Diabetes insipidus Flashcards
define diabetes insipidus
Disorder of salt and water balance due to insufficient vasopressin secretion or decreased response to vasopressin
describe the water reabsorption mechanism that is effected in diabetes insipidus
- High serum osmolarity detected by osmoreceptors.
- Increased production (hypothalamus) and secretion (posterior pituitary) of vasopressin.
- Vasopressin acts on V2 receptors of late DCT and Collecting Duct of kidneys
Via GPCR mechanism, it increases the number of AQP2 channels which allows for water reabsorption from the kidney tubule to blood. - Absorption of water decreases serum osmolarity.
what are the two pathological mechanisms of diabetes insipidus?
- cranial
- nephrogenic
describe the cranial pathological mechanism of diabetes insipidus
-Impaired production of vasopressin in the hypothalamus/secretion from the posterior pituitarygland.
-Less vasopressin acts on V2 receptors in DCT & collecting duct thus increased water excretion.
describe the nephrogenic mechanism of diabetes insipidus
– Intrinsic defect of the kidney, where there is impaired response of V2 receptors in the DCT and collecting duct.
-Increased water excretion.
what are the causes of cranial diabetes insipidus?
-likely an autoimmune cause.
Other causes:
-Tumour/other infiltrative diseases
-Familial or congenital
-Trauma to the hypothalamus/posterior pituitary
what are the causes of nephrogenic diabetes insipidus?
-commonly hereditary
-Lithium toxicity – enters cells via ENaC and -disrupts AQP2 signally pathway
-Kidney disorders
what are the signs of diabetes insipidus?
-High serum osmolarity
-Hypernatremia
-Low urine osmolarity
what are the key symptoms of diabetes insipidus?
-Polyuria
-Polydipsia
-Dehydration
-CNS symptoms – mental slowing, headache, irritability, visual disturbances
-Nocturia
what are the other- more general- symptoms of diabetes insipidus?
-Lethargy
-Fatigue
-Weakness
-Myalgia
what investigations take place to diagnose diabetes insipidus?
Urine dip– check osmolarity
Blood test – check serum osmolarity
Water deprivation & desmopressin test
describe the water deprivation and desmopressin test results for cranial diabetes insipidus
After water deprivation – low urine osmolarity
After desmopressin – high urine osmolarity
describe the water deprivation and desmopressin test results for nephrogenic diabetes insipidus
After water deprivation – low urine osmolarity
After desmopressin – still low
what is the treatment for cranial diabetes insipidus?
Desmopressin
what is the treatment for nephrogenic diabetes insipidus?
Thiazides
