Polyuria
Definition: >2L/m2/day
Causes:
- Glucose-induced osmotic diuresis in uncontrolled diabetes mellitus
- Primary polydipsia (aka psychogenic)
- drugs affecting thirst / hyponatremia
- Diabetes insipitus
- Central (reduced ADH secretion)
- autoimmune, trauma, pituitary surgery, or hypoxic or ischemic encephalopathy
- Nephrogenic
- Genetic e.g. ADH insensitivity
- X-linked hereditary nephrogenic DI (mutations in the AVPR2 gene encoding the ADH receptor V2)
- AR/AD nephrogenic DI due to mutations in the aquaporin-2 gene
- Sickle cell
- Cystic kidney disease
- ADPKD
- MCKD
- Bardet-Biedl syndrome
- Bartter syndrome (Na, K wasting)
- Lithium
- Hypercalcaemia
- Genetic e.g. ADH insensitivity
- Central (reduced ADH secretion)
BSL > if pos > DM
Water deprivation
ADH administration (desmopressin)
Primary polydipsia: urine osmo >500 with deprivation, no response to ADH
Central DI: minimal response to deprivation, osmo >300 post ADH (100% increase in complete, 15-50% in partial central)
Nephrogenic DI: no response to deprivation, osmo still <300 post ADH (0% increase in complete, <50% in partial nephrogenic)
Rx
Nephrogenic
- in young > offer water every 2 hours
- some require continuous gastric feeding
- low Na, low protein diet (reduce solute load)
- NSAID (inhibits renal prostaglandins, which inhibit ADH)
- Diuretic (enhances renin-angiotensin to maximise Na/H20 resorption in PT rather than relying on ADH)
- If partial, Desmopressin (supraphysiological levels can partially overcome insensitivity)
- Monitor growth
- once thirst developed usually can self regulate
complications
Intellectual impairment from recurrent hypernatraemic dehydration