Diabetes Insipidus

Question 1

What is diabetes insipidus characterized by?

Answer 1

Passage of large volumes (>3L/24hrs) of dilute urine (osmolality <300)

Question 2

What is the normal physiological role of ADH (vasopressin)?

Answer 2

ADH is released from the hypothalamus and stored in the posterior pituitary, responding to increased serum osmolality to reabsorb water in the kidneys

Question 3

What are the consequences of diabetes insipidus on urine production?

Answer 3

Inability of kidneys to reabsorb water, leading to polyuria and polydipsia

Question 4

What characterizes primary polydipsia?

Answer 4

Normally functioning ADH system but excessive fluid intake leads to excessive urine production

Question 5

How is primary polydipsia distinguished from diabetes insipidus?

Answer 5

Using a fluid deprivation test

Question 6

What is neurogenic (cranial) diabetes insipidus?

Answer 6

Decreased ADH levels due to various causes such as mutations, brain tumors, or trauma

Question 7

List some causes of neurogenic diabetes insipidus.

Answer 7

• Mutations in vasopressin gene
• Brain tumors
• Brain trauma/injury
• Idiopathic causes
• Brain infections
• Vascular issues (e.g., Sheehan’s syndrome)
• Sarcoidosis
• Hemochromatosis
• Wolfram syndrome

Question 8

What is nephrogenic diabetes insipidus?

Answer 8

Condition where collecting ducts of kidneys do not respond to ADH

Question 9

What are some causes of nephrogenic diabetes insipidus?

Answer 9

• Idiopathic
• Medications (e.g., lithium)
• Mutations in ADH receptor gene
• Hypercalcaemia
• Hypokalaemia
• Kidney disease (e.g., polycystic kidney)

Question 10

What is dipsogenic diabetes insipidus?

Answer 10

Results from hypothalamic disease or trauma that damages the thirst mechanism

Question 11

What is gestational diabetes insipidus caused by?

Answer 11

Overproduction of vasopressinase by the placenta, which breaks down vasopressin (ADH)

Question 12

What are the clinical symptoms of diabetes insipidus?

Answer 12

• Excessive urination (>3L/24hrs)
• Excessive thirst (especially for ice-cold water)
• Nocturia
• Dehydration symptoms (headache, dizziness, dry mouth)

Question 13

What are some signs of diabetes insipidus?

Answer 13

• Hypotension
• Dilute urine
• Signs of dehydration (dry mucous membranes, prolonged capillary refill)

Question 14

What investigations are used to diagnose diabetes insipidus?

Answer 14

• 24-hour urine collection
• Plasma glucose
• U&Es (renal function, rule out electrolyte imbalance)
• Urine specific gravity
• Simultaneous plasma and urine osmolality
• Fluid deprivation test (desmopressin stimulation test)

Question 15

What urine osmolality results indicate primary polydipsia after water deprivation?

Answer 15

High (>800)

Question 16

What urine osmolality results indicate neurogenic and nephrogenic diabetes insipidus after water deprivation?

Answer 16

Low (<300)

Question 17

What is the management for neurogenic diabetes insipidus?

Answer 17

Desmopressin (to replace absent ADH) with monitoring of Na levels due to risk of hyponatraemia

Question 18

What is the management for nephrogenic diabetes insipidus?

Answer 18

• Drink enough water to satisfy thirst
• High-dose desmopressin
• Thiazide diuretics
• NSAIDs (reduce PGE2, reducing urine volume produced)

Question 19

What urine osmolality results indicate neurogenic diabetes insipidus after desmopressin?

Answer 19

high (>800)

Question 20

What urine osmolality results indicate nephrogenic diabetes insipidus after desmopressin?

Answer 20

low (< 300)