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Old 10-31-2011
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Thyroid The concept of high and low radioactive Ioding uptake!

I really dont understand the CONCEPT behind RAI uptake scan being high in graves and toxic nodular but low in subacute thyroiditis, factitious and secondary hypothyroid.
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Old 10-31-2011
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Okay so this is how i simpfy this subject for me...
In Graves Disease what you have is thyroid gland over activity because of Antibodies..so what does this gland needs in order to work ?
Its Iodine ryt ? So when you are giving a radiolabeled Iodine the scan will show increase upake because the gland needs more iodine to work so you end up with the increased up take.

For factitious you are giving exogenous Hormones so the gland is'nt hyperfunctioning it self, abd hence the decreased uptake..
This is how i see it i hope it could e helpful for you
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Old 10-31-2011
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Good explanation for your question here
Radioactive Iodine Uptake in Thyroid diseases
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Old 11-01-2011
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Radioactive Iodine Uptake in Thyroid diseases
It's wise to remember that not all cases of hypothyroidism are associated with decreased Iodine uptake and not all cases of hyperthyroidism are associated with increased Iodine uptake.

Examples of hyperthyroidism with increased uptake:
Typically Grave's disease as the autoantibodies stimulate TSH receptor sensitivity enhancing the uptake.
Secondary and tertiary hyperthyoroidism where the elevated TSH levels also stimulate the uptake.
Toxic adenoma in which the overactive adenoma need to take Iodine to support the production of T4.
Example of hyperthyroidism with decreased uptake:
Factitious hyperthyroidism in which the exogenous T4 causes feedback inhibition on the TSH secretion.
Any other exogenous thyroxine sources such as struma ovarii.
Iodine induced thyroid toxicosis.
Release of thyroid hormone by destructive process e.g. temporary hyperthyroidism seen in subacute thyroiditis.
Toxic Nodular Adenoma, the nodule is active (causing hyperthyroidism) but the rest of the gland is with decreased uptake due to suppressed TSH.
Example of hypothyroidism with increased uptake:
Thyroid hormone receptor insensitivity in which the T4 has no peripheral effects (hence the hypothyroidism) and no feedback effects (hence the elevated TSH and increased uptake).
Example of hypothyroidism with decreased uptake:
Hashimoto, De Quervain, and Reidle thyroditis are all associated with decreased Iodine uptake.

Thyroid carcinoma may variable be hyperthyroid/hypothyroid and Cold/Hot on radioactive Iodine uptake tests.
Last edited by rasheed; 02-07-2010 at 02:08 PM.




THANKS ALOT WELL EXPLAINED HERE
I HAVE TO DISSAGREE WITH TOXIC NODULAR BECOZ THERE WOULD BE A NON-DIFFUSE RATHER LOCALIZED INCREASED UPTAKE (of course in case of hot nodule as it is in toxic nudular adenoma)
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muntasha (03-30-2012), sonu.agarwall (11-01-2011)



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