Seasonal variations in <scp>TSH</scp> serum levels in athyreotic patients under L‐thyroxine replacement monotherapy

Abstract

Athyreotic patients undergoing L-T4 monotherapy have abnormal seasonal variations in TSH. These changes are secondary to the FT4 and FT3 serum decreases in winter, which occur in spite of the constant treatment. The underlying mechanisms are unclear, but in some cases, these changes may be clinically relevant.