Thyroid antibodies and levothyroxine effects in subclinical hypothyroidism: A pooled analysis of two randomized controlled trials

BACKGROUND

Antithyroid antibodies increase the likelihood of developing overt hypothyroidism, but their clinical utility remains unclear. No large randomized controlled trial (RCT) has assessed whether older adults with subclinical hypothyroidism (SHypo) caused by autoimmune thyroid disease derive more benefits from levothyroxine treatment (LT4).

OBJECTIVE

To determine whether older adults with SHypo and positive antibodies derive more clinical benefits from LT4 than those with negative antibodies.

METHODS

We pooled individual participant data from two RCTs, Thyroid Hormone Replacement for Untreated Older Adults with Subclinical Hypothyroidism and IEMO 80+. Participants with persistent SHypo were randomly assigned to receive LT4 or placebo. We compared the effects of LT4 versus placebo in participants with and without anti-thyroid peroxidase (TPO) at baseline. The two primary outcomes were 1-year change in Hypothyroid Symptoms and Tiredness scores on the Thyroid-Related Quality-of-Life Patient-Reported Outcome Questionnaire.

RESULTS

Among 660 participants (54% women) ≥65 years, 188 (28.5%) had positive anti-TPO. LT4 versus placebo on Hypothyroid Symptoms lead to an adjusted between-group difference of -2.07 (95% confidence interval: -6.04 to 1.90) for positive antibodies versus 0.89 (-1.76 to 3.54) for negative antibodies (p for interaction = 0.31). Similarly, there was no treatment effect modification by baseline antibody status for Tiredness scores-adjusted between-group difference 1.75 (-3.60 to 7.09) for positive antibodies versus 1.14 (-1.90 to 4.19) for negative antibodies (p for interaction = 0.98). Positive anti-TPO were not associated with better quality of life, improvement in handgrip strength, or fewer cardiovascular outcomes with levothyroxine treatment.

CONCLUSIONS

Among older adults with SHypo, positive antithyroid antibodies are not associated with more benefits on clinical outcomes with LT4.

Evaluation of Weight Gain, Clinicopathological and Radiographic Changes after Early Diagnosis and Treatment of Congenital Hypothyroidism in Cats

Congenital hypothyroidism is uncommon in cats. This case report describes weight gain, clinicopathological and radiographic changes after early diagnosis and treatment of congenital hypothyroidism in three British shorthair cats’ siblings. Data were assessed at 53 (diagnosis), 83, 185 and 365 days of age. Correlations between serum insulin-like growth factor-1 (IGF-1) and body weight, levothyroxine dose, total thyroxine, and thyroid-stimulating hormone concentrations were evaluated. The body weights of the congenital hypothyroid kittens were compared with those of their two healthy siblings and British shorthair kittens of the same age. At diagnosis, the congenital hypothyroid kittens showed a significantly lower body weight compared to the healthy siblings (p = 0.03). After diagnosis, oral levothyroxine supplementation was started. The difference in body weight was no longer observed after one month of treatment. The clinical signs, clinicopathological and radiographic abnormalities ameliorated after one month of treatment. IGF-1 concentration was significantly positively correlated with body weight (rs = 0.80, p < 0.002). In conclusion, resolution of the clinical signs, achieving a consistent within-breed weight, and improvement of the clinicopathological and radiographic parameters demonstrated the importance of the early diagnosis and treatment of feline congenital hypothyroidism.

Severe Resistance to Thyroid Hormone Beta in a Patient with Athyreosis

We report a patient with congenital hypothyroidism due to athyreosis complicated by a heterozygous thyroid hormone receptor beta (THRβ) gene mutation (R320L), resulting in a severe resistance to thyroid hormone beta phenotype. The proband inherited the mutant allele from his father, presenting a very mild phenotype. While the precise reason for this discrepancy remains unknown, we postulate the possibility of de novo mutation and mosaicism in the father. Correlating thyrotropin (TSH) with free thyroxine (fT4) allowed us to predict the amount of fT4 required to normalize the proband's TSH, which supported the treatment with high dose of levothyroxine.

Effect of initial levothyroxine dose on neurodevelopmental and growth outcomes in children with congenital hypothyroidism

OBJECTIVES

We designed a multicentre open prospective randomized trial to evaluate the risk-benefit profile of two different initial treatment schemes with levothyroxine (L-T4), 10-12.5 μg/kg/day vs 12.6-15 μg/kg/day, on growth and neurodevelopmental outcomes in children with congenital hypothyroidism (CH) detected by neonatal screening to identify the best range dose to achieve optimal neurocognitive development.

