Non-thyroidal illness syndrome and SARS-CoV-2-associated multisystem inflammatory syndrome in children

Thyroiditis and COVID-19: focus on pediatric age. A narrative review

PURPOSE

In light of the growing concern over the possible link between SARS-CoV2 infection and autoimmune diseases, we conducted a review to investigate the impact of the pandemic outbreak on thyroid diseases.

METHODS

We carried out a narrative review of all pediatric cases described in the literature, mainly focusing on the possible association of COVID-19 with the incidence of autoimmune and post-infective thyroid diseases (namely Hashimoto's Thyroiditis (HT), Grave's Disease (GD) and Sub-Acute Thyroiditis (SAT)). We also felt it was necessary to provide a brief review of Non-thyroidal Illness Syndrome (NTIS) and Multisystem Inflammatory Syndrome in Children (MIS-C) because of their overlap with thyroiditis.

RESULTS

There is currently no conclusive evidence linking SARS-CoV-2 infection with an increased incidence of autoimmune thyroiditis (AT) in pediatric age. However, SAT may be a mild complication of SARS-CoV-2 infection, as is the case with other viral infections. SAT typically resolves on its own and does not require treatment. NTIS may be associated with inflammatory complications, such as MIS-C, and admission to intensive care. It may also be considered a prognostic risk factor for severe disease. The hypothesized pathogenetic mechanisms of thyroid damage in COVID-19 include direct damage due to the significant expression of angiotensin-converting enzyme 2 (ACE2) in the thyroid gland, which is a ligand for the virus, and indirect damage due to immune dysregulation, such as the overproduction of IL-6, which is thought to be part of the pathogenesis of thyroiditis.

CONCLUSION

However, due to the limited evidence available, further prospective longitudinal studies are required to clarify the relationship between COVID-19 and thyroid disease in children and adolescents, as well as to investigate any potential long-term consequences.

The prognostic significance of insulin resistance in COVID-19: a review

Objectives

Emerging publications indicate that diabetes predisposes patients with COVID-19 to more severe complications, which is partly attributed to inflammatory condition. In the current review, we reviewed recent published literature to provide evidence on the role of insulin resistance (IR) in diabetes, the association between diabetes and COVID-19 severity and mortality, the impact of COVID-19 infection on incident new-onset diabetes, mechanisms responsible for IR in COVID-19 patients, and the predictive value of different surrogates of IR in COVID-19.

Method

The literature search performs to find out studies that have assessed the association between IR surrogates and morbidity and mortality in patients with COVID-19.

Results

We showed that there is a bulk of evidence in support of the fact that diabetes is a potent risk factor for enhanced morbidity and mortality in COVID-19 patients. COVID-19 patients with diabetes are more prone to remarkable dysglycemia compared to those without diabetes, which is associated with an unfavourable prognosis. Furthermore, SARS-COV2 can make patients predispose to IR and diabetes via activating ISR, affecting RAAS signaling pathway, provoking inflammation, and changing the expression of PPARɣ and SREBP-1. Additionally, higher IR is associated with increased morbidity and mortality in COVID-19 patients and different surrogates of IR can be utilized as a prognostic biomarker for COVID-19 patients.

Conclusion

Different surrogates of IR can be utilized as predictors of COVID-19 complications and death.

The use of triiodothyronine during critical illness

PURPOSE OF REVIEW

Thyroid hormone physiology changes during critical illness. Circulating concentration of triiodothyronine (T3), the active form of thyroid hormone decreases. It has long been uncertain whether this represents a pathologic change or if it is an adaptive phenomenon. Controlled clinical trials have been required to understand whether replacing and restoring serum T3 levels is therapeutic.

RECENT FINDINGS

Clinical trials of T3 have recently been proposed with some completed. These have been conducted in patients with sepsis, myocardial infarction, infants undergoing cardiac surgery, and acute respiratory distress syndrome. Of the completed trials, T3 administration restored serum concentrations, but was not accompanied by significant clinical benefit. Importantly, restoring serum T3 levels did not cause any adverse effects.

