(Diuresis/Polyuria – tasteless increased urine)

Insufficient ADH

Aetiology

• Central (damage to hypothalamus/post pit → no ADH production/release)
  • CNS trauma (pit. surg, head injury)
  • inflammation
  • stroke
  • tumour
• nephrogenic: (Tubular Resistance to ADH)
  • Abnormal ADH receptors
  • Drugs: lithium
  • Hypercalcaemia, hypokalaemia
  • Kidney diseases (→ impaired urine concentration)
    • Obstructive nephropathy
    • Chronic pyelonephritis
    • Analgesic nephropathy
    • Multiple myeloma
• gestational: placenta releases vasopressinase to break down ADH. starts in week 8, peaks 3rd trimester. Gets worse until birth.
• psychogenic polydypsia: drink ++water → decreased ADH → polyuria

Pathophysiology

decreased ADH (central), or response to ADH (nephrogenic) → decreased water reabsorption → dilute urine → polyuria → polydipsia and electrolyte imbalances (particularly hypernatremia).

Clinical Features

• polyuria (3L+/day)
• polydypsia

if cant reach water (unconscious, thirst centre damage)→ bad time

• dehydration
• low blood pressure