DESIGN PATIENTS AND METHODS

Children detected by neonatal screening were randomly assigned to receive an initial L-T4 dose of 10-12.5 μg/kg/day (Low) or 12.6-15 μg/kg/day (High). All patients underwent periodical clinical examination with measurement of growth parameters and measurement of TSH and FT4. Neurocognitive development was evaluated at the age of 24 months using Griffiths Mental Development Scales (GMDS) and cognitive and behavioral assessment was performed at 48 months of age using Wechsler Preschool and Primary scale of Intelligence (WIPPSI-III). The study was registered with clinicaltrials.gov (NCT05371262).

RESULTS

Treatment schemes below or above 12.5 μg/kg/day were both associated with rapid normalization of TSH and thyroid hormone levels in most patients with no differences in the risk of over- and under-treatment episodes in the first months of life. Growth parameters were normal and comparable between the two groups. Developmental quotients at 24 months of age were normal in both groups (Low 100.6 ± 15.5 vs High 96.9 ± 16.6). Likewise, at 4 years of age IQ and subtest scores were comparable between patients from Low and High (Total IQ 104.2 ± 11.4 vs 101.0 ± 20.3, Verbal IQ 103.9 ± 11.5 vs 98.7 ± 15.1, Performance IQ 105.3 ± 10.4 vs 100.3 ± 19.8). 6/45 CH patients (13.3%) showed a total IQ below 85 (73.7 ± 5.9) regardless of age at diagnosis, L-T4 starting dose, time of FT4 and TSH normalization and episodes of over and undertreatment. Worse socioeconomic status and delayed bone age at diagnosis were the only predictors of an increased risk of having suboptimal IQ at 24 and IQ at 48 months.

CONCLUSIONS

Our results indicate that initial treatment with L-T4, 10-12.5 μg/kg/day vs 12.6-15 μg/kg/day, are both associated with normal growth and neurodevelopmental outcomes in children with CH detected by neonatal screening. Further studies with a long-term follow-up on a larger number of patients are needed to confirm these results.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT05371262?term=NCT05371262&draw=2&rank=1 identifer NCT05371262.

Thyroid autoimmunity and its negative impact on female fertility and maternal pregnancy outcomes

Thyroid autoimmunity (TAI) is commonly defined as the presence of thyroperoxidase antibodies (TPOAbs) and/or thyroglobulin antibodies (TgAbs), which predisposes an individual to hypothyroidism. TAI affects nearly 10% of women of reproductive age and evokes great interest from clinicians because of its potentially negative impact on female fertility and pregnancy course. In this mini-review, we review the current literature concerning the influence of TPOAb or TPOAb/TgAb positivity without thyroid dysfunction on reproduction. TAI may negatively affect female fertility; several studies have found an increased prevalence of TAI in infertile women, especially in those with unexplained infertility and polycystic ovary syndrome. According to some observations, TAI might also be connected with premature ovarian insufficiency and endometriosis. The relationship between TAI and an increased risk of pregnancy loss is well documented. The pathophysiological background of these observations remains unclear, and researchers hypothesize on the direct infiltration of reproductive organs by thyroid antibodies, co-existence of TAI with other autoimmune diseases (either organ specific or systemic), immunological dysfunction leading to inhibition of immune tolerance, and relative thyroid hormone deficiency. Interestingly, in the current literature, better outcomes of assisted reproductive technology in women with TAI have been reported compared with those reported in earlier publications. One plausible explanation is the more widespread use of the intracytoplasmic sperm injection method. The results of randomized clinical trials have shown that levothyroxine supplementation is ineffective in preventing adverse pregnancy outcomes in women with TAI, and future research should probably be directed toward immunotherapy.

Carotid Intima-Media Thickness in Patients with Subclinical Hypothyroidism: A Prospective Controlled Study

PURPOSE

The association between subclinical hypothyroidism (SCH) and cardiovascular risk, particularly with a TSH <10 µIU/ml, remains controversial. The objective of our study was to assess the association between SCH and cardiovascular risk through carotid intima-media thickness, and alternatively, to evaluate its change after treatment with levothyroxine.