SUMMARY

If T3 is to be considered a therapeutic target in critical illness, further studies should consider the stage of disease it is administered, and whether there are other surrogate measures to assess adequacy of hormone replacement over and above serum T3 concentrations.

The Interplay Between COVID-19 and Pediatric Endocrine Disorders. What have we Learned After More than Three Years of the Pandemic?

As an increased body of COVID-19 related research is now available, it becomes apparent that the effects of COVID-19 extend beyond that of the respiratory system. Among others, the endocrine system is particularly vulnerable to perturbation from the COVID-19 infection. The present scoping review summarizes the bidirectional relationship between COVID-19 and endocrine system in children and adolescents, by describing both the possible susceptibility of children and adolescents without endocrinopathies to endocrine disorders following COVID-19 infection, but also the potential susceptibility to COVID-19 infection and severe infection, or the aggravation of endocrine dysfunction in patients with pre-existing endocrine diseases. Data suggest increased obesity and diabetes rates, as well as increased severity and frequency of diabetic ketoacidosis following COVID-19 infection. Conversely, patients with diabetes and obesity may experience a more severe course of COVID-19 infection. However, in the majority of cases, children and adolescents with well-managed and regulated endocrine disorders do not appear to be at increased risk of infection or severe infection from COVID-19. Thus, adhering to the appropriate "sick day management rules", maintaining adequate supply of medications and supplies, keeping close contact with the therapeutic team and seeking medical help without delay when needed, are the main recommendations for a safe outcome. Additional lessons learnt during the pandemic include the risk for mental health diseases caused by children's disrupted routine due to COVID-19 related protective measures and the importance of adopting alternative communication options, such as telehealth visits, in order to ensure uninterrupted endocrine care.

Cell-free DNA reveals distinct pathology of multisystem inflammatory syndrome in children

Multisystem inflammatory syndrome in children (MIS-C) is a rare but life-threatening hyperinflammatory condition induced by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes pediatric COVID-19 (pCOVID-19). The relationship of the systemic tissue injury to the pathophysiology of MIS-C is poorly defined. We leveraged the high sensitivity of epigenomics analyses of plasma cell-free DNA (cfDNA) and plasma cytokine measurements to identify the spectrum of tissue injury and glean mechanistic insights. Compared with pediatric healthy controls (pHCs) and patients with pCOVID-19, patients with MIS-C had higher levels of cfDNA primarily derived from innate immune cells, megakaryocyte-erythroid precursor cells, and nonhematopoietic tissues such as hepatocytes, cardiac myocytes, and kidney cells. Nonhematopoietic tissue cfDNA levels demonstrated significant interindividual variability, consistent with the heterogenous clinical presentation of MIS-C. In contrast, adaptive immune cell-derived cfDNA levels were comparable in MIS-C and pCOVID-19 patients. Indeed, the cfDNA of innate immune cells in patients with MIS-C correlated with the levels of innate immune inflammatory cytokines and nonhematopoietic tissue-derived cfDNA, suggesting a primarily innate immunity-mediated response to account for the multisystem pathology. These data provide insight into the pathogenesis of MIS-C and support the value of cfDNA as a sensitive biomarker to map tissue injury in MIS-C and likely other multiorgan inflammatory conditions.

Endocrinological Involvement in Children and Adolescents Affected by COVID-19: A Narrative Review

Since the advent of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, an increased incidence of several endocrinological anomalies in acute-phase and/or long-term complications has been described. The aim of this review is to provide a broad overview of the available literature regarding changes in the worldwide epidemiology of endocrinological involvement in children since December 2019 and to report the evidence supporting its association with coronavirus disease 2019 (COVID-19). Although little is known regarding the involvement of endocrine organs during COVID-19 in children, the current evidence in adults and epidemiological studies on the pediatric population suggest the presence of a causal association between the virus and endocrinopathies. Untreated transient thyroid dysfunction, sick euthyroid syndrome, nonthyroidal illness syndrome, and hypothalamic-pituitary-adrenal (HPA) axis and central precocious puberty have been observed in children in acute infection and/or during multisystem inflammatory syndrome development. Furthermore, a higher frequency of ketoacidosis at onset in children with a new diagnosis of type 1 diabetes is reported in the literature. Although the direct association between COVID-19 and endocrinological involvement has not been confirmed yet, data on the development of different endocrinopathies in children, both during acute infection and as a result of its long-term complications, have been reported. This information is of primary importance to guide the management of patients with previous or current COVID-19.

