- Is the passage of large volumes of inappropriately diluted urine in the presence of concentrated plasma – due to reduced secretion or reduced efficacy of ADH (released from posterior pituitary)
- It is uncommon, is linke to polyuria (>2.5L/d) and polydipsia and must NOT be due to..
- DM or renal failure
- Primary psychogenic polydipsia
- Types of DI:
- o Cranial DI: relative or absolute ADH deficiency. Causes: familial, idiopathic, trauma to hypothalamo-pituitary region, surgical, infiltration of posterior pituitary/hypothalamus (secondary deposits/sarcoid), infections (TB, meningitis)
- o Nephrogenic DI: renal resistance to ADH. Causes: lithium toxicity, familial, post-obstructive uropathy, hypokalaemia/hypercalcaemia, SCA, amyloid.
- Tx: unrestricted access to fluids and desmopressin (long-acting analogue of ADH).