Effects of either LT4 monotherapy or LT4/LT3 combined therapy in patients totally thyroidectomized for thyroid cancer

Combined T4 + T3 therapy versus T4 monotherapy effect on psychological health in hypothyroidism: A systematic review and meta-analysis

PURPOSE

To evaluate whether T4 + T3 combination therapy had advantages in improving psychological health compared with T4 monotherapy.

METHODS

We searched PubMed, Embase, Cochrane Library, and Web of Science from January 2000 to March 2021, and updated in September 2021. The inclusion criteria (prospective study, published in English, had a T4 + T3 combination therapy test group and a T4 monotherapy control group, patients aged ≥18 years and with overt primary hypothyroidism, and published after January 2000) were applied by two reviewers; any disagreement was resolved by a third reviewer. The two reviewers independently extracted data using a standard data form and assessed the risk of bias using the Cochrane risk of bias tool. Coprimary outcomes included the psychological health measures of depression, fatigue, pain, anxiety and anger, measured using validated and reliable instruments.

RESULTS

Eighteen of 2029 studies (883 patients) were included in the meta-analysis. No significant difference was found between T4 + T3 combination therapy and T4 monotherapy with regard to depression (standardized mean difference [SMD]: -0.06, 95% confidence interval [CI]: -0.18; 0.07), fatigue (SMD: 0.06, 95% CI: -0.13; 0.26), pain (SMD: -0.01, 95% CI: -0.24; 0.22), anxiety (SMD: 0.01, 95% CI: -0.15; 0.17) and anger (SMD: 0.05, 95% CI: -0.15; 0.24). Methodological heterogeneity had no influence on the results. The patients preferred combination therapy significantly.

CONCLUSIONS

Compared with T4 monotherapy, T4 + T3 combination therapy had no significant advantage in improving psychological health. For patients who are unsatisfied with LT4 monotherapy, the patient and the physician should make a joint decision concerning therapy.

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.

Levothyroxine Treatment and the Risk of Cardiac Arrhythmias - Focus on the Patient Submitted to Thyroid Surgery

Levothyroxine (LT4) is used to treat frequently encountered endocrinopathies such as thyroid diseases. It is regularly used in clinical (overt) hypothyroidism cases and subclinical (latent) hypothyroidism cases in the last decade. Suppressive LT4 therapy is also part of the medical regimen used to manage thyroid malignancies after a thyroidectomy. LT4 treatment possesses dual effects: substituting new-onset thyroid hormone deficiency and suppressing the local and distant malignancy spreading in cancer. It is the practice to administer LT4 in less-than-high suppressive doses for growth control of thyroid nodules and goiter, even in patients with preserved thyroid function. Despite its approved safety for clinical use, LT4 can sometimes induce side-effects, more often recorded with patients under treatment with LT4 suppressive doses than in unintentionally LT4-overdosed patients. Cardiac arrhythmias and the deterioration of osteoporosis are the most frequently documented side-effects of LT4 therapy. It also lowers the threshold for the onset or aggravation of cardiac arrhythmias for patients with pre-existing heart diseases. To improve the quality of life in LT4-substituted patients, clinicians often prescribe higher doses of LT4 to reach low normal TSH levels to achieve cellular euthyroidism. In such circumstances, the risk of cardiac arrhythmias, particularly atrial fibrillation, increases, and the combined use of LT4 and triiodothyronine further complicates such risk. This review summarizes the relevant available data related to LT4 suppressive treatment and the associated risk of cardiac arrhythmia.

