TSH Level in central hypothyroidism? - USMLE Forums
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Old 09-15-2011
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Thyroid TSH Level in central hypothyroidism?

Can central hypothyroidism have low T4, normal TSH and normal T3?
I think central hypothyroidism is same as tertiary/secondary hypothyriodism which is due to hypothalmus/pituitary dysfxn giving low TSH, low T4 and T3 doesn't matter much as it decreases at later stage of hypothyroidism
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Old 09-15-2011
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Default It can be normal and even high!

The diagnosis of central hypothyroidism requires measurement of both serum free T4 and TSH. In patients with central hypothyroidism, serum free T4 is low or low-normal, but serum TSH may be low, normal, or even slightly elevated.
Normal or high serum TSH concentrations in some patients with central hypothyroidism is due, in part, to the secretion of TSH that has reduced biologic activity but normal immunoactivity. Reduced bioactivity is due to abnormalities in glycosylation of the TSH subunits, which is under the control of TRH.
There is a diurnal rhythm in TSH secretion, with a surge late in the evening. This appears to be under hypothalamic control, and is absent in many patients with central hypothyroidism [24,25]. Thus, TSH measurements may be normal during the daytime, but the absence of a nocturnal rise in TSH reduces the overall quantity of TSH secreted by the pituitary gland, causing clinical hypothyroidism.

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Old 09-16-2011
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Originally Posted by Hokolesqua View Post
The diagnosis of central hypothyroidism requires measurement of both serum free T4 and TSH. In patients with central hypothyroidism, serum free T4 is low or low-normal, but serum TSH may be low, normal, or even slightly elevated.
Normal or high serum TSH concentrations in some patients with central hypothyroidism is due, in part, to the secretion of TSH that has reduced biologic activity but normal immunoactivity. Reduced bioactivity is due to abnormalities in glycosylation of the TSH subunits, which is under the control of TRH.
There is a diurnal rhythm in TSH secretion, with a surge late in the evening. This appears to be under hypothalamic control, and is absent in many patients with central hypothyroidism [24,25]. Thus, TSH measurements may be normal during the daytime, but the absence of a nocturnal rise in TSH reduces the overall quantity of TSH secreted by the pituitary gland, causing clinical hypothyroidism.

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so if TSH could be normal or even high, how do we differentiate it from pri hypothyriodism?? atleast in exam??
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Old 09-16-2011
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Originally Posted by aasiaafzal View Post
so if TSH could be normal or even high, how do we differentiate it from pri hypothyriodism?? atleast in exam??
I think we have to rely on clinical features for that....
Also keep in mind the sick euthyroid syndrome, where u get low T3 & T4 with normal TSH levels.
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Old 09-16-2011
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Originally Posted by step1an View Post
I think we have to rely on clinical features for that....
Also keep in mind the sick euthyroid syndrome, where u get low T3 & T4 with normal TSH levels.
u r right about the clinical features but selecting sec hypothyriodism would be very difficult for me, with high tsh even if they keep on saying pt has hemianopia...!!!
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