Brief Answer:
Low TSH indicates over replacement

Detailed Answer:
Good day,
Noted your concern. If you have total thyroidectomy, you will need full replacement dose of thyroxine. May i know your weight please?

TSH of 0.21 is little on the lower side and indicates over replacement. That is the reason why your doctor reduuced the dose of synthroid .
Please recheck TSH after 6 weeks on new dose
Regards
Binu

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Brief Answer:
You may have some thyroid tissue left behind

Detailed Answer:
Thank you for the reply. If you are 170 lbs, then your total requirement would be approx 120 mcg daily of synthroid. If you are requiring a smaller dose, that means, you still have some thyroid tisue left behind in your neck on the operated site. I often come across this scenario. An ultrasound may show some thyroid tissue in your neck.

Once the dose has been modified, it takes around 6 weeks for the TSH to stabilize and that is the best time to recheck again.
It is not good to cut down the dose too much at a time,

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Brief Answer:
Viable thyroid cells in neck

Detailed Answer:
May i know what was the indication of idoine ablation ( Grave's disease?).
There is something called "Thyroid stunning" by radio idoine ablation. You have required 2 doses of iodine ablation and still didnt become normal or hypothyroid and required a surgery. This means that, your thyroid cells were not fully killed by the radio idoine doses. Rather, some of the thyroid tissues would have been stunned by radio idoine. These tissues can recover their function gradually over a period of time and start secreting thyroid hormone again. If the surgery didnt remove all the thyroid tissues, gradually the left over thyroid tissues will recover from the previous stunning and start secreting. This is my "hypothesis". This would explain your situation.

As i explained earlier, an ultrasound of neck will probably give an answer. If it shows thyroid tissue in neck with normal vascularity, that means those thyroid cells are still viable and would be secreting atleast some Thyroid hormone. However, i must say that many of these cells eventually die from previous exposure of radio iodine and in that case, in future, the requirement of thyroxine can go up.

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Brief Answer:
Multinodular goiter

Detailed Answer:
Okay. It means the thyroid cells were not fully killed by two ablations. It probably was due to either mutation in the multinodular goiter or due to large volume of thyroid cells in multi nodular goiter. From the history so far, I suspect you may have some small thyroid tissue in neck area which is still secreting small amount of hormone.

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