If your thyroid hormones are low they will put you on hormone replacement therapy.
Supplementing with 200 microgram/day of Selenium can also be beneficial (2).
Overall, this condition can usually be controlled effectively, and I would expect performance improvements following the initiation of therapy.
(1) Beckett GJ, Arthur JR. “Selenium and endocrine systems.” J Endocrinol. 2005 Mar;184(3):455-65.