Exp Clin Endocrinol Diabetes 2018; 126(09): 546-552
DOI: 10.1055/s-0043-125064
Article
© Georg Thieme Verlag KG Stuttgart · New York

Symptomatic Relief is Related to Serum Free Triiodothyronine Concentrations during Follow-up in Levothyroxine-Treated Patients with Differentiated Thyroid Cancer

Rolf Larisch
1  Department of Nuclear Medicine, Klinikum Lüdenscheid, Paulmannshöherstr. 14, 58515 Lüdenscheid, Germany
,
John E M Midgley
2  North Lakes Clinical, 20 Wheatley Avenue, Ilkley LS29 8PT, UK
,
Johannes W Dietrich
3  Medical Department I, Endocrinology and Diabetology, Bergmannsheil University Hospitals, Ruhr University of Bochum, Buerkle-de-la-Camp-Platz 1, 44789 Bochum, Germany
4  Ruhr Center for Rare Diseases (CeSER), Ruhr University of Bochum and Witten/Herdecke University, Alexandrinenstr. 5, 44791 Bochum, Germany
,
Rudolf Hoermann
1  Department of Nuclear Medicine, Klinikum Lüdenscheid, Paulmannshöherstr. 14, 58515 Lüdenscheid, Germany
› Author Affiliations
Further Information

Publication History

received 01 September 2017
first decision 23 October 2017

accepted 14 December 2017

Publication Date:
02 February 2018 (eFirst)

Abstract

Aim Patients on levothyroxine-treatment frequently have complaints although TSH is within the reference range. Moreover, FT3 is often low in these patients. The clinical significance of this disequilibrium is studied here.

Patients, methods We conducted a retrospective longitudinal study including 319 patients with differentiated thyroid carcinoma on LT4-medication (1.8 [1.6,2.1] µg/kg body weight). Patients were followed at 2309 visits for at median 63 [46,81] months. Association of reported complaints during follow-up with changes in thyroid parameters were analysed using a generalised linear mixed model accounting for within-variability and intra-subject correlations.

Results 26% of patients expressed hypothyroid and 9.7% hyperthyroid complaints at any one visit, rates per visit being 6.5% and 2%, respectively. During follow-up, median changes in spans were as follows, LT4-dose 0.49 [IQR 0.29,0.72] µg/kg, FT3 1.77 [1.25,2.32] pmol/l, FT4 9.80 [6.70,12.8] pmol/l and TSH 1.25 [0.42,2.36] mIU/l. While rates of both hypothyroid or hyperthyroid symptoms were significantly related to all three thyroid parameters, the relationship of hypothyroid symptoms with FT3 extended to a below reference TSH range. Hypothyroid symptom relief was associated with both a T4 dose giving TSH-suppression below the lower reference limit and FT3 elevated further into the upper half of its reference range. In multivariable analysis, relationships between complaints and FT3 concentrations remained significant after adjusting for gender, age and BMI.

Conclusion Residual hypothyroid complaints in LT4-treated patients are specifically related to low FT3 concentrations. This supports an important role of FT3 for clinical decision making on dose adequacy, particularly in symptomatic athyreotic patients.