Diabetes Insipidus

Presentation

Polydipsia
Polyuria

Causes

Cranial DI

idiopathic
post head injury
pituitary surgery
craniopharyngiomas
histiocytosis X
DIDMOAD is the association of cranial Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness (also known as Wolfram's syndrome)

Nephrogenic DI

genetic: the more common form affects the vasopression (ADH) receptor, the less common form results from a mutation in the gene that encodes the aquaporin 2 channel
electrolytes: hypercalcaemia, hypokalaemia
drugs: demeclocycline, lithium
tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis

Laboratory investigations

High plasma osmolarity

Water deprivation test

Urine osmolarity is low with DI, typically <300 mOsmol/L.

Admisinistation of DDAVP will rectify cranial DI, with the osmolarity rising to >600 mOsmol/L
Nephrogenic DI does not respond to DDAVP

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