Apparently TSH measurement is of little use in the diagnosis of secondary hypothyroidism where the origin of the condition lies with pituitary or hypothalamus. TSH levels can be within the normal range or slightly elevated.
It must be rare, but if anyone does have it would be valuable to know how they were diagnosed.
I don't but this is a link which may help.
thyroiduk.org.uk/tuk/about_...
excerpt
The Guidelines also state, "if clinical details are not available that allow the identification of the above categories of patient, then it may be prudent for laboratories to measure serum TSH and FT4 on all specimens rather than embark on a first-line serum TSH testing strategy followed by a cascade to include FT4 and FT3 if indicated."
Unfortunately, in our experience, many doctors are not aware of either the rarer forms of hypothyroidism or these particular sections of the Guidelines. Therefore, it might be an idea to discuss the Guidelines with your GP.
This is a very significant part of the argument against TSH being used for screening and initial testing.
Although doctors appear to think of the pituitary as either working or not working (rather than, maybe, 10% or 50% down on capacity), it is recognised that some degree of pituitary malfunction is fairly common. Have a look for autoimmune hypopituitary.
Rod
I think that although I started off with primary hypothyroidism, where thyroxine alone worked quite well, and still does for my sisters, somewhere along the way I developed secondary and/or pituitary started to slow down too. Yes TSH test is a complete waste with me, especially now I am taking T3, but I am blue in the face trying to explain this to my GP.
Secondary hypothyroidism?
Discrimination against central/secondary hypothyroidism 
secondary hypothyroidism
HYPOTHYROIDISM SECONDARY 
Secondary hypothyroidism 
