Diabetes Insipidus

Study guide:

Definitions:  

  • Disorder of ineffective ADH resulting in excretion of large volumes of dilute urine.

Types:

•   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

Etiology:

Clinical Presentation:

•   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

Diagnosis:

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

       a. Procedure

             • 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)

       b. Response

             •   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

Management:

Central 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.

 

Nephrogenic DI:

•   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

Complications:

•   Dehydration

•   Electrolyte imbalance

References:

  •    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].

First author: Fajr Alqahtani  

Format editor: Noura Alsubaie                  

" Soon "
  • --------------------------------icon-12
  • mzl.lzsnbijy
  • SoundCloud Social Icon
  • Facebook Social Icon
  • Twitter Social Icon
  • YouTube Social  Icon