Diabetes insipidus is an endocrine disease marked by:
Pathophysiology of diabetes insipidus
1) clinical state of diabetes insipidus is marked by excessive production of dilute urine
2) caused by decreased secretion or activity of arginine vasopression
3) occurs in primary, secondary (or primary polydipsia), nephrogenic, gestational, and congenital forms
4) primary form – marked by decreased secretion of vasopressin and marked by destruction of neurohypophysis (trauma, infection, inflammation, neoplasm)
5) secondary form – decreased secretion of vasopressin and occurs in setting of known disease
6) nephrogenic form – marked by normal secretion but decreased activity of vasopressin
7) gestational from – usually resolves after delivery
Signs and Symptoms
1) polydipsia
2) polyuria
3) nocturia
4) urine output > 50 mL/kg a day
Characteristic Test Findings
1) urine osmolality < 300 mmol/kg
2) if water intake is restricted hypernatremia occurs
Associated Conditions
Primary Form
1) head trauma
2) brain tumors
3) neurosarcoid
4) toxoplasmosis
5) meningitis
6) Wegener’s granulomatoses
7) lupus
8) scleroderma
Secondary Form
9) schizophrenia
10) obsessive-compulsive disease
11) abnormally increased thirst states (tuberculosis, mulitple sclerosis, lithium use, carbamazepine)
Nephrogenic Form
12) amphotericin B use
13) lithium
14) aminoglycoside use
15) hypercalcemia
16) sarcoma
17) amyloidosis
18) obstruction of ureter or urethra
Biochemistry
secondary form (or primary polydipsia form) – inhibition of vasopressin secretion by excessive fluid intake
Treatment
Primary form
1) DDAVP (increases urine concentration and decreases urine flow) twice a day for several weeks
2) chlorpromide (Diabinese)
Secondary form
3) DDAVP in a small bedtime dose long-term
Nephrogenic form
4) thiazide diuretic/amiloride
5) low-sodium diet
6) some clinicians also use indomethacin
Tips for USMLE
1) can be present with normal serum soidum and no dehydration if patient has unrestricted access water intake or there is a defect in thirst
2) DDAVP is effective only for primary and secondary forms and not nephrogenic form
3) primary and secondary forms sometimes referred to as central DI
4) if a 42 year old woman suffers a severe head injury as an unrestrained passenger in a motor vehicle accident and is in the neurointensive care unit on day 3 when the nurse informs you that the patient has put out 4 L of clear urine in the past 12 h and has a sodium of 153 mEq/L think diabetes insipidus
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