Prognostic role of euthyroid sick syndrome in MIS-C: results from a single-center observational study

Background

Euthyroid sick syndrome (ESS) is characterized by low serum levels of free triiodothyronine (fT3) with normal or low levels of thyroid stimulating hormone (TSH) and free thyroxine (fT4) and is reported in different acute clinical situations, such as sepsis, diabetic ketoacidosis and after cardiac surgery. Our aim was to evaluate the predicting role of ESS for disease severity in patients with Multisystem Inflammatory Syndrome in children (MIS-C).

Methods

A single-centre observational study on consecutive patients with MIS-C. Before treatment clinical, and laboratory data were collected and, in a subset of patients, thyroid function tests were repeated 4 weeks later. Variables distribution was analyzed by Mann-Whitney U-test and correlations between different parameters were calculated by Spearman's Rho coefficient.

Results

Forty-two patients were included and 36 (85.7%) presented ESS. fT3 values were significantly lower in patients requiring intensive care, a strong direct correlation was shown between fT3 and Hb, platelet count and ejection fraction values. A significant inverse correlation was retrieved between fT3 levels and C-reactive protein, brain natriuretic peptide, IL-2 soluble receptor and S-100 protein. Subjects with severe myocardial depression (EF < 45%) had lower fT3 values than subjects with higher EF. The thyroid function tests spontaneously normalized in all subjects who repeated measurement 4 weeks after admission.

Conclusion

ESS is a frequent and transient condition in acute phase of MIS-C. A severe reduction of fT3 must be considered as important prognostic factor for severe disease course, with subsequent relevant clinical impact in the management of these patients.

Endocrine manifestations of COVID-19 in children: A scoping review

In this review, we explore associations between SARS CoV-2 infection and the endocrine system and metabolism in children and adolescents. PubMed, Scopus and Google scholar databases were searched to identify published data on endocrine manifestations of COVID-19 in children up to 31 March 2023, including diabetes, obesity, puberty, thyroid disorders, adrenal disorders and pituitary disorders. Data on changes in disease pattern/ incidence, disease control, and other effects due to the COVID-19 pandemic, as well as effects of pre-existing endocrine conditions on severity of COVID-19 infection are presented, and practice points and research needs provided under each section.

The triglyceride-glucose index as an indicator of insulin resistance and cardiometabolic risk in Brazilian adolescents

Objective

To set cutoff points for the triglyceride and glucose index (TyG) as a marker of insulin resistance (IR) for the pediatric population.

Subjects and methods

This was a cross-sectional study with schoolchildren population-based data using data of 377 schoolchildren age 10 to 17 years of both sexes. We studied metabolic variables associated with IR indicators, such as fasting insulin and blood glucose, to calculate the homeostatic model assessment (HOMA-IR), and we studied triglycerides (TG) to determine the TyG index. We obtained TyG cutoff values for IR using the receiver operation characteristic (ROC), with definitions of sensitivity (Sen), specificity (Spe), and area under the ROC curve (AUC), with the HOMA-IR as reference.

Results

The cutoff points of the TyG index for IR in adolescents are 7.94 for both sexes, 7.91 for boys, and 7.94 for girls, indicating moderate discriminatory power. When we also considered anthropometric variables of excess weight [TyG-BMI (body mass index)] and visceral fat [TyG-WC (waist circumference)], these indexes reached AUC values higher than 0.72, enhancing their potential use for a good diagnosis.

Conclusion

TyG has proven to be a useful instrument for identifying IR in adolescent health screening, with high discrimination capacity when added to anthropometric variables, making it a feasible and inexpensive option.

