"The thyroid‚Äôs circadian pattern is diminished in autoimmune hypothyroidism. In a study of hypothyroid children, the night-time surge of TSH averaged 22%, compared to 124% in normal children."
It's more and more what I keep thinking... hypothyroidism comes from the brain. So the pituitary is not active enough at night. Now if you traced this further, they should have looked at the TRH. If it was also low, that would confirm that the hypothalamus is malfunctioning as well. Something happens that reprograms the thyroid to work at a lesser level and it comes straight from the brain. The thyroid could work just fine, in most people without autoimmune hypothyroidism it's not damaged. But for some reason, it's being told NOT to work at full capacity. This is why it's such a b**** to treat hypothyroidism, and maybe why people stay dependent on meds. The root cause is somewhere up there.
EDIT: It seems they looked at the TRH and it was mostly normal. So it seems that the pituitary does not respond to the TRH adequately at night. This is interesting.