Diabetes insipidus (Posterior Pituitary) Flashcards
Where are posterior pituitary hormones synthesized?
In specialized neurons in the hypothalamus.
What are the two hormones of the posterior pituitary?
Vasopressin and oxytocin.
What is diabetes insipidus?
A condition causing the excretion of large volumes of hypotonic urine leading to polyuria and polydipsia.
What urine volume is typical in diabetes insipidus?
More than 50-60 mL/kg/day.
What are the four main causes of diabetes insipidus?
Central diabetes insipidus nephrogenic diabetes insipidus gestational diabetes insipidus and primary polydipsia.
What causes central diabetes insipidus?
The inability to secrete or synthesize vasopressin in response to increased osmolality.
What causes nephrogenic diabetes insipidus?
The kidney’s inability to respond to vasopressin.
What causes gestational diabetes insipidus?
Elevated placental cystine aminopeptidase (vasopressinase) during pregnancy.
What causes primary polydipsia?
A disorder of thirst stimulation leading to excessive water intake.
What are common causes of pituitary diabetes insipidus?
Head trauma neoplasms (craniopharyngioma metastatic lung or breast cancer) granulomas (neurosarcoidosis) and vascular issues like Sheehan’s syndrome.
What are common causes of nephrogenic diabetes insipidus?
Drugs like lithium and aminoglycosides metabolic conditions like hypercalcemia and hypercalciuria vascular conditions like sickle cell disease and ischemia and infiltrative diseases like amyloidosis.
What are common causes of primary polydipsia?
Psychogenic conditions like OCD head trauma and multiple sclerosis.
What are the main symptoms of diabetes insipidus?
Polyuria urinary frequency enuresis nocturia polydipsia and mild daytime fatigue.
What urine findings suggest diabetes insipidus?
24-hour urine volume >50 mL/kg with an osmolality <300 mosmol/L.
When should diabetes insipidus be suspected?
In patients with significant polyuria >50 mL/kg/day.
How can diabetes insipidus be diagnosed?
By detecting inappropriately low urine osmolality despite high plasma osmolality due to increased serum sodium.
How is central diabetes insipidus distinguished from nephrogenic diabetes insipidus?
By administering vasopressin and observing urine response.
What response to desmopressin confirms central diabetes insipidus?
A marked increase in urine osmolality >50%.
What response to desmopressin confirms nephrogenic diabetes insipidus?
Little to no increase in urine osmolality.
What test helps differentiate nephrogenic from central diabetes insipidus?
Plasma vasopressin levels which are elevated in nephrogenic diabetes insipidus especially after dehydration.
What imaging study is used to evaluate the cause of diabetes insipidus?
MRI of the hypothalamic-pituitary region.
What is the primary treatment goal for diabetes insipidus?
To reduce polyuria and polydipsia while avoiding water retention and hyponatremia.
What is the preferred treatment for hypothalamic diabetes insipidus?
The vasopressin agonist desmopressin.
What forms of desmopressin are available?
Oral tablets (0.1 mg or 0.2 mg) and intranasal sprays (10-20 μg).
What oral medication can enhance vasopressin effects in partial central diabetes insipidus?
Chlorpropamide (100-500 mg daily).
