CC Jan 2016 Diabetes inspidus

echoecho's version from 2016-03-06 16:47


Question Answer
Define?A rare disorder characterized by excessive thirst, profound polyuria (> 20 liters/day in some cases) and low urine specific gravity
DI is due to a deficiency of what hormone or peripheral resistance to what?ADH (also known as arginine vasopressin (AVP) or peripheral resistance to ADH
The incidence of DI in the US is 1/________? What gender is more affected?25,000; equally affected
What are the broad classifications and their relation to the cause of each classification?1) central due to ADH deficiency. 2) peripheral/nephrogenic due to ADH resistance
What is the central classification etiology?ADH deficiency
What is the peripheral/nephrogenic classification etiology?ADH resistance
Central DI is classified as primary and secondary. State the difference between primary and secondary?1) primary - there is no identifiable pituitary or hypothalamic lesion. 2) secondary - results from damage to the pituitary or hyptothalamus caused by tumors, neurological infections,autoimmune disorders, and sarcoidosis, neurological procedures, head trauma
What percentage of patients undergoing a transsphenoidal pituitary adenoma resection develop central DI?10-20%
What percentage of patients undergoing neurological resection of a large tumor develop central DI?60-80%
A significant number of individuals sustaining head trauma and traumatic brain injury (TBI) from MVAs and combat related explosive injuries develop what condition?post traumatic diabetes inspidus (PTDI)
What is the prevalence of PTDI?3-50%
What is the mechanism of the development of PTDI due to ?due to a rotational force on the brain imparted by impact, causing trauma to vessels or tethered neurons at the base of the pituitary
Are pressure changes commonly associated with improvised explosive devices (IED) detonations, responsible for PTDI?no
Why is diagnosis of PTDI in the first few hours difficult?because of the likelihood of multiple injuries and impaired consciousness associated with head trauma
PTDI may develop within ____ to _____ hours post-trauma?1-3 hours
What is the significance if PTDI develops earlier?the greater the risk of mortality
If PTDI is treated aggressively initially, what is the survival rate?good and in some cases PTDI may be transient
What is the treatment of PTDI?fluid resuscitation, maintenance of electrolyte balance, use of desmopressin ( DDAVP)
While the majority of cases of PTDI resolve spontaneously, how are those that persist with chronic symptoms treated?the same as other primary or secondary central DI patients and that is with oral or intranets desmopressin
Why is oral desmopressin a good option vs the intranasal preparation?the oral preparation has reduced bioavailability compared to intranasal prep and has superior antidiuretic effect
Why is yearly monitoring needed?to determine the ongoing need for hormone treatment
What causes peripheral/nephrogenic DI?ADH resistance in the renal tubules
What are the two causes of ADH resistance?congenital or acquired
List the causes of acquired ADH resistance?Shogren's syndrome, pyelonephritis, myeloma, chronic hypercalcemis, sickle cell anemia, medication side effects such as from lithium
Is familial DI rare?yes
90% of familial DI cases result from what?x-linked defect in the gene for AVP receptor 2
A mutation of the AVP2 gene causes what?an autosomal dominant variant of nephrogenic DI
Gestational DI is a rare form of DI, which classification does it fall into? What is the cause of gestational DI?1) does not fall into either classification. 2) due to destruction of ADH rather than hypothalamic / posterior pituitary damage
ADHf is the main determinant of ______ water excretion?free
What does ADH do to the kidney?it alters the cortical and medullary collecting tubules' water permeability in the kidney. The hypertonic interstitial fluid in the kidney creates an osmoti. Equilibrium so free water can return to the systemic circulation.
List the two receptors that influence the effects of ADH?1) V1 affects corticotrophin release, prostaglandin synthesis and vasoconstriction. 2) V2 mediates the antidiuretic response
Patients presenting with what clinical signs should have an assessment for DI?dehydration and polyuria particularly if the urine is dilute (specific gravity < 1.005)
*** Because diabetes mellitus also presents with dehydration and polyuria, what lab should be measured.glucose
What other labs should be done?serum electrolytes (which could often reveal hypernatremia) and renal function testing
What imaging study should be done if central DI is suspected?MRI of pituitary and hypothalamus
What test is done to confirm central DI? What do the result reveal? 1) administering vasopressin in a controlled setting and monitoring urine volume and serum electrolytes. 2) patients with central DI show improvement in thirst and polyuria with correction of the underlying defect (absent ADH) while patients with peripheral / nephrogenic DI will not improve due to the complete or relative insensitivity to ADH
*** What is the treatment of choice for central DI (other than correcting underlying conditions)?synthetic desmopressin
Why is synthetic if desmopressin useful in gestational DI?because synthetic vasopressin is not subject to degradation by the process that inactivated naturally occurring vasopressin
What are the formulations for administering desmopressin?intranasal, oral, intramuscular, intravenous
Both central and peripheral DI may improve with what medication?thiazide diuretic HCTZ (Hydrodiuril)
What diet is recommended for nephrogenic DI?low sodium / low protein
If polyuria persists, the sequential addition of what medications is recommended?HCTZ, indomethacin (Indocin) and finally desmopressin
*** SUMMARY = DI is a disorder characterized by what symptoms?polyuria and dehydration unrelated to glucose abnormalities
*** SUMMARY = What is DI caused by?a central deficiency of antidiuretic hormone or a peripheral resistance to that posterior pituitary hormone
*** SUMMARY = Treatment of central DI is what?synthetic desmopressin (DDAVP)
*** SUMMARY = List the causes of central DI?congenital (rare) or acquired forms related to trauma, pituitary surgery, neoplasms, autoimmune disorders or sarcoidosis