diabetes insipidus Flashcards
Pathoetiology of DI ?
decreased secretion of antidiuretic hormone (ADH) from the pituitary (cranial DI) or an insensitivity to antidiuretic hormone (nephrogenic DI)
what is DIDMOAD
association of cranial Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness (also known as Wolfram’s syndrome)
causes of cranial DI ?
idiopathic
pituitary surgery
craniopharyngioma
infiltrative
histiocytosis
sarcoidosis
haemochromatosis
DIDMOAD
causes of nephrogenic DI
MOST COMMON GENETIC :
affects the vasopression (ADH) receptor
LITHIUM - desensitizes the kidney’s ability to respond to ADH in the collecting ducts
electrolytes
-HYPERCALCEMIA - hyperparathyroidism
-HYPOKALAEMIA
tubulo-interstitial disease: obstruction, sickle-cell, pyelonephritis
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clinical presentation of DI ?
history of polyuria, thirst and nocturia.
dry mucous membranes, tachycardia and mild orthostatic hypotension
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diagnosis of DI
high plasma osmolality,
low urine osmolality
urine osmolality of >700 mOsm/kg excludes diabetes insipidus
water deprivation test
desmopressin test - if cranial or nephrogenic urine osmolality increases (amount of water in urine increases)
what is seen in desmopressin test ?
cranial DI - with desmopressin the urine osmolality should increase
nephrogenic desmopressin - urine osmolality is unchanged
Water deprivation test indicated for ?
used to determine whether the patient has diabetes insipidus as opposed to other causes of polydipsia (a condition of excessive thirst that causes an excessive intake of water)
Psychogenic polydipsia - urine osmolality increases
DI - urine osmolality remains low
what is low irine osmolality seen in DI
<300
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management of DI ?
nephrogenic DI - thiazides , Low salt and protein diet
cranial DI - desmopressin
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what is psychogenic polydipsia
Initial plasma osmolality is high in DI.
a patient drinking excessive quantities of water leading to increased polyuria. In these patients, the primary finding is an initially low plasma osmolality. Following water deprivation, the patient’s urine becomes appropriately concentrated.
Water deprivation test: primary polydipsia
urine osmolality after fluid deprivation: high
urine osmolality after desmopressin: high
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Syndrome of inappropriate ADH (SIADH) secretion results in excess ADH, what is the plasma and urine osmolality result for this patient
This results in low plasma osmolality and a high urine osmolality initially,
