hypophyseal tract (ie, below the infundibulum) typically causes transient DI because the cell bodies of the magnocellular neurons remain intact. However, hypothalamic injury results in death of the magnocellular neurons, causing permanent central DI. (Choice A) The anterior pituitary produces ACTH, TSH, gonadotrophic hormones, prolactin, and growth hormone. Hormone secretion from the anterior pituitary is regulated by substances released from the median eminence into the hypothalamic-hypophyseal portal vessels. (Choice C) Although head trauma is a frequent cause of central DI, traumatic damage to the kidneys does not result in nephrogenic DI. Furthermore, this patient's large increase in urine concentration following ADH administration is more suggestive of central DI. (Choice D) Isolated posterior pituitary damage most often causes transient central DI because the cell bodies of the magnocellular neurons remain intact and can undergo axonal regeneration to allow adequate ADH release into the circulation. (Choice E) Thalamic nuclei are involved in relaying sensory and motor signals to the cerebral cortex and in regulating alertness and consciousness. Educational objective: Injury to the hypothalamus or posterior pituitary (eg, head trauma, transsphenoidal neurosurgery, suprasellar masses) can result in central diabetes insipidus (DI). Damage to the posterior pituitary gland typically causes transient DI, whereas damage to the hypothalamic nuclei often causes permanent DI. __________ References: Diabetes Insipidus after Traumatic Brain Injury (http://www.ncbi.nlm.nih.gov/pubmed/26239685)

A 34-Year-Old Man Develops Excessive Thirst and Frequent Urination While