Diabetes Insipidus

Question 1

Definition of diabetes insipidus

Answer 1

3+ L daily urine, decreased ADH secretion/action

Question 2

What are the 2 types?

Answer 2

Cranial
Nephrogenic

Question 3

What is cranial diab insip?
Causes of it?

Answer 3

Decreased ADH secretion
Causes: ADH gene mutation, pituitary adenoma, idiopathic

Question 4

What is nephrogenic diab insip?
Causes of it?

Answer 4

Decreased kidney response to ADH
Renal tubular acidosis, ADH-R mutation, Metabolic (low K+, high Ca2+), drugs (lithium), chronic renal disease

Question 5

Pathology

Answer 5

Low ADH = high H2O lost in urine; dilute high volumes of urine
Less water reabsorbed

Question 6

Symptoms

Answer 6

Polyuria
Polydipsia
Hypernatremia
Lethargy
Confusion
Coma
Severe dehydration

Question 7

How to diagnose diabetes insipidus?

Answer 7

3+ L dilute urine daily (24hr) = suspect

1. Gold standard: water deprivation test (no fluid for 8 hours)
   Normally = serum osm stays normal, urine osm increases
   DI = serum osm rises while urine osm unchanged
2. Inject IM desmopressin (differentiate cranial and nephrogenic)
   Cranial : before <300 LOW, after >800 HIGH = adequate ADH to have effect on kidney

Nephrogenic : before <300 LOW, after <300 LOW = ADH will have no affect on kidney

Question 8

Treatment for diabetes insipidus
cranial and nephrogenic

Answer 8

Cranial = desmopressin (synthetic ADH)
Nephrogenic = thiazides (bendroflumethiazide) + treat underlying cause