diabet insipid - mcris

[ArchivalUser]

Why should I do a water deprivation test to diferentiate diabet insipid from psychogenic polidipsia since one is hyper and the other one is hyponatremic

[ArchivalUser]

psychigenic polidispia is normo or hyponatremic, ( sorry for the above ) .

[ArchivalUser]

nice q

[ArchivalUser]

"Central diabetes insipidus must be distinguished from other causes of polyuria. Therefore, Cushing's syndrome as well as glucocorticoid therapy, diabetes mellitus, drugs (carbamazepine, lithium), psychogenic polydipsia, central nervous system sarcoidosis, as well as intravenous fluid administration must be considered (3). Psychogenic water drinking can be extremely difficult to distinguish from DI. Withholding water from such patients will often result in anxiety, but withholding water from patients with DI, is dangerous. Thus, until the diagnosis can be confirmed, an evaluation for DI in uncertain cases, must often be done as an inpatient to establish the diagnosis. In theory, psychogenic water drinkers should not have hypernatremia. "

http://www.hawaii.edu/medicine/pediatric...15c05.html

[ArchivalUser]

u water deprive the pt,,, see urine osmolarity,,, in psychogenic pt they do not have problom the result will decrease in the urine out put + increase in the urine concentration. what happens is that the ADH homone inserts its water channels in the collecting tubules absorbing more and more water.
but in DI if the subject is water getting water deprived no matter how severe no water will be reabsorbed in collecting duct what happens u will the pt loosing water like crazy, causing severe hypertonic water deprivation making dilute hypotonic urine.
here is tow scenario,,, either the pt is not making ADH (central) meaning if we provide pt with ADH they will happily stick to the tubules. So if we gave pt the ADH in this taste and urine volume decreases with proper salt amount in it. THE nephrogenic cause is R/o.
otherwise if we supply pt with ADH and he is still passing dow diluted volumous urine. it means the pt does not have problem with the ADH secretion but his tubules for some crazy reason can't sense the existance of ADH in circulation. Here u have to get rid of excessive salt accumulated in the body so Tx is loop diuritic,,, because it makes your urine hypertonic and that is what we exactly want here.

[ArchivalUser]

but some how the q is not answered

di has always hypernatremia

psychogenic polydypsia has never hypernatrmia

when the picture is just opposite then why you need to do do water deprivation test . in respect tto di let us not talk siadh in this comparison

[ArchivalUser]

but if you see from water intake&loss perspective they are not opposit and hyper and nl can give same clinical picture only after water deprivation we can reach the coclusion of hypo and hyper natremia. In another word if you don't do water deprivation test both pt's lab is eunatremic,,,di pt takes too much water to ballance the loss of water so he has to add enough water to keep hardly his salty body fluid iso. In second case pt's body fluid is iso but for some crazy reason he does not like this combosition and wants it to be hypotonic by drinking unnecessary water but again here ADH does not allow his psychogenic urge to change the homeostasis. So here again body Na is stable. Now when the pt come and say sorry I am drinking too much and peeing too much, and after thourough investigation u know if the pt is hyper or iso. So u need this test as only way to d/d these two that though opposit have same clinical picture (not as u said Opposit pictur).

[ArchivalUser]

thanks

now tell me who came first mother or daughter

then tell me who came first chicken or egg

just kidding

i understood your explanation

i appreciate it

[ArchivalUser]

yessss,,, and now u got me,,, here water comes first then you get to the hypo/hypernatremia,,,
but that was actually very intellegent q, and thank you for sharing such thought provoking q, honestly i did not saw it that way before, this was kind of q that teach u things that u cannot get it by reading tens of pages, and it really shows the knowledge of person that asks it. thanks mcris and drjyoti...

[ArchivalUser]

Yes, this is question that makes you think.