Diabetes insipidus: central/nephrogenic

Question 1

Define diabetes insipidus

Answer 1

Central diabetes insipidus: when too little ADH is produced

Nephrogenic diabetes insipidus: when the collecting ducts don’t respond to ADH

Question 2

What are the causes and risk factors for developing diabetes insipidus

Answer 2

Nephrogenic causes:

1. ) Drugs: e.g. lithium which is used to treat bipolar disorder
2. ) Genetic: mutation on the AVPR22 gene on the X chromosome
3. ) Intrinsic kidney disease

Central causes:

1. ) Brain surgery
2. ) Brain damage

Question 3

What are the causes and risk factors for developing diabetes insipidus

Answer 3

Nephrogenic causes:

1. ) Drugs: e.g. lithium chloride which is used to treat bipolar disorder
2. ) Genetic: mutation on the AVPR2 gene on the X chromosome
3. ) Renal tubular acidosis
4. ) Hypokalaemia
5. ) Hypercalcaemia
6. ) Sickle cell disease

Central causes:

1. ) Neurosurgery
2. ) Head trauma
3. ) Pituitary tumour
4. ) Infiltrative disease: sarcoidosis/histiocytosis
5. ) Congenital defect

NOTE – damage to the Hypothalamo-neurohyophysial tract or posterior pituitary with an intact hypothalamus does NOT cause ADH deficiency as ADH can still “leak” from the damaged end of the intact neurone

Question 4

Describe the signs of diabetes insipidus

Answer 4

• Polydipsia

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Question 5

Describe the signs of diabetes insipidus

Answer 5

• Polyuria/Nocturia
• Polydipsia
• Dehydration

Question 6

Describe the symptoms of diabetes insipidus

Answer 6

• Polyuria/Nocturia
• Polydipsia
• Dehydration

Question 7

What are the investigations and diagnosis for diabetes insipidus

Answer 7

1. ) Desmopressin stimulation test (water deprivation test):
   - Patient fasts for 8 hours: no food or water and at the end of the 8 hours will have a urine osmolality test.
   - Then they are given desmopressin (synthetic ADH) and their urine osmolality is tested at the end of an 8 hour period.
   - Results:
2. ) Nephrogenic: Low U.O and low U.O after ADH.
3. ) Central: Low U.O and high U.O after ADH.
4. ) Primary polydipsia: high U.O at start of test
5. ) U&E’s: shows hypernatremia, high serum osmolality and low urine osmolality
6. ) Urine test: confirm polyuria
7. ) Plasma biochemistry: high Na+
8. ) MRI of hypothalamus

Question 8

Describe the treatment and management of diabetes insipidus

Answer 8

• Central DI: desmopressin given
• Nephrogenic DI:
  1. ) Bendroflumethiazide (diuretic): causes increased sodium secretion in DCT, increased water lost makes body respond by reducing GFR. Basically makes urine more concentrated
  2. ) NSAIDs: reduce GFR by inhibiting prostaglandin synthase (prostaglandins locally inhibit ADH action)