Changes in thyroid function in children with multisystem inflammatory syndrome related to COVID-19 observed over a 1-year follow-up period

not required.

A Literature Review on SARS-CoV-2 and Other Viruses in Thyroid Disorders: Environmental Triggers or No-Guilty Bystanders?

A growing number of findings indicate a relationship between COVID-19 infection and thyroid dysfunction. This association is also strengthened by knowledge on the potential of viral infections to trigger thyroid disorders, although the exact underlying pathogenetic process remains to be elucidated. This review aimed to describe the available data regarding the possible role of infectious agents, and in particular of SARS-CoV-2, in the development of thyroid disorders, summarizing the proposed mechanisms and levels of evidence (epidemiological, serological or direct presence of the viruses in the thyroid gland) by which the infection could be responsible for thyroid abnormalities/diseases. Novel data on the association and mechanisms involved between SARS-CoV-2 vaccines and thyroid diseases are also discussed. While demonstrating a clear causal link is challenging, numerous clues at molecular and cellular levels and the large amount of epidemiological data suggest the existence of this relationship. Further studies should be taken to further investigate the true nature and strength of this association, to help in planning future preventive and therapeutic strategies for more personal and targeted care with attention to the underlying causes of thyroid dysfunction.

Are Thyroid Functions Affected in Multisystem Inflammatory Syndrome in Children?

OBJECTIVE

Multisystem inflammatory syndrome in children (MIS-C), associated with Coronavirus disease-2019, is defined as the presence of documented fever, inflammation, and at least two signs of multisystem involvement and lack of an alternative microbial diagnosis in children who have recent or current Severe acute respiratory syndrome-Coronavirus-2 infection or exposure. In this study, we evaluated thyroid function tests in pediatric cases with MIS-C in order to understand how the hypothalamus-pituitary-thyroid axis was affected and to examine the relationship between disease severity and thyroid function.

METHODS

This case-control study was conducted between January 2021 and September 2021. The patient group consisted of 36 MIS-C cases, the control group included 72 healthy children. Demographic features, clinical findings, inflammatory markers, thyroid function tests, and thyroid antibody levels in cases of MIS-C were recorded. Thyroid function tests were recorded in the healthy control group.

RESULTS

When MIS-C and healthy control groups were compared, free triiodothyronine (fT3) level was lower in MIS-C cases, while free thyroxine (fT4) level was found to be lower in the healthy group (p<0.001, p=0.001, respectively). Although the fT4 level was significantly lower in controls, no significant difference was found compared with the age-appropriate reference intervals (p=0.318). When MIS-C cases were stratified by intensive care requirement, fT3 levels were also lower in those admitted to intensive care and also in those who received steroid treatment (p=0.043, p<0.001, respectively).

CONCLUSION

Since the endocrine system critically coordinates and regulates important metabolic and biochemical pathways, investigation of endocrine function in MIS-C may be beneficial. These results show an association between low fT3 levels and both diagnosis of MIS-C and requirement for intensive care. Further studies are needed to predict the prognosis and develop a long-term follow-up management plan.

Treatment of hypothyroidism in infants, children and adolescents

In 2014, treatment guidelines from the American Thyroid Association reflected the general consensus that levothyroxine (LT4), adjusted to maintain a normal thyrotropin (TSH) level, is the preferred method for treatment of hypothyroidism. Although this is generally applicable to children, there are subsets of children for whom the diagnosis and treatment of hypothyroidism are problematic. These include children with congenital hypothyroidism (CH), low birth weight (LBW) and very low birth weight (VLBW), Down syndrome (DS), subclinical hypothyroidism, and obesity. In this Review, we focus on the progress and remaining pitfalls in diagnosis and treatment of hypothyroidism in these and other groups.