METHODS

A total of 54 individuals were included in the study: 18 with SCH; 18 with overt hypothyroidism (OH); and 18 healthy controls (HC). The carotid intima-media thickness was measured in each group. In SCH, follow-up was performed at three and six months after the start of levothyroxine treatment.

RESULTS

The mean age of the total population at baseline was 35.8 years. The median TSH in SCH was 6.15 µIU/ml. The carotid intima-media thickness (mean and standard deviation) was greater in SCH in comparison to the HC group: right common carotid artery (RCCA), 0.486 ± 0.106 mm and 0.413 ± 0.075 mm in SCH and HC, respectively, p=0.01 and left common carotid artery (LCCA), 0.511 ± 0.144 mm and 0.427 mm ± 0.090 in SCH and HC, respectively, p=0.03). In patients with SCH, there was a decrease in the carotid intima-media thickness after treatment with levothyroxine (RCCA and LCCA, p <0.05 at three and six months).

CONCLUSIONS

There was an association between increased carotid intima-media thickness in patients with SCH in comparison with HC, even with a TSH <10 µIU/ml. The increase was reversed with levothyroxine therapy. The association of this increased thickness with important cardiovascular outcomes remains uncertain and should be evaluated in future studies.

Pregnancy and Neonatal Outcomes With Levothyroxine Treatment in Women With Subclinical Hypothyroidism Based on New Diagnostic Criteria: A Systematic Review and Meta-Analysis

BACKGROUND

Subclinical hypothyroidism (SCH) during pregnancy has been associated with multiple adverse maternal and neonatal outcomes. However, the potential benefits of levothyroxine (LT4) supplementation remain controversial. Variations across studies in diagnostic criteria for SCH may, in part, explain the divergent findings on the subject. This study aimed to assess the effect of LT4 treatment on pregnancy and neonatal outcomes among pregnant women who were diagnosed as SCH based on the most recent diagnostic criteria.

METHODS

We conducted a systematic review and meta-analysis of the literature published from inception to January 2020. The search strategy targeted the studies on pregnancy and neonatal outcomes following LT4 treatment in women with SCH based on 2017 American Thyroid Association diagnostic criteria. Pooled effect sizes were estimated using fixed and random effect models, according to the absence or presence of heterogeneity which was assessed using the I-squared statistic. Sources of heterogeneity and the stability of results were evaluated through sensitivity analysis.

RESULTS

Of the 2781 identified references, 306 full-text articles were screened for eligibility. Finally, 6 studies including a total of 7955 participants were retained for analysis. Summary effect estimates indicated that pregnant women with SCH treated with LT4 had a lower risk of pregnancy loss [odds ratio (OR) = 0.55, 95% confidence interval (CI): 0.43-0.71], preterm birth (OR=0.63, 95% CI: 0.41-0.98) and gestational hypertension (OR = 0.78, 95% CI: 0.63-0.97) than those in control group.

CONCLUSION

LT4 treatment in pregnant women with SCH may reduce the risk of pregnancy loss, preterm delivery and gestational hypertension.

Early Levothyroxine Treatment for Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy: The St Carlos Gestational and Thyroid Protocol

The optimal maternal levels of thyroid hormones (TH) during the first trimester of gestation have not been established, nor has the ideal moment to initiate levothyroxine treatment (LT) to improve the evolution of gestation and fetal development. Cut-off points for Thyroid-stimulating hormone (TSH) <2.5 µIU/mL and free thyroxine (FT4)>7.5 pg/mL have been recommended. There are no data on whether initiation of LT <9th Gestational Week (GW) can have a favourable impact.

OBJECTIVE

To define the TSH/FT4 percentiles corresponding with 2.5 µIU/mL and 7.5 pg/mL levels, respectively, at GW8 (Study 1), and evaluate the effects of protocol-based LT before GW9 on gestation evolution, in women with TSH ≥2.5 µIU/mL and/or FT4≤ 7.5 pg/mL (study 2).

SUBJECTS

2768 consecutive pregnant women attending the first gestational visit from 2013-2014 and 3026 from 2015-2016 were eligible for Study I and 2 respectively. A final 2043 (study 1) and 2069 (study 2) women were assessed in these studies.

