Diabetes insipidus Flashcards
What are the main types of DI?
Central DI (CDI) – deficiency in the secretion of antidiuretic hormone (ADH). Complete or partial
Nephrogenic DI (NDI) – renal insensitivity to ADH. Congenital or acquired
Gestational (decrease in vasopressin d/t increase in metabolism of placental vasopressinase)
Primary PD - secondary to psycogenic PD or dypsogenic PD
What is the typical signalment of DI?
Any, but typically young
What can lead to inadequate ADH (central DI)?
Trauma Idiopathic Congenital defect Neoplasia Parasites
What can cause nephrogenic DI?
Congenital.
Secondary to drugs (e.g., lithium, demeclocycline, and methoxyflurane).
Secondary to endocrine and metabolic disorders (e.g., hyperadrenocorticism, hypokalemia, pyometra, and hypercalcemia).
Secondary to renal disease or infection (e.g., pyelonephritis, chronic renal failure, pyometra, ureteral obstruction).
Paraneoplastic syndrome (leiomyosarcoma)
What are the main Ddx for DI?
Hyperadrenocorticism. Diabetes mellitus. Liver disease – portosystemic shunt. Hyperadrenocorticism. Pyometra. Pyelonephritis. Hyperthyroidism – cats. Hypercalcemia. Psychogenic polydipsia. Renal failure Hyperaldosteronism Polycythaemia Neoplasia
What would you find on routine testing with DI?
Biochem usually normal but can see high Na
Urinary specific gravity low (usually <1.012, often <1.008).
Imaging MRI or CT scan if a pituitary tumor is suspected.
How can you try testing for DI after everything else is ruled out?
Water deprivation test
Trial Tx with ADH
Outline the water deprivation test
The animal is confined to a cage with no food or water and is weighed at 1- to 2-hour intervals after emptying the urinary bladder and getting an initial body weight. When >5% of body weight has been lost, the urinary bladder should be completely emptied and the urine checked for specific gravity or osmolality. A urine specific gravity >1.025 or urine osmolality >900 mOsm/l is generally considered an adequate response to water deprivation. Failure to concentrate urine to this degree in the absence of renal disease indicates either central or nephrogenic DI, and/or medullary washout. Immediately following water deprivation, if the animal fails to concentrate urine adequately after losing 5% or more of its body weight, an ADH response test is performed. A synthetic form of ADH (desmopressin acetate [DDAVP®]) may be given subcutaneously or intravenously, or 20 µg of DDAVP (about 4 drops of the 100 µg/ml intranasal preparation) can be administered as intranasal or conjunctival drops. Urine-concentrating ability is then monitored every 2 hours for 6 to 10 hours. Increases in urine specific gravity >1.025 or urine osmolality >900 mOsm/l after administration of aqueous vasopressin or DDAVP is suggestive of central DI. An inability to concentrate urine after ADH administration indicates nephrogenic DI or severe medullary washout.
What is the Tx for DI?
Central - DDAVP
Nephrogenic - hydrochlorothiazide and low Na diet
Outline vasopressin in the body
Made by hypothalamus
Released with oxytocin by posterior lobe/ neurohypophysis.
Stored in excretory granules. Released by exocytosis in response to stimuli
What are the AVP receptors in the body?
V1a V1b V2 oxytocin
How does AVP work/
Role = regulate body fluid homeostasis
Promotes re absorption of solute free H20 in distal tubules and collecting duct
Adds aquaporins to cell membrane
What happens in central DI?
Complete - no releasable AVP
Partial - subnormal AVP quantities. Osmoreceptors have higher thresholds to start releasing AVP
Outline the picture of nephrogenic DI
Kidney unable to concentrate u+
AVP normal
PUPD, high Na, high temp, dehydration, possible mental retardation
Genetic, mostly X linked
What can cause primary PD
Animals left alone in house/ changes in lifestyle or environment
Often change in environment can help
