DIABETES INSIPIDUS Flashcards
A 35-year-old patient presents with excessive thirst, urinary frequency, and nocturia. Laboratory tests reveal a 24-hour urine volume of 50 mL/kg and a urine osmolarity of 270 mosm/L. Which of the following is the most likely diagnosis?
A. Primary polydipsia
B. Nephrogenic diabetes insipidus
C. Central diabetes insipidus
D. SIADH
Correct Answer: C. Central diabetes insipidus
Rationale: Central DI is characterized by a deficiency in AVP secretion, leading to large volumes of dilute urine (urine osmolarity < 280 mosm/L). The symptoms of thirst, urinary frequency, and nocturia align with the diagnosis.
Which of the following is NOT a cause of nephrogenic diabetes insipidus?
A. Lithium toxicity
B. Hypokalemia
C. Multiple sclerosis
D. Genetic mutations affecting AVP receptors
Correct Answer: C. Multiple sclerosis
Rationale: Multiple sclerosis is associated with dipsogenic DI (a subtype of primary polydipsia) due to inappropriate thirst. Nephrogenic DI results from renal insensitivity to AVP caused by factors such as lithium toxicity, hypokalemia, or genetic mutations.
Which laboratory finding is consistent with SIADH?
A. Hyperosmolar serum and hyperosmolar urine
B. Hypoosmolar serum and hyperosmolar urine
C. Hypoosmolar serum and hypoosmolar urine
D. Hyperosmolar serum and hypoosmolar urine
Correct Answer: B. Hypoosmolar serum and hyperosmolar urine
Rationale: SIADH leads to water retention, resulting in hypoosmolar serum (diluted plasma) and failure to dilute urine appropriately, causing hyperosmolar urine.
A 40-year-old man is diagnosed with pituitary diabetes insipidus. Which of the following is the primary treatment to manage his condition?
A. Intravenous administration of hypertonic saline
B. Desmopressin (DDAVP) via IV, nasal spray, or oral administration
C. Fluid restriction to prevent excessive water loss
D. Administration of tolvaptan to reduce water excretion
Correct Answer: B. Desmopressin (DDAVP) via IV, nasal spray, or oral administration
Rationale: Desmopressin (DDAVP) is the treatment of choice for pituitary (central) DI. It selectively acts on V2 receptors to increase urine concentration and reduce urine output. It can be administered via IV, SC, nasal spray, or oral forms. Hypertonic saline and tolvaptan are not appropriate for central DI. Fluid restriction alone would not address the underlying AVP deficiency.
A patient diagnosed with pituitary diabetes insipidus (DI) is started on desmopressin (DDAVP). What is the mechanism of action of this medication?
A. Blocks V1 receptors to reduce thirst
B. Inhibits renal water excretion by blocking sodium channels
C. Activates V2 receptors to promote water reabsorption
D. Stimulates ADH secretion from the posterior pituitary
Correct Answer: C. Activates V2 receptors to promote water reabsorption
Rationale: Desmopressin (DDAVP) is a synthetic analogue of AVP that selectively activates V2 receptors in the kidneys. This action increases water reabsorption, reduces urine output, and concentrates the urine.
Which of the following is the most common type of diabetes insipidus (DI)?
A. Nephrogenic DI
B. Central DI
C. Primary polydipsia
D. Gestational DI
Correct Answer: B. Central DI
Rationale: The most common type of DI is central DI, caused by a primary deficiency in AVP secretion. It is also referred to as neurohypophyseal, neurogenic, pituitary, cranial, or central DI.
A patient presents with excessive thirst and large volumes of dilute urine. Following a water deprivation test, plasma osmolarity remains low, and the patient has a history of obsessive-compulsive disorder. What is the most likely subtype of their condition?
A. Dipsogenic DI
B. Psychogenic polydipsia
C. Iatrogenic polydipsia
D. Nephrogenic DI
Correct Answer: B. Psychogenic polydipsia
Rationale: Psychogenic polydipsia involves excessive water intake without a thirst mechanism and is commonly associated with psychiatric disorders such as obsessive-compulsive disorder or psychosis.
Gestational diabetes insipidus (DI) is primarily caused by:
A. Renal insensitivity to AVP
B. Increased degradation of AVP by placental enzymes
C. Excessive fluid intake during pregnancy
D. Autoimmune damage to the hypothalamus
Correct Answer: B. Increased degradation of AVP by placental enzymes
Rationale: Gestational DI is caused by an increased rate of AVP degradation by an N-terminal aminopeptidase produced by the placenta. This condition typically resolves after delivery.
Nephrogenic diabetes insipidus is characterized by:
A. Increased AVP secretion in response to hyperosmolarity
B. Renal insensitivity to the antidiuretic effects of AVP
C. Suppression of thirst due to central nervous system damage
D. Overproduction of AVP by the posterior pituitary
Correct Answer: B. Renal insensitivity to the antidiuretic effects of AVP
Rationale: Nephrogenic DI occurs when the kidneys fail to respond to AVP, resulting in an inability to concentrate urine. Causes include genetic mutations, lithium toxicity, and electrolyte imbalances such as hypokalemia.
Which of the following conditions is a potential cause of dipsogenic diabetes insipidus?
A. Head trauma
B. Lithium toxicity
C. Obsessive-compulsive disorder
D. Hypokalemia
Correct Answer: A. Head trauma
Rationale: Dipsogenic DI is caused by inappropriate thirst due to hypothalamic damage, which may result from head trauma or multifocal brain diseases such as neurosarcoid or multiple sclerosis.