RESULTS

Study 1: The FT4 level of 7.5 pg/mL corresponds with the 17.9th percentile, a TSH level of 2.5 µIU/mL with the 75.8^th. Women with TSH ≥2.5 µIU/mL had a history of fetal losses more frequently than those <2.5 (OR 2.33 (95%CI): 1.58-3.12), as did those with FT4 ≤7.5 pg/ml compared to those >7.5 (OR 4.81; 3.25-8.89). Study 2: A total of 1259 women had optimal TSH/FT4 levels (Group 1), 672 (32.4%, Group 2) had suboptimal TSH or T4l, and 138 (6.7%, Group 3) had suboptimal values of both. 393 (58.5%) in Group 2 and 88 (63.8%) in Group 3 started LT before GW9. Mean (SD) GW24 levels were TSH: 1.96 ± 1.22 µIU/mL and FT4: 7.07 ± 1.25 pg/mL. The highest FT4 value was 12.84 pg/mL. The adjusted risk for an adverse event if LT was started early was 0.71 (0.43-0.91) for Group 2 and 0.80 (0.66-0.94) for Group 3.

CONCLUSIONS

Early LT in women with suboptimum levels of TSH/FT4 (≥2.5µIU/mL/≤7.5 pg/ml) at or before GW9 is safe and improves gestation progression. These data support the recommendation to adopt these cut-off points for LT initiation, which should be started as early as possible.

Levothyroxine Replacement Alleviates Thyroid Destruction in Hypothyroid Patients With Autoimmune Thyroiditis: Evidence From a Thyroid MRI Study

Background: Autoimmune thyroiditis (AIT) is the most frequent cause of hypothyroidism. Our previous studies have shown that magnetic resonance T1-mapping is a new technique for quantitatively evaluating the degree of thyroid destruction in AIT patients. This study aimed to evaluate the effect of levothyroxine on thyroid destruction in hypothyroid AIT patients using thyroid T1-mapping technique. Methods: This study recruited 29 hypothyroid AIT patients and 18 age- and sex-matched healthy individuals. Thyroid T1-mapping values were measured in all participants and repeated in the AIT patients at 3 months after they achieved a euthyroid state following levothyroxine treatment. Results: Thyroid T1-mapping values were higher in the AIT patients than in the healthy controls (1167.2 ± 163.2 vs. 779.6 ± 83.8 ms, P < 0.01), and levothyroxine treatment significantly decreased the thyroid T1-mapping values of AIT patients (1006.3 ± 114.6 vs. 1167.2 ± 163.2 ms, P < 0.01). Meanwhile, the reduced levels of anti-peroxidase antibody (TPOAb) and anti-thyroglobulin antibody (TgAb) were observed in the AIT patients after levothyroxine treatment [TPOAb: 257.6 (23.9-960.6) vs. 1,287.4 (12.6-2000.0) IU/mL, P < 0.01; TgAb: 53.54 (9.58-386.2) vs. 103.9 (34.2-1,596.8) IU/mL, P < 0.05]. High-sensitivity C-reactive protein (hsCRP) levels showed a descending tendency following levothyroxine treatment, although there was no statistical difference (P > 0.05). Conclusions: In the AIT patients, thyroid T1-mapping values were significantly increased, and levothyroxine treatment significantly decreased the thyroid T1-mapping values of the AIT patients. These results might suggest that levothyroxine treatment alleviates thyroid destruction in hypothyroid AIT patients.

Levothyroxine supplementation on assisted reproduction technology (ART) outcomes in women with subtle hypothyroidism: a retrospective study

The need for treating subclinical hypothyroidism (SCH) in women undergoing assisted reproduction technology (ART) is under debate. Moreover, it is known that controlled ovarian hyperstimulation (COH) protocols may impair the thyroidal axis. Therefore, we evaluated if levothyroxine (L-T4) supplementation in SCH women before undergoing ART positively affects the main reproductive outcomes. We retrospectively analyzed in vitro fertilization (IVF) data of 4147 women submitted to 6545 cycles in a tertiary care IVF Center (January 2009-December 2014). L-T4 (1.4-2.0 mcg/kg) treatment was offered to all women with a pre-cycle TSH >2.5 mIU/L before starting COH and main ART outcomes were compared in euthyroid and L-T4-treated women undergoing ART. Among 4147 women, 1074 (26%) were affected by SCH and were treated with L-T4 before COH was started. No statistically significant differences among L-T4-treated and euthyroid women group were observed regarding pregnancy rate, respectively, per cycle (27.67% vs 26.37%; p = .314) and per embryo transfer (30.13% vs 29.17%; p = .489), live birth rate, respectively, per cycle (21.58% vs 20.38%; p = .304) and per embryo transfer (23.49 vs 22.54%; p = .449) and the rest of primary and secondary efficacy endpoints. Early L-T4 treatment for infertile women with a subtle thyroid dysfunction may mitigate and protect from the negative effects of SCH in the setting of ART, and may preventively overcome also the negative impact of COH on thyroidal axis.

