Bone Turnover in Relation to Thyroid-Stimulating Hormone in Hypothyroid Patients on Thyroid Hormone Substitution Therapy.

Background: Bone turnover markers (BTMs) have emerged as a useful tool for monitoring bone remodeling activity in the skeleton, and their serum levels correlate with bone loss rates in osteoporotic and normal individuals. Whether the same holds for other metabolic bone diseases is still subject to discussion. Methods: We analyzed the relation between levels of BTMs and TSH in 79 females on thyroid hormone substitution therapy for hypothyroidism. Based on the reference range for TSH (0.2-4.0 mU/L) in our lab, we assessed BTMs in five different groups of patients based on the following criteria: (1) hypothyroidism (TSH >4.0); (2) TSH in the high normal range (1.0-4.0); (3) TSH in the low normal range (0.2-1.0); (4) TSH below the normal range (0.01-0.2); (5) TSH undetectable (<0.01). We studied the relationship between TSH and four different bone markers: procollagen type 1 N-terminal propeptide (PINP), C-terminal cross-linking telopeptide of type 1 collagen (CTX), osteocalcin (OC), and bone specific alkaline phosphatase (BSAP). In a subgroup of patients, bone mineral density was assessed by a DXA scan. Results: PINP emerged as the most sensitive and dynamic BTM for assessment of bone turnover in this patient group, achieving significant rho values on nonparametric correlation analysis for both TSH (rho -0.47; p=0.0001) and FT4 (rho 0.27; p=0.018). CTX and OC also revealed significant correlations to TSH, albeit with lower rho values (-0.37 and -0.24, respectively). Categorical analysis showed that bone turnover increased significantly, albeit with pronounced interindividual variability for TSH values below the lower limit of normal (0.2 mU/l), with the most severe affected being women exhibiting suppression of TSH. Further analysis of loss rates by DXA in a limited subgroup of patients showed that this was accompanied by accelerated bone loss. Conclusion: PINP is the most sensitive marker of bone turnover in thyroid disorders. TSH values below the lower limit of normal are associated with increased bone turnover and accelerated bone loss, however, with pronounced interindividual variations. Assessment of PINP may be a valuable tool in cases where there is concern about possible adverse effects of thyroid hormone substitution therapy on bone.

Thyroid Signaling Biomarkers in Female Symptomatic Hypothyroid Patients on Liothyronine versus Levothyroxine Monotherapy: A Randomized Crossover Trial.

Background: Levels of thyroid-stimulating hormone (TSH) are believed to reflect degree of disease in patients with hypothyroidism, and normalization of levels is the treatment goal. However, despite adequate levels of TSH after starting levothyroxine (LT4) therapy, 5-10% of hypothyroid patients complain of persisting symptoms with a significant negative impact on quality of life. This indicates that TSH is not an optimal indicator of intracellular thyroid hormone effects in all patients. Our aim was to investigate different effects of LT3 and LT4 monotherapy on other biomarkers of the thyroid signaling pathway, in addition to adverse effects, in patients with residual hypothyroid symptoms. Methods: Fifty-nine female hypothyroid patients, with residual symptoms on LT4 monotherapy or LT4/liothyronine (LT3) combination therapy, were randomly assigned in a non-blinded crossover study and received LT4 or LT3 monotherapy for 12 weeks each. Measurements, including serum analysis of a number of biochemical and hormonal parameters, were obtained at the baseline visit and after both treatment periods. Results: Free thyroxine (FT4) was higher in the LT4 group, while free triiodothyronine (FT3) was higher in the LT3 group. The levels of reverse triiodothyronine (rT3) decreased after LT3 treatment compared with LT4 treatment. Both low-density lipoprotein (LDL) and total cholesterol levels were reduced, while sex hormone-binding globulin (SHBG) increased after LT3 treatment compared with LT4 treatment. The median TSH levels for both treatment groups were within the reference range, however, lower in the LT4 group than in the LT3 group. We did not find any differences in pro-B-type natriuretic peptide (NT pro-BNP), handgrip strength, bone turnover markers, or adverse events between the two treatment groups. Conclusion: We have demonstrated that FT4, FT3, rT3, cholesterol, and SHBG show significantly different values on LT4 treatment compared with LT3 treatment in women with hypothyroidism and residual symptoms despite normal TSH levels. No differences in general or bone-specific adverse effects were demonstrated. This trial is registered with NCT03627611 in May 2018.

