Diabetes Insipidus Flashcards
what is diabetes insipidus
inadequate secretion of or insensitivity to ADH (vasopressin). this leads to hypotonic polyuria
what is central DI
inadequate secretion by the posterior pituitary glands
what is nephrogenic DI
the kidneys collecting duct do not respond to ADH
Water channels fail to activate and the luminal membrane of the collecting duct remains impermeable to water
causes of central DI
Idiopathic
Tumours (e.g. pituitary tumour)
Infiltrative (e.g. sarcoidosis)
Infection (e.g. meningitis)
Vascular (e.g. aneurysms, Sheehan syndrome)
Trauma (e.g. head injury, neurosurgery)
causes of nephrogenic DI
lithium drugs,
Post-obstructive uropathy
Pyelonephritis
Pregnancy
Osmotic diuresis (e.g. diabetes mellitus)
epidemiology
around 24 yrs
presenting symptoms
polyuria, polydipsia, hypotonic urine in large amounts, nocturia,
presenting symptoms in children especially
bed wetting and sleep disturbances
signs on physical examination
Central DI has few signs if the patient drinks sufficiently to maintain adequate fluid levels
Urine output > 3 L/day
If fluid intake < fluid output, signs of dehydration will be present (e.g. tachycardia, reduced tissue turgor, postural hypotension, dry mucous membranes)
Signs related to the cause (e.g. visual defect due to pituitary tumour)
investigations for diagnosing Diabetes insipidus
decreased urine and increased serum osmolarity,
serum glucose and electrolytes,
water deprivation test
water deprivation test
restrict water for 8 hours, weigh the patient, give desmopressin (ddAVP) and if it is DI:
urine can’t be concentrated,
how to distinguish between cranial and nephrogenic DI with desmopressin test
cranial; urine osmolarity rises by >50%
nephrogenic; urine osmolarity rises by <45%
treatment of cranial DI
give desmopressin
treatment of nephrogenic DI
thiazide like diuretics or sodium
protein restriction