Effect of Levothyroxine on Blood Pressure in Patients With Subclinical Hypothyroidism: A Systematic Review and Meta-Analysis

Background: Patients with subclinical hypothyroidism (SCH) have elevated blood pressure, but the effect of levothyroxine (LT4) therapy on blood pressure among those patients is still unclear. This study aimed to assess whether LT4 therapy could reduce blood pressure in SCH patients through a systematic review and meta-analysis. Methods: PubMed, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Science were searched. Randomized controlled trials (RCTs) assessing the effect of LT4 therapy on blood pressure or prospective follow-up studies comparing the blood pressure level before and after LT4 treatment were included, and the mean difference of systolic blood pressure (SBP) or diastolic blood pressure (DBP) was pooled using random-effect meta-analysis. Results: Twenty-nine studies including 10 RCTs and 19 prospective follow-up studies were eligible for the analysis. Meta-analysis of 10 RCTs suggested that LT4 therapy could significantly reduce SBP in SCH patients by 2.48 mmHg (95% CI -4.63 to -0.33, P = 0.024). No heterogeneity was observed among these 10 RCTs (I² = 0%). Meta-analysis of the 19 prospective follow-up studies found that LT4 therapy significantly decreased SBP and DBP by 4.80 mmHg (95%CI -6.50 to -3.09, P < 0.001) and 2.74 mmHg (95%CI -4.06 to -1.43, P < 0.001), respectively. Conclusion: The findings suggest that LT4 replacement therapy can reduce blood pressure in SCH patients, which needs to be validated in more clinical trials with larger samples.

Dual control of pituitary thyroid stimulating hormone secretion by thyroxine and triiodothyronine in athyreotic patients

BACKGROUND

Patient responses to levothyroxine (LT4) monotherapy vary considerably. We sought to differentiate contributions of FT4 and FT3 in controlling pituitary thyroid stimulating hormone (TSH) secretion.

METHODS

We retrospectively assessed the relationships between TSH and thyroid hormones in 319 patients with thyroid carcinoma through 2914 visits on various LT4 doses during follow-up for 5.5 years (median, IQR 4.2, 6.9). We also associated patient complaints with the relationships.

RESULTS

Under varying dose requirements (median 1.84 µg/kg, IQR 1.62, 2.11), patients reached TSH targets below 0.4, 0.1 or 0.01 mIU/l at 73%, 54% and 27% of visits. While intercept, slope and fit of linearity of the relationships between lnTSH and FT4/FT3 varied between individuals, gender, age, LT4 dose and deiodinase activity influenced the relationships in the cohort (all p < 0.001). Deiodinase activity impaired by LT4 dose significantly affected the lnTSH-FT4 relationship. Dose increase and reduced conversion efficiency displaced FT3-TSH equilibria. In LT4-treated patients, FT4 and FT3 contributed on average 52% versus 38%, and by interaction 10% towards TSH suppression. Symptomatic presentations (11%) accompanied reduced FT3 concentrations (-0.23 pmol/l, p = 0.001) adjusted for gender, age and BMI, their relationships being shifted towards higher TSH values at comparable FT3/FT4 levels.

CONCLUSIONS

Variation in deiodinase activity and resulting FT3 levels shape the TSH-FT4 relationship in LT4-treated athyreotic patients, suggesting cascade control of pituitary TSH production by the two hormones. Consequently, measurement of FT3 and calculation of conversion efficiency may identify patients with impaired biochemistry and a resulting lack of symptomatic control.