Multisystem Inflammatory Syndrome in Children Associated with COVID-19 Infection: A Comprehensive Review

The Multisystem Inflammatory Syndrome in Children (MIS-C) is a postinfectious syndrome associated with coronavirus disease 2019 (COVID-19) disease in children. The aim of this study is to conduct a thorough review to assist health care professionals in diagnosis and management of this complication of COVID-19 disease in children. A thorough systematic review was conducted through an on-line search based on MIS-C with the primary focus on epidemiology, clinical characteristics, diagnosis, pathophysiology, management, and long-term follow-up. This syndrome is characterized by an exaggerated and uncontrolled release of proinflammatory cytokines involving dysfunction of both innate and adaptive immunity. In this review, a summary of observational studies and case reports was conducted, in which we found that MIS-C generates multiple-organ failure frequently presenting with hemodynamic instability further characterized by Kawasaki-like symptoms (such as persistent high fever, polymorphic rash, and bilateral conjunctivitis) and predominance of gastrointestinal and cardiovascular signs and symptoms. Keys to effective management involve early diagnosis, timely treatment and re-evaluation following hospital discharge. Diagnosis is marked by significant elevation of inflammatory biomarkers, laboratory evidence of COVID-19 infection or history of recent exposure, and absence of any other plausible explanation for the associated signs, symptoms, and presentation. Management includes hemodynamic stabilization, empiric antibiotic therapy (de-escalation if cultures and polymerase chain reaction studies indicate no bacterial co-infection), immunomodulatory therapy (methylprednisolone, intravenous immunoglobulin, anakinra, tocilizumab, siltuximab, Janus kinase inhibitors, tumor necrosis factor-α inhibitors), antivirals (remdesivir), and anticoagulation (acetylsalicylic acid, unfractionated or low-molecular-weight heparin or new oral anticoagulants). In addition, we identified poor prognostic risk factors to include concurrent comorbidities, blood-component consumption and marrow suppression (lymphopenia, thrombocytopenia), depletion of homeostatic components (hypoalbuminemia), and marked evidence of a hyperinflammatory response to include elevated values of ferritin, C-reactive protein, and D-dimer. MIS-C constitutes a postinfectious syndrome characterized by a marked cytokine storm, characterized by fever, bilateral conjunctivitis, and multiple organ dysfunction. Promoting future research and long-term follow-up will be essential for the development of guidelines and recommendations leading to effective identification and management of MIS-C.

Thyroid-Stimulating Hormone Predicts Total Cholesterol and Low-Density Lipoprotein Cholesterol Reduction during the Acute Phase of COVID-19

A complex dysregulation of lipid metabolism occurs in COVID-19, leading to reduced total cholesterol (TC), LDL-cholesterol (LDL-C), and HDL-cholesterol (HDL-C) levels, along with a derangement of thyroid function, leading to reduced thyroid-stimulating hormone (TSH) levels. This study aimed to explore the association between TSH levels during COVID-19 and the variation (Δ) of lipid profile parameters in the period preceding (from 1 month up to 1 year) hospital admission due to COVID-19. Clinical data of 324 patients (mean age 76 ± 15 years, 54% males) hospitalized due to COVID-19 between March 2020 and March 2022 were retrospectively analyzed. The association between TSH levels at hospital admission and either Δ-TC, Δ-LDL-C, or Δ-HDL-C over the selected time frame was assessed through univariable and multivariable analyses. TSH levels were below the lower reference limit of 0.340 μUI/mL in 14% of COVID-19 patients. A significant reduction of plasma TC, LDL-C, and HDL-C was recorded between the two time points (p < 0.001 for all the comparisons). TSH was directly associated with Δ-TC (rho = 0.193, p = 0.001), Δ-LDL-C (rho = 0.201, p = 0.001), and Δ-HDL-C (rho = 0.160, p = 0.008), and inversely associated with C-reactive protein (CRP) (rho = −0.175, p = 0.004). Moreover, TSH decreased with increasing COVID-19 severity (p < 0.001). CRP and COVID-19 severity were inversely associated with Δ-TC, Δ-LDL-C, and Δ-HDL-C (p < 0.05 for all associations). A significant independent association was found between TSH and either Δ-TC (β = 0.125, p = 0.044) or Δ-LDL-C (β = 0.131, p = 0.036) after adjusting for multiple confounders including CRP and COVID-19 severity. In conclusion, lower levels of TSH may contribute to explain TC and LDL-C reduction in the acute phase of COVID-19.

