22. Diabetes insipidus

Question 1

etiology of diabetes insipidous ?

Answer 1

Central diabetes insipidus (CDI); most common form: caused by insufficient or absent hypothalamic synthesis or secretion of antidiuretic hormone (ADH) from the posterior pituitary

Primary (∼ ⅓ of cases)
Most cases are idiopathic.

Secondary (∼ ⅔ of cases)
Brain tumors (especially craniopharyngioma) and cerebral metastasis (most common: lung cancer and leukemia/lymphoma)

Neurosurgery: usually after the removal of large adenomas
Traumatic brain injury,
pituitary bleeding, subarachnoid hemorrhage
Pituitary ischemia (e.g., Sheehan syndrome, ischemic stroke)
Infection (e.g., meningitis)

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Nephrogenic diabetes insipidus (NDI);
caused by defective ADH receptors in the distal tubules and collecting ducts

Hereditary (mutation in ADH receptor; very rare)

Acquired
multiple myeloma

Adverse effect of medications (lithium, demeclocycline)

Renal disease (e.g., autosomal dominant polycystic kidney disease, renal amyloidosis)

Pregnancy - increased metabolism of vasopressin in pregnancy due to the placenta making an enzyme

Question 2

clinical features of diabetes insidious ?

Answer 2

Polyuria with dilute urine

Nocturia → restless sleep, daytime sleepiness
abscise of this the diagnosis of DI unlikely

Polydipsia (excessive thirst)

In cases of low water intake → severe dehydration (altered mental status, lethargy, seizures, coma) and hypotension

Question 3

what is the diagnosis of DI ?

Answer 3

central and nephrogenic DI
mild hypernatremia
ADH decreased in central
ADH - normal or increased in nephrogenic

plasma osmolality - high
urine osmolality - low
urine specific gravity less than 1.005

After obtaining baseline lab values, patients stop drinking water for 2–3 hours before the first measurement

After 2–3 hours without drinking water
Test urine volume and osmolality every hour

Test sodium and plasma osmolality every two hours

Water deprivation continues until one of the following occurs:
Urine osmolality rises and reaches a normal value→ DI ruled out and primary polydipsia confirmed

No change in urine osmolality despite a rising plasma osmolality

administer desmopressin (a synthetic ADH analog)

Monitor urine osmolality testing every 30 minutes for 2 hours
In CDI: Urine osmolality rises after desmopressin administration (renal ADH receptors are intact).
In NDI: Urine osmolality remains low after desmopressin administration (defective renal ADH

Question 4

what is the treatmnet for DI ?

Answer 4

Central diabetes insipidus
Desmopressin: synthetic vasopressin without vasoconstrictive effects

Administration: intranasal, subcutaneous, or oral

Important side effect: hyponatremia

or chloropropamide

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nephrogenic

A low-salt, low-protein diet reduces urine outpu

thiazide diuretics lead to sodium depletion, which causes sodium and water reabsorption in the proximal tubules. As a result, less water reaches the ADH-sensitive distal collecting tubules

NSAIDs - indomethacin

Amiloride : Indicated in patients with lithium-induced NDI; amiloride blocks lithium entry through the sodium channel.