In certain benign tumors of the pituitary gland that overproduce TSH, the lack of thyroid hormone receptors prevents thyroid hormone from signaling the tumor to stop releasing TSH, leading to elevated thyroid hormone levels alongside abnormally high TSH.

In tumors that produce excess TSH hormone, the proteins that respond to thyroid hormones are not detectable, even though the genetic instructions to make them are present. This suggests a problem in converting those instructions into functional proteins, which could disrupt the body's normal control of TSH levels.

In certain pituitary tumors that overproduce TSH, the genetic instructions for thyroid hormone receptors are present and readable, but the receptors themselves are not made, suggesting a problem occurs after the genetic code is copied but before the protein is assembled.

In people with thyrotoxicosis caused by taking too much thyroid hormone medication, the brain's control system for thyroid hormone levels behaves differently than in people whose thyroid gland overproduces hormones on its own. Specifically, TSH stays low even when thyroid hormone levels are higher than normal.

Kids can have an overactive thyroid even if their TSH blood test looks normal, especially if they have a small overactive lump in the thyroid that makes hormones on its own.

All premenopausal women with a certain type of thyroid tumor have very low levels of a key hormone (TSH), no matter how severe their thyroid symptoms are — but that low hormone level alone doesn’t tell us if their bones are being affected.