Thyrotropin-lowering effect of metformin in a patient with resistance to thyroid hormone.

摘要

Recent studies have shown that metformin administered to patients with untreated hypothyroidism or to hypothyroid patients effectively treated with levothyroxine reduces plasma thyrotropin levels, often to subnormal levels, which is not accompanied by the changes in total and free thyroid hormone levels. Interestingly, metformin effect on plasma thyrotropin is not observed if metformin is given to patients with normal thyroid function. To date, the exact mechanism responsible for the decrease in plasma thyrotropin in hypothyroid patients remains unknown. Metformin may change the affinity and/or number of thyroid hormone receptors, enhance gastrointestinal absorption of levothyroxine, produce subtle changes in thyroid hormone protein binding or affect thyroid hormone metabolism. The reported case of a 28-year-old male with resistance to thyroid hormone (RTH) may in part explain this mechanism. RTH is an inherited syndrome characterised by reduced target tissue responsiveness to thyroid hormone action. Subjects suffering from RTH have raised plasma thyroid hormone levels and raised or inappropriately normal thyrotropin levels that respond to TRH and goiter. RTH may be generalized, or limited either to the pituitary or peripheral tissues, and patients with all forms of RTH differ in their clinical presentation.