Thyroid function is more strongly associated with body impedance than anthropometry in healthy subjects

Myxedema in Both Hyperthyroidism and Hypothyroidism: A Hormetic Response?

Myxedema is a potentially life-threatening condition typically observed in severe hypothyroidism. However, localized or diffuse myxedema is also observed in hyperthyroidism. The exact cause and mechanism of this paradoxical situation is not clear. We report here the analysis of body fluid distribution by bioelectrical impedance analysis (BIA) in 103 thyroid patients, subdivided according to their functional status. All BIA parameters measured in subclinical thyroid dysfunctions did not significantly differ from those observed in euthyroid controls. On the contrary, they were clearly altered in the two extreme, opposite conditions of thyroid dysfunctions, namely overt hyperthyroidism and severe hypothyroidism, indicating the occurrence of a typical hormetic condition. Surprisingly, differences in BIA parameters related to fluid body composition were even more evident in hyperthyroidism than in hypothyroidism. A hormetic response to thyroid hormone (TH)s was previously reported to explain the paradoxical, biphasic, time- and dose-dependent effects on other conditions. Our results indicate that myxedema, observed in both hypothyroid and hyperthyroid conditions, represents another example of a hormetic-type response to THs. BIA offers no additional valuable information in evaluating fluid body composition in subclinical thyroid dysfunctions, but it represents a valuable method to analyze and monitor body fluid composition and distribution in overt and severe thyroid dysfunctions.

Nonthyroidal illness syndrome (NTIS) in severe COVID-19 patients: role of T3 on the Na/K pump gene expression and on hydroelectrolytic equilibrium

Background

Nonthyroidal Illness Syndrome (NTIS) can be detected in many critical illnesses. Recently, we demonstrated that this condition is frequently observed in COVID-19 patients too and it is correlated with the severity the disease. However, the exact mechanism through which thyroid hormones influence the course of COVID-19, as well as that of many other critical illnesses, is not clear yet and treatment with T4, T3 or a combination of both is still controversial. Aim of this study was to analyze body composition in COVID-19 patients in search of possible correlation with the thyroid function.

Methods and findings

We report here our experience performed in 74 critically ill COVID-19 patients hospitalized in the intensive care unit (ICU) of our University Hospital in Rome. In these patients, we evaluated the thyroid hormone function and body composition by Bioelectrical Impedance Analysis (BIA) during the acute phase of the disease at admission in the ICU. To examine the effects of thyroid function on BIA parameters we analyzed also 96 outpatients, affected by thyroid diseases in different functional conditions. We demonstrated that COVID-19 patients with low FT3 serum values exhibited increased values of the Total Body Water/Free Fat Mass (TBW/FFM) ratio. Patients with the lowest FT3 serum values had also the highest level of TBW/FFM ratio. This ratio is an indicator of the fraction of FFM as water and represents one of the best-known body-composition constants in mammals. We found an inverse correlation between FT3 serum values and this constant. Reduced FT3 serum values in COVID-19 patients were correlated with the increase in the total body water (TBW), the extracellular water (ECW) and the sodium/potassium exchangeable ratio (Na_e:K_e), and with the reduction of the intracellular water (ICW). No specific correlation was observed in thyroid patients at different functional conditions between any BIA parameters and FT3 serum values, except for the patient with myxedema, that showed a picture similar to that seen in COVID-19 patients with NTIS. Since the Na⁺/K⁺ pump is a well-known T3 target, we measured the mRNA expression levels of the two genes coding for the two major isoforms of this pump. We demonstrated that COVID-19 patients with NTIS had lower levels of mRNA of both genes in the peripheral blood mononuclear cells (PBMC)s obtained from our patients during the acute phase of the disease. In addition, we retrieved data from transcriptome analysis, performed on human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM)s treated with T3 and we demonstrated that in these cells T3 is able to stimulate the expression of these two genes in a dose-dependent manner.

Conclusions

In conclusion, we demonstrated that measurement of BIA parameters is a useful method to analyze water and salt retention in COVID-19 patients hospitalized in ICU and, in particular, in those that develop NTIS. Our results indicate that NTIS has peculiar similarities with myxedema seen in severe hypothyroid patients, albeit it occurs more rapidly. The Na⁺/K⁺ pump is a possible target of T3 action, involved in the pathogenesis of the anasarcatic condition observed in our COVID-19 patients with NTIS. Finally, measurement of BIA parameters may represent good endpoints to evaluate the benefit of future clinical interventional trials, based on the administration of T3 in patients with NTIS.

Effect of restoration of euthyroidism on visfatin concentrations and body composition in women

Dysregulation of thyroid function has known impact on body metabolism, however, data regarding metabolic outcome after restoration of thyroid function is limited. Therefore, the aim of the study was to investigate the effect of restoration of euthyroidism on serum visfatin, and its associations with insulin resistance and body composition. This is an observational study with consecutive enrollment. Forty-nine hyperthyroid (median age of 34 years) and 44 hypothyroid women (median age of 46 years) completed the study. Laboratory parameters and body composition analysis were assessed before and after the therapy. In the hyperthyroid group, visfatin concentrations increased (P < 0.0001), while glucose concentrations decreased (P < 0.0001). Total body mass and fat mass in the trunk and limbs significantly increased during the treatment. In the hypothyroid group, significant weight loss resulted from decrease of fat and muscle masses in trunk and limbs. Visfatin serum concentrations positively correlated with total fat mass (r = 0.19, P = 0.01) and insulin concentrations (r = 0.17, P = 0.018). In conclusion, restoration of thyroid function is not associated with beneficial changes in body composition, especially among hyperthyroid females.