Liothyronine and Desiccated Thyroid Extract in the Treatment of Hypothyroidism

Background: The basis for the treatment of hypothyroidism with levothyroxine (LT4) is that humans activate T4 to triiodothyronine (T3). Thus, while normalizing serum thyrotropin (TSH), LT4 doses should also restore the body's reservoir of T3. However, there is evidence that T3 is not fully restored in LT4-treated patients. Summary: For patients who remain symptomatic on LT4 therapy, clinical guidelines recommend, on a trial basis, therapy with LT4+LT3. Reducing the LT4 dose by 25 mcg/day and adding 2.5-7.5 mcg liothyronine (LT3) once or twice a day is an appropriate starting point. Transient episodes of hypertriiodothyroninemia with these doses of LT4 and LT3 are unlikely to go above the reference range and have not been associated with adverse drug reactions. Trials following almost a 1000 patients for almost 1 year indicate that similar to LT4, therapy with LT4+LT3 can restore euthyroidism while maintaining a normal serum TSH. An observational study of 400 patients with a mean follow-up of ∼9 years did not indicate increased mortality or morbidity risk due to cardiovascular disease, atrial fibrillation, or fractures after adjusting for age when compared with patients taking only LT4. Desiccated thyroid extract (DTE) is a form of combination therapy in which the LT4/LT3 ratio is ∼4:1; the mean daily dose of DTE needed to normalize serum TSH contains ∼11 mcg T3, but some patients may require higher doses. The DTE remains outside formal FDA oversight, and consistency of T4 and T3 contents is monitored by the manufacturers only. Conclusions: Newly diagnosed hypothyroid patients should be treated with LT4. A trial of combination therapy with LT4+LT3 can be considered for those patients who have unambiguously not benefited from LT4.

Biochemical bone turnover markers in hormonal disorders in adults: a narrative review

BACKGROUND

Hormonal disorders are often associated with abnormal levels of bone turnover markers (BTMs). N-terminal propeptide of type I procollagen (PINP) and serum C-terminal cross-linking telopeptide of type I collagen (CTX-I) are the reference markers of bone formation and bone resorption, respectively.

METHODS

A comprehensive literature search within the MEDLINE and Web of Science databases was performed.

RESULTS

Acromegaly is associated with higher BTM levels, which decrease during the remission after treatment. Adult-onset growth hormone deficiency is often associated with decreased BTM levels. Growth hormone replacement therapy stimulates bone turnover and increases BTM levels. Hypothyroidism is characterized by general slowing of bone metabolism which is reflected by lower BTM levels. The replacement thyroid hormone therapy increases the bone turnover rate and BTM levels increase. Patients with thyroid cancer receive a suppressive dose of thyroid hormones and may have slightly elevated BTM levels. Patients with overt hyperthyroidism had higher BTM levels and anti-thyroid therapy induces a rapid decrease in the BTM levels. Patients with overt primary hyperparathyroidism have higher BTM levels, whereas those with asymptomatic and normocalcemic hyperparathyroidism usually have normal BTM levels. Hypoparathyroidism is characterized by slightly decreased BTM levels. Cushing's syndrome is characterized consistently by markedly decreased osteocalcin concentration, whereas data on other BTMs are discordant.

CONCLUSIONS

BTMs help us to better understand mechanisms of the impact of hormonal disorders and their treatment on bone metabolism. However, it is unknown whether BTMs may be used to monitor the effect of their treatments on bone in the clinical practice.

Effects of Long-Term Combination LT4 and LT3 Therapy for Improving Hypothyroidism and Overall Quality of Life

Guidelines from the American Thyroid Association and the American Association of Clinical Endocrinologists suggest monitoring thyroid-stimulating hormone and serum-free thyroxine to make clinical decisions for starting and monitoring therapy with their mainstay treatment of levothyroxine monotherapy. Although this monotherapy provides adequate control of symptoms for the majority of the population, a strong subset of the population continues to complain of hypothyroidism despite normal thyroid-stimulating hormone and serum-free thyroxine levels. Combination levothyroxine and liothyronine therapy to improve symptoms of hypothyroidism has been a topic of interest for several decades, but the data have been mixed. This study provides insight into the effects of combination therapy because there is no reported retrospective or prospective study in the literature.

Supplemental digital content is available in the text.

Objectives

Hypothyroidism results in decreased mood and neurocognition, weight gain, fatigue, and many other undesirable symptoms. The American Association of Clinical Endocrinologists, the American Thyroid Association (ATA), and The Endocrine Society recommend levothyroxine (LT4) monotherapy as the treatment for hypothyroidism; however, after years of monotherapy, some patients continue to experience impaired quality of life. Combination LT4 and synthetic liothyronine (LT3) therapy or the use of desiccated thyroid extract (DTE), has not been suggested for this indication based on short-duration studies with no significant benefits. Our first observational study examined the role of combination therapy for 6 years in improving quality of life in a subset of a hypothyroid population without adverse effects and cardiac mortality.

