Endocrinology

Question 1

Diabetes Insipidus vs Psychogenic Polydipsia

(Types of DI and their pathophys, Causes of each type, Management of each type, How to differentiate different types of DI and PP)

Answer 1

Both presents with polydipsia and polyuria

Cranial Diabetes Insipidus
- Inability to produce ADH
- Causes
- Idiopathic
- Trauma
- Pituitary surgery
- Craniopharyngiomas
- Management
- Desmopressin

Nephrogenic Diabetes Insidipus
- Renal tubules not responsive to ADH. Cortical & Medullary collecting tubules affected
- Causes
- Drugs (Lithium and Doxycycline)
- Genetic (X-Linked Vasopressin 2 Receptor Mutation or Aquaporin 2 gene mutation)
- CKD
- Management
- Congenital: Sildenafil (reduce urine output)
- Lithium induced: Stop lithium. If fail, can trial thiazides (ie. amiloride)

Water Deprivation Test (Desmopressin Test)
- Deprive water for 8 hours, check urine osmol, give desmopressin (synthetic ADH), recheck urine osmol after another 8 hours
(Urine osmol levels) After Deprivation After Desmopressin
Cranial DI Low High (finally has ADH to reabsorb water)
Nephrogenic DI Low Low (Still not responsive)

Psychogenic Polydipsia High (Removed the source of excess H2O)