Disorder of ineffective ADH resulting in excretion of large volumes of dilute urine.
• Central DI— due to low ADH secretion by posterior pituitary (the most common form)
• Nephrogenic DI— ADH secretion is normal but tubules cannot respond to ADH i.e tubules do not reabsorb water
• Polyuria is a hallmark finding: 5 to 15 L daily; urine is colorless
• Thirst and polydipsia—as a compensatory mechanism
• Hypernatremia is usually mild unless the patient has an impaired thirst drive
1. Urine—low specific gravity and low osmolality indicate DI
2. Plasma osmolality
a. Normal: 250 to 290 mOsm/kg
b. Primary polydipsia: 255 to 280 mOsm/kg
c. DI: 280 to 310 mOsm/kg
3. A water deprivation test (dehydration test) is required to make the diagnosis
• Withhold fluids, and measure urine osmolality every hour (differentiate true DI from psychogenic DI)
• When urine osmolality is stable (<30 mOsm/kg hourly increase for 3 hours), inject 2 g desmopressin subcutaneously. Measure urine osmolality 1 hour later (distinguish central from nephrogenic DI)
• increase in urine osmolality (>280 mOsm/kg) with dehydration: normal or psychogenic DI
• no responce to dehydration but respnd to ADH: Central DI
• no responce to dehydration + ADH: Nephrogenic DI
4. ADH level (not the test of choice; takes a long time to get results)
a. Low in central DI
b. Normal or elevated in nephrogenic DI
• Desmopressin (DDAVP) is the primary therapy and can be given intranasally as a spray 10–40 μg once or twice daily, but can also be given orally as 100–200 μg 3 times daily, or intramuscularly 2–4 μg daily.
• Chlorpropamide increases ADH secretion and enhances the effect of ADH.
• Treat the underlying cause.
• treat with sodium restriction and thiazide diuretics
- These deplete the body of sodium, which leads to increased reabsorption of sodium and water in the proximal tubules
- The reabsorption of sodium and water in the proximal tubules means that less water reaches the distal tubules, leading to decreased urine volume
• Electrolyte imbalance
Kumar, P. and Clark, M. (n.d.). Kumar & Clark's clinical medicine. 8th ed. Spain: Elsevier Ltd., pp.992-993.
Kim, J. and Mukovozov, I. (n.d.). Toronto Notes 2017. 33rd ed. Toronto, Ontario, Canada: Toronto Notes for Medical Students, Inc., p.E18.
Agabegi, S. and Agabegi, E. (n.d.). Step-up to medicine. 4th ed. Lippincott Williams & Wilkins, a Wolters Kluwer business, pp.178-179.
nhs.uk. (2018). Complications. [online] Available at: https://www.nhs.uk/conditions/diabetes-insipidus/complications/ [Accessed 23 Sep. 2018].