Methods

An observational retrospective study examining patients prescribed thyroid replacements with serum triiodothyronine (FT3), LT4 with LT3 (synthetic therapy) or DTE (natural therapy), compared with LT4 alone in the United States from 2010 to 2016. Thyroid-stimulating hormone (TSH), serum thyroxine (FT4), and FT3 levels were documented for each patient in addition to any admissions of myxedema coma, thyrotoxicosis, or cardiovascular complications, such as arrhythmias, atrial fibrillation, and mortality. At the conclusion of the study, a cross-sectional interview assessed quality of life for each combination therapy through the Medical Outcomes Study Short Form-20 questionnaire.

Results

Compared with patients taking only LT4, 89.47% using synthetic therapy had therapeutic TSH (P < 0.05). Similarly, 96.49% using natural therapy had therapeutic TSH (P < 0.05). Less than 5% of patients had supratherapeutic FT3. None of the patients who had abnormally low TSH or elevated FT3 or FT4 levels had hospitalizations for arrhythmias or thyrotoxicosis. On the Medical Outcomes Study Short Form-20 questionnaire, >92% answered feeling “excellent, very good, or good” when questioned about their health while undergoing thyroid replacement compared with levothyroxine alone.

Conclusions

This is the only retrospective study reported to use long-term (mean 27 months) thyroid replacements with combination therapy and to compare between the two forms of therapy: synthetic and natural. For patients undergoing either therapy, we did not identify additional risks of atrial fibrillation, cardiovascular disease, or mortality in patients of all ages with hypothyroidism.

Treatment of hypothyroidism with levothyroxine plus liothyronine: a randomized, double-blind, crossover study

OBJECTIVE

To compare the effects of a unique fixed combination levothyroxine/liothyronine (LT4/LT3) therapy in patients with primary hypothyroidism.

SUBJECTS AND METHODS

This is a randomized, double-blind, crossover study. Adults with primary hypothyroidism (n = 32, age 42.6 ± 13.3, 30 females) on stable doses of LT4 for ≥ 6 months (125 or 150 μg/day) were randomized to continue LT4 treatment (G1) or to start LT4/LT3 therapy (75/15 μg/day; G2). After 8 weeks, participants switched treatments for 8 more weeks. Thyroid function, lipid profile, plasma glucose, body weight, electrocardiogram, vital signs, and quality of life (QoL) were evaluated at weeks 0, 8 and 16.

RESULTS

Free T4 levels were significantly lower while on LT4/LT3 (G1: 1.07 ± 0.29 vs. 1.65 ± 0.46; G2: 0.97 ± 0.26 vs. 1.63 ± 0.43 ng/dL; P < 0.001). TSH and T3 levels were not affected by type of therapy. More patients on LT4/LT3 had T3 levels above the upper limit (15% vs. 3%). The combination therapy led to an increase in heart rate, with no significant changes in electrocardiogram or arterial blood pressure. Lipid profile, body weight and QoL remained unchanged.

CONCLUSIONS

The combination therapy yielded significantly lower free T4 levels, with no changes in TSH or T3 levels. More patients on LT4/T3 had elevated T3 levels, with no significant alterations in the evaluated outcomes. No clear clinical benefit of the studied formulation could be observed. Future trials need to evaluate different formulations and the impact of the combined therapy in select populations with genetic polymorphisms.

Individually-tailored thyroxine requirement in the same patients before and after thyroidectomy: a longitudinal study

OBJECTIVE

Thyroxine (T4) requirement after total thyroidectomy for differentiated thyroid carcinoma (DTC) is a debated issue. As most of the studies in the area have been retrospective and/or performed with heterogeneous therapeutic approaches, we designed our study to determine T4 requirement in the same patients and treatment settings, before and after total thyroidectomy.

