The thyroid axis 'setpoints' are significantly altered after long-term suppressive LT4 therapy.

Abstract

The aim of the study was to investigate the changes in the thyroid axis setpoint after long-term suppressive levothyroxine therapy for differentiated thyroid carcinoma and the resulting changes in levothyroxine requirement. Ninety-nine differentiated thyroid cancer patients were reviewed. All patients had at least one known TSH-level≥0.01 mU/l (lower detection limit) and <1.0 mU/l within 2 years of initial treatment (time 1) and had at least one TSH-value≥0.01 mU/l and <1.0 mU/l after continuous LT4 therapy for a minimum of 5 years (time 2).At time 2 the mean LT4 dosage/kg body weight, TSH, FT3, and FT4 levels were significantly lower than at time 1, while body weight was higher. At time 2, the FT3/FT4 ratio rate had dropped significantly (p<0.001). At time 1, patients would require 2.96 μg/kg body weight to reach total TSH suppression. The dose of levothyroxine/kg required for suppression can be lowered by about 0.05 μg/kg body weight for each year of suppressive therapy. After a median of 12.7 years of continuous suppressive levothyroxine therapy, patients would require 2.25 μg/kg body weight (-23.5%) to reach total TSH-suppression. At least part of this reduction was independent of aging. As a result of changes in thyroid hormone metabolism and thyroid axis setpoint, long-term TSH-suppressive therapy contributes to a reduction in the dosage of levothyroxine per kilogram body weight required for full TSH suppression over time.

• Authors: F A Verburg, U Mäder, I Grelle, T J Visser, R P Peeters, J W A Smit, C Reiners
• Journal: Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme (Horm Metab Res) Vol. 46 Issue 11 Pg. 794-9 (Oct 2014) ISSN: 1439-4286 [Electronic] Germany
• PMID: 24867137 (Publication Type: Journal Article)
• Copyright: © Georg Thieme Verlag KG Stuttgart · New York.

Chemical References

• Triiodothyronine
• Thyrotropin
• Thyroxine

Topics

• Adolescent
• Adult
• Age Factors
• Aged
• Aged, 80 and over
• Body Weight (drug effects)
• Female
• Follow-Up Studies
• Humans
• Male
• Middle Aged
• Thyroid Gland (drug effects, metabolism)
• Thyrotropin (metabolism)
• Thyroxine (metabolism, pharmacology)
• Triiodothyronine (metabolism)
• Young Adult