Effect of Liothyronine Treatment on Quality of Life in Female Hypothyroid Patients With Residual Symptoms on Levothyroxine Therapy: A Randomized Crossover Study.

Objective: The effects of levothyroxine (LT4)/liothyronine (LT3) combination therapy on quality of life (QoL) in hypothyroid patients former on LT4 monotherapy have been disappointing. We therefore wanted to test the effects of LT3 monotherapy on QoL in hypothyroid patients with residual symptoms despite thyroid stimulating hormone (TSH) values within the reference range. Design: Female hypothyroid patients with residual symptoms on LT4 monotherapy or combination LT4/LT3 therapy received LT3 and LT4 monotherapy, respectively for 12 weeks in a non-blinded randomized crossover study. Methods: Fifty-nine patients aged 18-65 years were included. QoL was assessed using one disease-specific questionnaire (ThyPRO) and two generic questionnaires (Fatigue Questionnaire and SF-36) at baseline and at the end of the two treatment periods. Clinical indices of cardiovascular health (resting heart rate and blood pressure), as well as thyroid tests, were assessed at baseline and at the end of the two treatment periods. Results: After 12 weeks of LT3 treatment, 12 of the 13 domains of the ThyPRO questionnaire (physical, mental and social domains) showed significant improvements. The most pronounced improvements were less tiredness (mean -21 ± 26; P<0.0001) and cognitive complaints (mean -20 ± 20; P<0.0001). LT4 monotherapy exerted minor effects on two domains only (cognitive complaints and impaired daily life). All three dimensions' scores in the Fatigue Questionnaire (physical, mental and total fatigue) improved after LT3 treatment compared to baseline (P<0.001), and in the SF-36 questionnaire 7 of 8 scales showed significantly better scores after LT3 treatment compared to baseline. There were no differences in blood pressure or resting heart rate between the two treatment groups. TSH in patients on LT3 was slightly higher (median 1.33 mU/L (interquartile range (IQR) 0.47-2.26)) than in patients on LT4 (median 0.61 mU/L (IQR 0.25-1.20; P<0.018). Five patients on LT3 dropped out of the study due to subjectively reported side effects, compared to only one on LT4. Conclusions: LT3 treatment improved QoL in women with residual hypothyroid symptoms on LT4 monotherapy or LT4/LT3 combination therapy. Short-term LT3 treatment did not induce biochemical or clinical hyperthyroidism, and no cardiovascular adverse effects were recorded. Further studies are needed to assess the long-term safety and efficacy of LT3 monotherapy. Clinical Trial Registration: ClinicalTrials.gov, identifier NCT03627611.

Effect of Liothyronine Treatment on Dermal Temperature and Activation of Brown Adipose Tissue in Female Hypothyroid Patients: A Randomized Crossover Study.

Background: Thyroid hormones are essential for the full thermogenic response of brown adipose tissue (BAT) and have been implicated in dermal temperature regulation. Nevertheless, persistent cold-intolerance exists among a substantial proportion of hypothyroid patients on adequate levothyroxine (LT4) substitution. Materials and Methods: To assess if skin temperature and activation of BAT during treatment with liothyronine (LT3) differs from that of LT4 treatment, fifty-nine female hypothyroid patients with residual symptoms on LT4 or LT4/LT3 combination therapy were randomly assigned in a non-blinded crossover study to receive monotherapy with LT4 or LT3 for 12 weeks each. Change in supraclavicular (SCV) skin temperature overlying BAT, and sternal skin temperature not overlying BAT, during rest and cold stimulation were assessed by infrared thermography (IRT). In addition, abundance of exosomal miR-92a, a biomarker of BAT activation, was estimated as a secondary outcome. Results: Cold stimulated skin temperatures decreased less with LT3 vs. LT4 in both SCV (mean 0.009°C/min [95% CI: 0.004, 0.014]; P<0.001) and sternal areas (mean 0.014°C/min [95% CI: 0.008, 0.020]; P<0.001). No difference in serum exosomal miR-92a abundance was observed between the two treatment groups. Conclusion: LT3 may reduce dermal heat loss. Thermography data suggested increased BAT activation in hypothyroid patients with cold-intolerance. However, this finding was not corroborated by assessment of the microRNA biomarker of BAT activation. Clinical Trial Registration: ClinicalTrials.gov, identifier NCT03627611.