Pathology: Deficiency of anti-diuretichormone causing free water loss.
Can be central (failure of posterior pituitary toproduce ADH) or nephrogenic (failure of kidneys to respond to ADH)
Aetiology: Central: Tumour, infiltration, infection, trauma or congenital.
Nephrogenic: Drugs(e.g. Lithium, Demeclocycline, Colchicine), familial (X-
linked AVP receptor gene), CKD
Symptoms: Polydipsia,polyuria, weight loss
Signs: Dehydration, dehydration
Investigations: Bloods: U&E (hypernatraemia) andplasma osmolarity (raised)
MSU: Urine osmolarity(low)
Imaging: MRI pituitary
Water Deprivation Test: Waterrestricted for 8 hours then desmopressin given
If urine concentrated after desmopressin – Cranial DI
If urine dilate after desmopressin – Nephrogenic DI
Treatment: Central: Find underlying cause and Desmopressin.
Nephrogenic: Stop offendingmedications
Complications: Neurological sequelae if hypernatraemiacorrected rapidly)
Prognosis: Lifeexpectancy not affected if treated.
Figure 5.8 Water Deprivation Test