DESIGN, PATIENTS AND METHODS

This was a longitudinal study including 23 goitrous patients treated with T4 in an individually tailored fashion. All patients exhibited a stable TSH (median TSH = 0.28 mU/l) at a stable T4 dose for at least 1 year before surgery (median T4 dose = 1.50 μg/kg per day). The patients underwent total thyroidectomy based on cancer suspicion or compressive symptoms. Eventually diagnosed as having DTC (pT1b-pT2N0) and following surgical and radiometabolic treatment, they were treated with the same pre-surgical doses of T4.

RESULTS

Three months after surgery,using the same pre-surgical dose, median TSH increased up to 5.38 mU/l (P<0.0001) and so the T4 dose had to be increased (median T4 dose = 1.95 μg/kg per day; +30%; P < 0.0001). Once divided by patients' age, we observed that, after thyroidectomy and maintaining the same pre-surgical dose, serum TSH significantly increased both in younger and in older patients (median TSH = 4.57 and 6.11 mU/l respectively). Serum TSH was restored to the pre-surgical level by increasing the dose up to 1.95 and 1.77 μg/kg per day (+25 and +21%) respectively.

CONCLUSIONS

Following the same treatment regimen, a thyroidectomized patient requires one-third higher therapeutic T4 dose than before surgery. Despite this increase, the dose of T4 needed in our patients remains significantly lower than that previously described in athyreotic patients.

A systematic review of randomized controlled trials for management of persistent post-treatment fatigue in thyroid cancer survivors

BACKGROUND

Fatigue that persists post-treatment is commonly reported by thyroid cancer (TC) survivors.

METHODS

A systematic review of published English language randomized controlled trials (RCTs) on interventions for management of persistent post-treatment fatigue in TC was conducted. This review excluded studies on short-term interventions used in preparation for radioactive iodine diagnostic scans or treatment. An electronic search was executed in six databases and supplemented by a hand search. Two reviewers independently reviewed all citations from the electronic search and relevant full-text studies. Two abstractors independently critically appraised included studies and abstracted the data. The data were qualitatively summarized.

RESULTS

A total of 1086 unique citations and 25 full-text studies were reviewed. Four studies summarizing the results of three RCTs were included. The interventions included: combination triiodothyronine with levothyroxine (L-T4) therapy compared to L-T4 alone (one RCT), reduction in degree of thyrotropin (TSH) suppression using L-T4 compared to maintenance of TSH suppression (one RCT), and supervised exercise compared to inactivity (two RCTs examining different fatigue outcomes in same population). Trial duration ranged from 10 weeks to six months. All trials had limitations, and the number of TC survivors included in respective RCTs ranged from 15 to 36. Hormonal treatment RCTs had mixed fatigue outcome results within respective trials. However, multiple measures suggesting improvement in fatigue were reported following the exercise intervention.

CONCLUSIONS

There is paucity of RCTs to guide evidence-based management of persistent post-treatment fatigue in TC survivors. RCTs of interventions for prevention or treatment of fatigue in TC survivors are needed.

Treatment of hypothyroidism with levothyroxine or a combination of levothyroxine plus L-triiodothyronine

At present, the drug of choice for the treatment of hypothyroidism is levothyroxine sodium, even though the thyroid gland secretes both thyroxine and 3',3,5-triiodothyronine; the latter is the more active of the two at the cellular level because of its higher affinity for the nuclear thyroid hormone receptors. To date, combined levothyroxine plus liothyronine treatment for hypothyroidism has been evaluated in 15 clinical trials in humans. In two studies, combined therapy seemed to have beneficial effects on mood, quality of life, and psychometric performance of patients, compared with levothyroxine alone; in some of these studies, the patients preferred levothyroxine plus liothyronine combinations. This preference should be balanced against the possibility of adverse events resulting from the addition of liothyronine to levothyroxine. Until clear advantages of levothyroxine plus liothyronine are demonstrated, the administration of levothyroxine alone should remain the treatment of choice for replacement therapy of hypothyroidism.