Recent Advances in Thyroid Hormone Regulation: Toward a New Paradigm for Optimal Diagnosis and Treatment

In thyroid health, the pituitary hormone thyroid-stimulating hormone (TSH) raises glandular thyroid hormone production to a physiological level and enhances formation and conversion of T4 to the biologically more active T3. Overstimulation is limited by negative feedback control. In equilibrium defining the euthyroid state, the relationship between TSH and FT4 expresses clusters of genetically determined, interlocked TSH-FT4 pairs, which invalidates their statistical correlation within the euthyroid range. Appropriate reactions to internal or external challenges are defined by unique solutions and homeostatic equilibria. Permissible variations in an individual are much more closely constrained than over a population. Current diagnostic definitions of subclinical thyroid dysfunction are laboratory based, and do not concur with treatment recommendations. An appropriate TSH level is a homeostatic concept that cannot be reduced to a fixed range consideration. The control mode may shift from feedback to tracking where TSH becomes positively, rather than inversely related with FT4. This is obvious in pituitary disease and severe non-thyroid illness, but extends to other prevalent conditions including aging, obesity, and levothyroxine (LT4) treatment. Treatment targets must both be individualized and respect altered equilibria on LT4. To avoid amalgamation bias, clinically meaningful stratification is required in epidemiological studies. In conclusion, pituitary TSH cannot be readily interpreted as a sensitive mirror image of thyroid function because the negative TSH-FT4 correlation is frequently broken, even inverted, by common conditions. The interrelationships between TSH and thyroid hormones and the interlocking elements of the control system are individual, dynamic, and adaptive. This demands a paradigm shift of its diagnostic use.

Poorly Controlled Congenital Hypothyroidism due to an Underlying Allgrove Syndrome

BACKGROUND

Congenital hypothyroidism of thyroidal origin (CHT) is a common disorder in pediatric endocrinology practices, which can be difficult to manage. Elevated thyrotropin (TSH) concentrations are in the great majority of cases explained by poor compliance to levothyroxine therapy.

METHODS

Case description.

RESULTS

We present a boy with CHT, with 2 heterozygous mutations in the TSH receptor gene, who showed persistently elevated TSH concentrations and psychomotor retardation, initially misinterpreted as malcompliance. At the age of 4 years, he was diagnosed with adrenal insufficiency, wherefore a broad diagnostic search was initiated. After the start of glucocorticoid replacement therapy, his TSH normalized and the levothyroxine could be lowered. At the age of 6 years, his TSH increased again, this time caused by malabsorption of levothyroxine due to esophageal achalasia. In retrospect, alacrima was also present and the diagnosis of Allgrove syndrome was genetically confirmed. The CHT was considered a separate disease entity.

CONCLUSIONS

In case of persistently elevated TSH levels in children with CHT, causes other than noncompliance must be considered. Second, in establishing the cause of adrenal insufficiency, specific symptoms, such as alacrima, are easily overlooked. Third, Allgrove syndrome is a rare disorder, in which diagnostic delay can lead to potentially life-threatening complications.

Effects of thyroxine replacement on endothelial function and carotid artery intima-media thickness in female patients with mild subclinical hypothyroidism

BACKGROUND

Previous studies have suggested an association between subclinical hypothyroidism and coronary artery disease that could be related to changes in serum lipids or endothelial dysfunction.

METHODS

Thirty-two female subclinical hypothyroidism patients were randomly assigned to 12 months of L-thyroxine replacement or no treatment. Endothelial function was measured by the flow-mediated vasodilatation of the brachial artery, as well as mean carotid artery intima-media thickness, and lipid profiles were studied at baseline and after 12 months of follow-up.

RESULTS

The mean ( ± SD) serum thyroid-stimulating hormone levels in the L-thyroxine replacement and control groups were 6.09 ± 1.32 and 6.27 ± 1.39 μUI/ml, respectively. No relationship between carotid artery intima-media thickness or brachial flow-mediated vasodilatation and free T4 and serum thyroid-stimulating hormone was found. The median L-T4 dose was 44.23 ± 18.13 μg/day. After 12 months, there was a significant decrease in the flow-mediated vasodilatation in the subclinical hypothyroidism control group (before: 17.33 ± 7.88 to after: 13.1 ± 4.75%, p =0.03), but there were no significant differences in flow-mediated vasodilatation in the L-thyroxine treated group (before: 16.81 ± 7.0 to after: 18.52 ± 7.44%, p = 0.39). We did not find any significant change in mean carotid intimamedia thickness after 12 months of L-thyroxine treatment.

CONCLUSION

Replacement therapy prevents a decline in flow-mediated vasodilatation with continuation of the subclinical hypothyroidism state. Large prospective multicenter placebo-controlled trials are necessary to investigate endothelial physiology further in subclinical hypothyroidism patients and to define the role of L-thyroxine therapy in improving endothelial function in these patients.