PBL: Nephrogenic Diabetes Insipidus

  • By: Terri
  • Date: April 22, 2010
  • Time to read: 2 min.


  • 28 y/o female marketing executive
  • thirsty often
  • urinate frequently
  • ongoing: 3 months
  • drinks 8-16 glasses of water & several cans of juice in 2-3 hours
  • consumes caffeine-free drinks & non-alcoholic drinks only
  • tried limiting fluid intake – no improvement
  • otherwise healthy, no past medical history
  • Sodium high
  • Osmolality high
  • Water deprivation test – urine osmolality remain high after given DDAVP


  • Diabetes
  • Pituitary Tumour
  • Vasopressin resistance in distal nephron
  • Stress/Anxietry

Final hypothesis:

Nephrogenic diabetes insipidus

Extra learning issues:

  • Dipsogenic Diabetes Insipidus
    -Defect to the thirst mechanism located in the anterior hypothalamus, results in an abnormal increase in thirst & fluid intake that suppresses ADH & increase urine output. Desmopressin/DDAVP is ineffective — will lead to fluid overload if thirst remains.
  • Gestational Diabetes Insipidus
    -Occurs during pregnancy, woman produce vasopressinase in the placenta which breakdowns vasopressin. Can be treated with DDAVP. Some diseases of pregnancy activates hepatic vasopressinase (pre-ecclapsia, acute fatty liver etc.)


What is meant by thirsty?

  • Sensation of dryness of throat and mouth that drives the desire to drink

Why does she feel thirsty?

  • Thirst centre in the hypothalamus is stimulated. The thirst mechanism regulates the water level, decrease in plasma volume of 10% of more and/or increase in plasma osmolality by 1-2%, will cause dryness of mouth (less saliva produced) and stimulation of the hypothalamic thirst centre. Thirst is quickly gone after water is taken in, although the water has yet to be absorbed by the blood. Feedback signals are sent to the thirst centre, inhibiting it.

What is the normal frequency of urination?

  • Depends on the fluid intake
  • Micturition is the act of emptying the bladder
  • When 200ml of urine has accumulated, the bladder wall distends, causing activation of stretch receptors –> triggering a visceral arc.

How to calculate the body mass index?

  • BMI= weight (kg) / Height2 (m)
  • <18.5 : Underweight
    18.5-24.9: Normal
    25-29.9: Overweight
    30: Obese

What signs would you look for in a person who is having polydipsia & polyuria? Signs of dehydration.

  • Dry mouth
  • Loss of skin turgor
  • Sunken eyes
  • Reduced BP varying with posture (Systolic <90. Diastolic <60)
  • Increase pulse rate (>90/minute)

What is blood pressure?

  • force per unit area
  • exerted on the wall of a blood vessel by its contained blood

What is pulse rate?

  • Pulse: Rhythmical dilation of an artery, produced by the increased volume of blood into the vessel by the contraction of the heart.
  • Pulse rate: Frequency of the arterial pulsation palpated per minute

What is the composition of intracelluar & extracelluar fluids of the body?

  • Find out

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