Guidelines for the treatment of hypothyroidism: prepared by the american thyroid association task force on thyroid hormone replacement

BACKGROUND

A number of recent advances in our understanding of thyroid physiology may shed light on why some patients feel unwell while taking levothyroxine monotherapy. The purpose of this task force was to review the goals of levothyroxine therapy, the optimal prescription of conventional levothyroxine therapy, the sources of dissatisfaction with levothyroxine therapy, the evidence on treatment alternatives, and the relevant knowledge gaps. We wished to determine whether there are sufficient new data generated by well-designed studies to provide reason to pursue such therapies and change the current standard of care. This document is intended to inform clinical decision-making on thyroid hormone replacement therapy; it is not a replacement for individualized clinical judgment.

METHODS

Task force members identified 24 questions relevant to the treatment of hypothyroidism. The clinical literature relating to each question was then reviewed. Clinical reviews were supplemented, when relevant, with related mechanistic and bench research literature reviews, performed by our team of translational scientists. Ethics reviews were provided, when relevant, by a bioethicist. The responses to questions were formatted, when possible, in the form of a formal clinical recommendation statement. When responses were not suitable for a formal clinical recommendation, a summary response statement without a formal clinical recommendation was developed. For clinical recommendations, the supporting evidence was appraised, and the strength of each clinical recommendation was assessed, using the American College of Physicians system. The final document was organized so that each topic is introduced with a question, followed by a formal clinical recommendation. Stakeholder input was received at a national meeting, with some subsequent refinement of the clinical questions addressed in the document. Consensus was achieved for all recommendations by the task force.

RESULTS

We reviewed the following therapeutic categories: (i) levothyroxine therapy, (ii) non-levothyroxine-based thyroid hormone therapies, and (iii) use of thyroid hormone analogs. The second category included thyroid extracts, synthetic combination therapy, triiodothyronine therapy, and compounded thyroid hormones.

CONCLUSIONS

We concluded that levothyroxine should remain the standard of care for treating hypothyroidism. We found no consistently strong evidence for the superiority of alternative preparations (e.g., levothyroxine-liothyronine combination therapy, or thyroid extract therapy, or others) over monotherapy with levothyroxine, in improving health outcomes. Some examples of future research needs include the development of superior biomarkers of euthyroidism to supplement thyrotropin measurements, mechanistic research on serum triiodothyronine levels (including effects of age and disease status, relationship with tissue concentrations, as well as potential therapeutic targeting), and long-term outcome clinical trials testing combination therapy or thyroid extracts (including subgroup effects). Additional research is also needed to develop thyroid hormone analogs with a favorable benefit to risk profile.

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.

Persistent posttreatment fatigue in thyroid cancer survivors: a scoping review

The relevance of persistent posttreatment fatigue (PPF) to thyroid cancer (TC) survivor populations is not known. This article presents a scoping review, which is an overview of published research activity. Uncontrolled data suggest that PPF is one of the most common complaints in TC survivors. Furthermore, statistically significantly worse levels of fatigue were reported in TC survivors, compared with the general population or healthy controls. There was some inconsistency among PPF risk factors. More research is needed on PPF in TC survivors, including long-term prospective cohort studies, research on fatigue severity prevalence, and randomized controlled trials of treatment strategies.

Fatigue among short- and long-term thyroid cancer survivors: results from the population-based PROFILES registry

BACKGROUND

The aims of this study were (i) to obtain insight into the prevalence of fatigue among short- and long-term thyroid cancer (TC) survivors, by comparing a sample of TC survivors with an age- and sex-matched normative population, and (ii) to investigate which demographic, clinical, and TC-specific health-related quality of life (HRQoL) characteristics were associated with fatigue.

METHODS

All patients found to have TC between 1990 and 2008, as registered in the Eindhoven Cancer Registry, received a cross-sectional survey on fatigue (Fatigue Assessment Scale), TC-specific HRQoL (THYCA-QoL), and psychological distress (Hospital Anxiety and Depression Scale). The fatigue scores were compared with those of an age- and sex-matched normative population (n=530). Multiple logistic regression analyses were conducted to investigate the independent associations between clinical and demographic characteristics, TC-specific HRQoL, and psychological distress with fatigue.