Treatment with thyroid hormone

Thyroid hormone deficiency can have important repercussions. Treatment with thyroid hormone in replacement doses is essential in patients with hypothyroidism. In this review, we critically discuss the thyroid hormone formulations that are available and approaches to correct replacement therapy with thyroid hormone in primary and central hypothyroidism in different periods of life such as pregnancy, birth, infancy, childhood, and adolescence as well as in adult patients, the elderly, and in patients with comorbidities. Despite the frequent and long term use of l-T4, several studies have documented frequent under- and overtreatment during replacement therapy in hypothyroid patients. We assess the factors determining l-T4 requirements (sex, age, gender, menstrual status, body weight, and lean body mass), the major causes of failure to achieve optimal serum TSH levels in undertreated patients (poor patient compliance, timing of l-T4 administration, interferences with absorption, gastrointestinal diseases, and drugs), and the adverse consequences of unintentional TSH suppression in overtreated patients. Opinions differ regarding the treatment of mild thyroid hormone deficiency, and we examine the recent evidence favoring treatment of this condition. New data suggesting that combined therapy with T3 and T4 could be indicated in some patients with hypothyroidism are assessed, and the indications for TSH suppression with l-T4 in patients with euthyroid multinodular goiter and in those with differentiated thyroid cancer are reviewed. Lastly, we address the potential use of thyroid hormones or their analogs in obese patients and in severe cardiac diseases, dyslipidemia, and nonthyroidal illnesses.

Using body mass index to predict optimal thyroid dosing after thyroidectomy

BACKGROUND

Current postoperative thyroid replacement dosing is weight based, with adjustments made after thyroid-stimulating hormone values. This method can lead to considerable delays in achieving euthyroidism and often fails to accurately dose over- and underweight patients. Our aim was to develop an accurate dosing method that uses patient body mass index (BMI) data.

STUDY DESIGN

A retrospective review of a prospectively collected thyroid database was performed. We selected adult patients undergoing thyroidectomy, with benign pathology, who achieved euthyroidism on thyroid hormone supplementation. Body mass index and euthyroid dose were plotted and regression was used to fit curves to the data. Statistical analysis was performed using STATA 10.1 software (Stata Corp).

RESULTS

One hundred twenty-two patients met inclusion criteria. At initial follow-up, only 39 patients were euthyroid (32%). Fifty-three percent of patients with BMI >30 kg/m(2) were overdosed, and 46% of patients with BMI <25 kg/m(2) were underdosed. The line of best fit demonstrated an overall quadratic relationship between BMI and euthyroid dose. A linear relationship best described the data up to a BMI of 50. Beyond that, the line approached 1.1 μg/kg. A regression equation was derived for calculating initial levothyroxine dose (μg/kg/d = -0.018 × BMI + 2.13 [F statistic = 52.7, root mean square error of 0.24]).

CONCLUSIONS

The current standard of weight-based thyroid replacement fails to appropriately dose underweight and overweight patients. Body mass index can be used to more accurately dose thyroid hormone using a simple formula.

Relationship between serum TSH level with obesity and NAFLD in euthyroid subjects

To explore the relationship between serum thyroid stimulating hormone (TSH) level and obesity and nonalcoholic fatty liver disease (NAFLD) in euthyroid subjects, 1322 subjects were subjected to a questionnaire survey and physical examination. Fasting blood samples were collected to test serum TSH, plasma glucose and lipids. Fatty liver was diagnosed by type B ultrasonography. The relationship between serum TSH level and body mass index (BMI), percentage of body fat and NAFLD was analyzed. The results showed that serum TSH level was significantly higher in females than in males at the same group, and it was significantly higher in overweight group than in control group. Levels of body weight, BMI, waist circumference and percentage of body fat were increased in TSH >2.5 group compared to TSH ≤2.5 group in women. However, plasma lipids showed no significant differences. In males all the parameters showed no significant differences between two groups. Serum TSH was significantly correlated with body weight, BMI, waist circumference and percentage of body fat after adjustment for age in females. Multiple linear regression analysis revealed that percentage of body fat and BMI contributed significantly to the variance of TSH. Serum TSH level was significantly higher in nonalcoholic fatty liver group than in normal group in females. Multiple logistic regression analysis showed that TSH level was not the independent risk factor of NAFLD. Taken together the data suggest that serum TSH in normal range is significantly correlated with BMI and percentage of body fat in females. And the change of TSH level would not influence the prevalence of NAFLD.

Optimization of thyroxine replacement therapy after total or near-total thyroidectomy for benign thyroid disease

BACKGROUND

Total or near-total thyroidectomy is increasingly used to treat benign thyroid conditions. Lifelong treatment with thyroxine (T4) is then required, but the optimal dose is difficult to predict. This study investigated factors that might predict the ideal T4 dose, with the aim of reducing delays in achieving normal thyroid function after surgery.

METHODS

Data on 98 patients who underwent total or near-total thyroidectomy for benign disease were reviewed retrospectively. Patient and operative variables that might predict time to achieve normal thyroid function and optimal T4 replacement dose were examined. These data were then used to formulate an algorithm for T4 dosage, based on patient weight, that was subsequently applied prospectively to a comparable group of 27 patients.

RESULTS

The median time to achieve normal thyroid function was 14.5 (range 2-120) weeks before introduction of the algorithm, and was greater in patients needing large changes in T4 dose. In multivariate analysis, the best predictors of optimal T4 dose were bodyweight (r = 0.46, P < 0.001) and age (r = -0.32, P = 0.002). Subsequent use of a weight-related algorithm improved time to achieve normal thyroid function.

CONCLUSION

The T4 replacement dosage after total or near-total thyroidectomy is largely influenced by bodyweight. Use of a weight-related algorithm improves patient care compared with use of standard T4 dose-titration methods.