diabetes insipidus
etiology
copied shamelessly from deranged physiology:
| central DI | nephrogenic DI |
|---|---|
| failure of posterior pituitary to produce ADH e.g. - Intracranial hemorrhage. - TBI (traumatic brain injury). - Neurosurgical complication. - Herniation, brain death. - Any mass lesion (e.g., brain tumors, aneurysms). - Infections (meningitis, encephalitis). - Inflammation, e.g.: - Checkpoint inhibitor hypophysitis. - IgG4-related hypophysitis. - Idiopathic autoimmune hypophysitis. - Infiltrative diseases, e.g. Neurosarcoidosis, Langerhans cell histiocytosis. - GBS (Guillain-Barre syndrome). (36578134) - Gestational diabetes insipidus |
resistance to ADH → failure to concentrate the urine e.g. - Medications: - Amphotericin. - Cidofovir. - Cisplatin. - Demeclocycline. - Foscarnet. - Ifosfamide. - Lithium use (chronic) - ~25% of patients on chronic lithium therapy - Vaptans. - Hypercalcaemia. - Severe hypokalemia. - AKI (acute kidney injury) and/or chronic kidney disease often cause impaired urinary concentration, including: - Post-ATN polyuria. - Postobstructive polyuria. - Multiple myeloma, amyloidosis. - Sickle cell disease. - Sjogren syndrome. |
clinical presentation
- polyuria
- polydipsia, thirst++
- failure to thrive
investigations
Hypernatraemia
↑ serum Osm
↑ urine volume
↑ urinary sodium
↓ urinary osmolality
(extracellular and intracellular fluid volume ↓)
water deprivation test – measure serum/urine osmolality + monitor weight.
Dxc: urine:plasma osmolality ratio < 2. Stop if: 3% body weight/4kg, or serum osmolality >300 mOsm/kg. Give vasopressin if osmolality remains <600 mOsm/kg
management
Nephrogenic: DDAVP no effect
Central: DDAVP causes ↑ urine Osm
Otherwise it's fluid restriction
Traditional teaching = correct Na by 12 mEq/L per day
- main concern = cerebral oedema from rapid correction
- probably higher risk in younger patients who have less space in the skull
- Free water deficit
➥ Cranial: underlying cause, test ant pituitary function ⇒ vasopressin/DDAVP
➥ Nephrogenic: treat cause, Na restriction, bendroflumethiazide/indometacin ⚠ s/e GI, agranulocytosis, renal s/e