RESULTS

Eighty-six percent (n=306) responded. TC survivors were more often classified as fatigued or very fatigued (short-term <5 years: 43%; long-term 5-10 years: 44%; long-term 10-15 years: 47%; long-term >15 years: 39%) compared to the normative population (25%; p<0.001). Anxiety (odds ratio (OR) 1.15, 95% confidence interval [CI] 1.03-1.28) and depression (OR 1.43 [CI 1.22-1.68]) were associated with fatigue, as was also the case for TC-specific neuromuscular (OR 1.03 [CI 1.01-1.06]), concentration (OR 1.03 [CI 1.01-1.06]), and psychological TC-specific HRQoL (OR 1.06 [CI 1.02-1.10]).

CONCLUSION

Short- and long-term TC survivors report higher levels of fatigue than an age- and sex-matched normative population do. Both TC-specific HRQoL and psychological distress were associated with fatigue.

Combination L-T3 and L-T4 therapy for hypothyroidism

PURPOSE OF REVIEW

Because of the longstanding controversy regarding whether hypothyroid patients can be optimally replaced by treatment with levothyroxine (L-T4) alone, numerous studies have addressed potential benefits of combined therapy of triiodothyronine (T3) with L-T4. Results of these studies have failed to support a potential benefit of combined therapy. A strong argument for the addition of L-T3 to L-T4 monotherapy has been lacking until recent genetic studies indicated a rationale for such therapy among a small fraction of the hypothyroid patient population.

RECENT FINDINGS

Interest in this issue has focused on the importance of the deiodinases in maintaining the euthyroid state and the role of genetic polymorphisms in the deiodinase genes that would affect thyroid hormone concentrations in both blood and tissues. One such polymorphism in the D2 gene, Thr92Ala, is associated with reduced T4 to T3 activation in skeletal muscle and thyroid, linked to obesity and alterations in thyroid-pituitary feedback, and in responses to thyroid hormone treatment.

SUMMARY

Although our professional organizations continue to recommend L-T4 alone for the treatment of hypothyroidism, the possibility of a D2 gene polymorphism should be considered in patients on L-T4 monotherapy who continue to complain of fatigue in spite of dosage achieving low normal serum thyroid stimulating hormone levels. A suggestive clue to the presence of this polymorphism could be a higher than normal free T4/free T3 ratio. Clinicians could consider adding T3 as a therapeutic trial in selected patients. Future well controlled clinical trials will be required to more fully resolve the controversy.

Combination treatment with T4 and T3: toward personalized replacement therapy in hypothyroidism?

CONTEXT

Levothyroxine therapy is the traditional lifelong replacement therapy for hypothyroid patients. Over the last several years, new evidence has led clinicians to evaluate the option of combined T(3) and T(4) treatment to improve the quality of life, cognition, and peripheral parameters of thyroid hormone action in hypothyroidism. The aim of this review is to assess the physiological basis and the results of current studies on this topic.

EVIDENCE ACQUISITION

We searched Medline for reports published with the following search terms: hypothyroidism, levothyroxine, triiodothyronine, thyroid, guidelines, treatment, deiodinases, clinical symptoms, quality of life, cognition, mood, depression, body weight, heart rate, cholesterol, bone markers, SHBG, and patient preference for combined therapy. The search was restricted to reports published in English since 1970, but some reports published before 1970 were also incorporated. We supplemented the search with records from personal files and references of relevant articles and textbooks. Parameters analyzed included the rationale for combination treatment, the type of patients to be selected, the optimal T(4)/T(3) ratio, and the potential benefits of this therapy on symptoms of hypothyroidism, quality of life, mood, cognition, and peripheral parameters of thyroid hormone action.

EVIDENCE SYNTHESIS

The outcome of our analysis suggests that it may be time to consider a personalized regimen of thyroid hormone replacement therapy in hypothyroid patients.

CONCLUSIONS

Further prospective randomized controlled studies are needed to clarify this important issue. Innovative formulations of the thyroid hormones will be required to mimic a more perfect thyroid hormone replacement therapy than is currently available.