Thyroid diseases are associated with coronavirus disease 2019 infection

BACKGROUND

In 2019, there was a global outbreak of new coronary pneumonia. Studies have found that the severity of patients with new coronary pneumonia may be related to their comorbidities. This article discusses the impact of thyroid disease on the severity of new coronary pneumonia through a meta-analysis and provides new treatment ideas for the later treatment and recovery of new coronary pneumonia.

METHODS

Databases including PubMed, Embase, Cochrane Library, SINOMED, China national knowledge infrastructure (CNKI), and Wanfang for coronavirus disease 2019 (COVID-19) infection and thyroid diseases were searched. Reference lists of all eligible articles and related previous review articles were handsearched. Fifty-three articles were included to conduct the meta-analysis.

RESULTS

Fifty-three articles with 12,022 COVID-19 infection patients were included in this meta-analysis. The proportion of patients with thyroid diseases in all COVID-19 infection patients fluctuates between 0% and 88.46%. Of the 53 included studies, 22 studies reported the severity of COVID-19 infection and grouped. The fixed-effects model was used to merge odds ratio (OR) values, and the pooled effect size in favor of non-severe patients is 2.62 (95% CI = 1.96-3.49, P < 0.0001), which means that patients with severe COVID-19 infection are more likely to have thyroid diseases. The analysis subgrouped into Asia and Europe shows that patients with COVID-19 severe infection in Asia are 3.77 times more likely to have thyroid diseases than non-severe patients (fixed-effects model: OR = 3.77, 95% CI = 2.66-5.35, P < 0.00001). No significant statistical heterogeneity was found by the heterogeneity analysis (chi-square = 19.85, P = 0.34, I ² = 9%). Severe COVID-19 infection patients are more likely to be complicated by hypothyroidism and low T3 syndrome. The pooled ORs with fixed-effects model are 3.72 (95% CI = 1.62-8.58, P = 0.002) and 5.86 (95% CI = 2.79-12.33, P < 0.00001), respectively.

CONCLUSION

COVID-19 infection patients with thyroid diseases are very common, and severe patients are more likely to have thyroid diseases. Asian COVID-19 infection, hypothyroidism patients, and patients with low T3 syndrome are more likely to progress to severe condition.

SYSTEMATIC REVIEW REGISTRATION

https://inplasy.com, identifier INPLASY202190079.

Six-month multidisciplinary follow-up in multisystem inflammatory syndrome in children: An Italian single-center experience

BACKGROUND

A severe multisystem inflammatory syndrome in children (MIS-C) related to SARS-CoV-2 has been described after infection. A limited number of reports have analyzed the long-term complications related to pro-inflammatory status in MIS-C. We evaluated multiorgan impairment at the 6-month follow-up in MIS-C.

METHODS

We enrolled 33 pediatric patients consecutively hospitalized for MIS-C and monitored for almost 6 months. The inter-relationship of patient's features and disease severity at admission with long term complications was studied by multivariate analysis.

RESULTS

Endo-metabolic derangement, cardiac injury, respiratory, renal and gastrointestinal manifestations and neurological involvement are part of the initial presentation. The most abnormalities appear to resolve within the first few weeks, without significant long term dysfunction at the 6-months follow-up, except for endocrine (non-thyroidal illness syndrome in 12.1%, insulin resistance in 21.2%) and neurological system (27.3% cognitive or psychological, behavioral, adaptive difficulties). Endocrine and heart involvement at admission represent a significant factor on the long term sequelae; however no association between severity score and long-term outcome was noted.

CONCLUSIONS

The severity of initial clinical presentation may be associated to organ domain, however it is not related to long term sequelae. The prevalent organ restoration supports a predominant indirect immune-mediated injury triggered by a systemic inflammatory response; however a direct damage due to the viral entry could be not excluded. Eventhought our preliminary results seem to suggest that MIS-C is not a long-term risk condition for children health, a longer follow-up is mandatory to confirm this hypothesis.

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.