hero wrote:
according to UW, unexplaned hyponatremia is indication for thyroid testing bcs it may occur in hypothyroid pts due to inappropriat ADH secretion.
Can't get this concept, is there any idea what it is about?
I'm guessing and thinking logically.. so here it goes....
Hypothyroid (decreased Thyroid hormone) -loss of Negative feedback to the pituitary, and thus INCREASED TSH from the pituitary. Since this Neg. FB occurs at the level of the pituitary, could ADH also be increased?
I have read that in SEVERE Hypothyroidism, TSH and TRH will be high, so a VERY HIGH TRH can actually stimulate the release of Prolactin from the pituitary...
So maybe this is the same concept for ADH.... What do you think?
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| equinoxe
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Euvolaemic hyponatraemia can be caused by:
- inappropriate SIADH
- adrenal insufficiency
- hypothyroidism
Pseudohyponatraemia is indicated by:
- elevated triglyceride or protein levels
- iso-osmolar plasma (280-300mOsmol/L)
Redistributive hyponatraemia is indicated by:
- elevated glucose or mannitol levels
- hyperosmolar plasma (more than 300mOsmol/L)
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| DrVirgo
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equinoxe wrote:Euvolaemic hyponatraemia can be caused by:
Yes, thats true but the question here is HOW??? What's the mechanism.
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| docnikki
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I remember from step 1 physiology that thyroid hormones have an inhibhitory effect over ADH...so in hypothyroid condition obviusly ADH will rise high and lead to hyponatremia.
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| equinoxe
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My impression was that it is "somehow" due to the edematous state of hypothyroidism. I've checked Harrison 16 Hyponatremia (p255)
"The mechanisms by which hypothyroidism leads to hyponatremia include
decreased cardiac output and GFR and increased AVP secretion in
response to hemodynamic stimuli."
In CMDT at hyponatremia also mentiones that altough rare, in hypothyroidism hyponatremia can reach <110 due to increased ADH.
"Hyponatremia is not commonly caused by hypothyroidism, but it can occur on occasion with serum sodium levels as low as 110 mEq/L. Water retention is the cause, probably both from inappropriately elevated ADH levels and from alterations in the handling of water by the kidneys."
Edited by equinoxe on 02/09/08 - 11:37 AM
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| DrVirgo
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Good explanation equinoxe!  Thanks for looking it up.
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