Pituitary resistance to thyroid hormone

Pituitary resistance to thyroid hormone (also known as selective pituitary resistance to thyroid hormone, or isolated pituitary resistance to thyroid hormone) is a rare endocrine disorder in which the pituitary gland has a reduced sensitivity to the inhibitory effects of thyroid hormones, while peripheral tissues retain relatively normal responsiveness. This condition is considered a selective form of resistance to thyroid hormone (RTH), where the defect is predominantly localized to the pituitary thyrotroph cells. As a result, the pituitary continues to secrete thyroid-stimulating hormone (TSH) despite elevated circulating levels of free thyroxine (T4) and triiodothyronine (T3), leading to a biochemical picture of inappropriately normal or elevated TSH with high thyroid hormone levels. Clinically, patients may present with signs and symptoms of thyrotoxicosis (hyperthyroidism) in peripheral tissues, including tachycardia, weight loss, tremor, anxiety, heat intolerance, and goiter, because the peripheral organs respond normally to the excess thyroid hormones driven by persistent TSH secretion. This distinguishes pituitary resistance from generalized resistance to thyroid hormone, where peripheral tissues are also resistant and patients may appear clinically euthyroid or even hypothyroid. The condition must be carefully differentiated from TSH-secreting pituitary adenomas (thyrotropinomas), which can present with a similar biochemical profile. Most cases of pituitary resistance to thyroid hormone are associated with mutations in the thyroid hormone receptor beta (THRB) gene, similar to generalized resistance to thyroid hormone, though the phenotypic expression is predominantly pituitary. Management is challenging and must be individualized. Treatment strategies may include the use of thyroid hormone analogs such as triiodothyroacetic acid (TRIAC) to suppress TSH secretion, beta-blockers to manage peripheral hyperthyroid symptoms, or in some cases, careful use of antithyroid drugs. There is no definitive cure, and long-term monitoring of thyroid function and clinical symptoms is essential.

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