Diabetes insipidus

Question 1

What are the two types of diabetes insipidus?

Answer 1

Cranial Diabetes Insipidus: Lack of antidiuretic hormone (ADH) production in the hypothalamus.
Nephrogenic Diabetes Insipidus: Kidneys do not respond to ADH.

Question 2

What is the role of antidiuretic hormone (ADH)?

Answer 2

ADH, also known as vasopressin, is produced in the hypothalamus and secreted by the posterior pituitary. It stimulates water reabsorption in the kidneys’ collecting ducts.

Question 3

What are the main symptoms of diabetes insipidus?

Answer 3

• Polyuria (excessive urination)
• Polydipsia (excessive thirst)

Question 4

What distinguishes primary polydipsia from diabetes insipidus?

Answer 4

In primary polydipsia, the ADH system is functioning normally, but excessive water intake causes polyuria. It is not diabetes insipidus.

Question 5

What are the causes of nephrogenic diabetes insipidus?

Answer 5

• Medications (e.g., lithium)
• Genetic mutations in ADH receptor gene (X-linked)
• Hypercalcaemia (high calcium)
• Hypokalaemia (low potassium)
• Kidney diseases (e.g., polycystic kidney disease)

Question 6

What are the causes of cranial diabetes insipidus?

Answer 6

• Brain tumors
• Brain injury
• Brain surgery
• Brain infections (e.g., meningitis, encephalitis)
• Genetic mutations in ADH gene (autosomal dominant)
• Wolfram syndrome (also causes optic atrophy, deafness, and diabetes mellitus)

Question 7

What are the common presenting features of diabetes insipidus?

Answer 7

• Polyuria (more than 3 liters of urine per day)
• Polydipsia (excessive thirst)
• Dehydration
• Postural hypotension

Question 8

What are the key investigation findings for diabetes insipidus?

Answer 8

• Low urine osmolality (dilute urine)
• High or normal serum osmolality
• More than 3 liters of urine in a 24-hour collection

Question 9

What is the water deprivation test used for in diabetes insipidus diagnosis?

Answer 9

The water deprivation test (desmopressin stimulation test) helps differentiate between primary polydipsia and diabetes insipidus by assessing urine osmolality before and after desmopressin administration.

Question 10

What are the urine osmolality results for primary polydipsia in the water deprivation test?

Answer 10

In primary polydipsia, urine osmolality will be high after water deprivation (desmopressin not required).

Question 11

What are the urine osmolality results for cranial diabetes insipidus in the water deprivation test?

Answer 11

In cranial diabetes insipidus, urine osmolality will be low after water deprivation and will increase after desmopressin is given.

Question 12

What are the urine osmolality results for nephrogenic diabetes insipidus in the water deprivation test?

Answer 12

In nephrogenic diabetes insipidus, urine osmolality will remain low both before and after desmopressin is given.

Question 13

How is cranial diabetes insipidus managed?

Answer 13

Cranial diabetes insipidus is treated with desmopressin (synthetic ADH) to replace the absent hormone. Serum sodium should be monitored to avoid hyponatraemia.

Question 14

How is nephrogenic diabetes insipidus managed?

Answer 14

• Ensuring access to plenty of water
• High-dose desmopressin
• Thiazide diuretics
• NSAIDs

Question 15

What is a potential complication when treating cranial diabetes insipidus with desmopressin?

Answer 15

There is a risk of hyponatraemia (low sodium) when using desmopressin, so serum sodium levels must be monitored.