This paper is interesting in its own right - suggesting that thyroid hormone dosing maybe could reduce over time whilst continuing to achieve TSH suppression. It is also to interesting to consider what possible impact it could have on those who already tend to have a lower TSH than would be expected, on those with low or suppressed TSH due to T3, and so on.
Horm Metab Res. 2014 May 27. [Epub ahead of print]
The Thyroid Axis 'Setpoints' are Significantly Altered After Long-Term Suppressive LT4 Therapy.
Verburg FA1, Mäder U2, Grelle I1, Visser TJ3, Peeters RP3, Smit JW4, Reiners C1.
1Department of Nuclear Medicine, University of Würzburg, Würzburg, Germany.
2Comprehensive Cancer Center, University of Würzburg, Würzburg, Germany.
3Department of Internal Medicine, Erasmus University Medical Center, Rotterdam, The Netherlands.
4Department of Internal Medicine, University Medical Center St. Radboud, Nijmegen, The Netherlands.
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.
© Georg Thieme Verlag KG Stuttgart · New York.
Image: Ludwigsbrücke (Löwenbrücke) in Würzburg. 2 May 2006 Author Tors - no relevance except the town!