Endocrine Abstracts

Introduction: Thyroid hormone (TH) replacement therapy in patients with central hypothyroidism (CHT) cannot be reliably guided by TSH levels. Guidelines suggest substitution doses between 1.2–1.6 µg/kg body weight, aiming for free thyroxine levels (fT4) prior to intake in the upper part of normal. However, variability in TH metabolism, concomitant treatments and inaccurate interpretation of TSH levels still puts patients with CHT at risk for inappropriate substitution as compared to patients with primary hypothyroidism (PHT).

Objective: To compare levothyroxine substitution doses between patients with CHT and PTH, and to explore Quality of Life (QoL) in both groups, using two questionnaires, the SF-36 health score and the thyroid specific ThyPRO score.

Methods: This is a monocentric, cross-sectional study, performed at the Ghent University Hospital (Belgium). During 12 months, we consecutively included 70 patients, 41 patients with CHT and 29 patients with PHT. At the time of inclusion, all patients had to have a stable dose of levothyroxine during the past six months and patients with PHT needed to be euthyroid (defined as a TSH level within the reference range, 0.2–4.5 mU/l). Patients with malabsorptive disorders, malignancies or conditions affecting TH metabolism or dosing were excluded. All data was retrieved from medical files, timing of blood sampling was not specifically instructed, questionnaires were self-administered.

Results: Patients from the CHT and PHT group were comparable regarding age and BMI. There were no significant differences between patients with CHT and PHT regarding absolute dose of levothyroxine (100 [93.75–125.00] vs 107.14 [81.25–132.14] µg/day, P = 0.942) or dose relative to body weight (1.34 [1.16–1.55] vs 1.51 [1.14–1.73] µg/kg/day, P = 0.265). Individual doses, however, varied substantially (0.71–2.44 in CHT and 0.48–2.56 µg/kg/day in PHT). Randomly sampled serum levels of fT4 and fT3 did not differ between the two groups (P = 0.269 and P = 0.132, respectively) and were in the midrange for both groups. We could not demonstrate differences between both groups regarding QoL questionnaires.

Conclusion: In our patients with CHT, median levothyroxine dose was within the suggested range and although numerically somewhat lower not significantly different from patients with PTH. We neither found differences in QoL between both groups. Interindividually, however, substitution doses varied substantially in both groups, so an individual appraisal of every patient is warranted rather than a one-size-fits-all approach.