Can Reverse T3 Assay Be Employed to Guide T4 vs. T4/T3 Therapy in Hypothyroidism?

Triiodothyronine/Thyroxine Ratio as a Marker of Clinical Response to Levothyroxine Replacement in Patients With Hypothyroidism

BACKGROUND

 Hypothyroidism is one of the most common endocrine disorders with a simple therapy, that is levothyroxine (LT4). A normal thyroid-stimulating hormone (TSH) measurement is used as a marker of optimal replacement. But, many patients still have symptoms. Triiodothyronine (T3), thyroxine (T4), and their ratio may correlate with clinical improvement. The study aims to assess the T3/T4 ratio as a marker of clinical response in patients with hypothyroidism.  Method: A cross-sectional study was conducted from June to November 2022 at Faiha Specialized Diabetes, Endocrine, and Metabolism Center, in Basrah, southern Iraq. We included 48 adult patients with primary hypothyroidism on LT4 treatment only and TSH within the target reference range for at least within the last six months. Each patient was subjected to a questionnaire that was designed to capture hypothyroidism-related complaints in the form of a five-point Likert scale. Biochemical assessments were done with the measurement of TSH, T3, and T4.

RESULTS

Despite having a normal TSH level, nearly all the patients had persistent and varying severity of clinical complaints of hypothyroidism. Tiredness, hair problems, weight gain, and cold intolerance were the most severely persistent symptoms. Patients with scores of two and more for weight gain, cold intolerance, and skin problems had significantly lower T3/T4 ratios (P = 0.04, 0.002, and 0.02, respectively), while in the remaining clinical symptoms, the T3/T4 ratio did not differ significantly.

CONCLUSION

A low T3/T4 ratio was significantly associated with resistant symptoms of hypothyroidism and may be used as a marker for treatment efficacy with TSH rather than TSH value alone.

A Case-Control Study of the Relationship Between Genetic Polymorphism and Cretinism in Xinjiang

Background

Cretinism is a subtype of congenital hypothyroidism, an endocrine disorder resulting from inadequate thyroid hormone production or receptor deficiency. Genetic abnormalities play a major role in the development of thyroid dysfunction.

Methods

We recruited 183 participants with cretinism and 119 healthy participants from the Xinjiang Uyghur Autonomous Region and randomly selected 29 tag single nucleotide polymorphisms (tSNPs) in TSHB, PAX8, TPO, NKX2-5, and TSHR in all participants. We compared genotype and allele frequencies between cases and controls utilizing the chi-squared test, logistic regression analysis, and haplotype analysis.

Results

Using the chi-squared test, a single SNP was found to be associated with cretinism (recessive model: rs3754363, OR = 0.46, 95% CI = 0.27-0.80, P = 0.00519; genotype model: P = 0.01677). We stratified neurological, myxedematous, and mixed type and determined that another SNP was associated with a higher risk when comparing myxedematous type to the neurological type (rs2277923).

Conclusion

rs3754363 has a statistically significant protective effect on people with cretinism, while rs2277923 may play a greater role in promoting the development of neurocretinism.

Gut microbiota short-chain fatty acids and their impact on the host thyroid function and diseases

Thyroid disorders are clinically characterized by alterations of L-3,5,3',5'-tetraiodothyronine (T4), L-3,5,3'-triiodothyronine (T3), and/or thyroid-stimulating hormone (TSH) levels in the blood. The most frequent thyroid disorders are hypothyroidism, hyperthyroidism, and hypothyroxinemia. These conditions affect cell differentiation, function, and metabolism. It has been reported that 40% of the world's population suffers from some type of thyroid disorder and that several factors increase susceptibility to these diseases. Among them are iodine intake, environmental contamination, smoking, certain drugs, and genetic factors. Recently, the intestinal microbiota, composed of more than trillions of microbes, has emerged as a critical player in human health, and dysbiosis has been linked to thyroid diseases. The intestinal microbiota can affect host physiology by producing metabolites derived from dietary fiber, such as short-chain fatty acids (SCFAs). SCFAs have local actions in the intestine and can affect the central nervous system and immune system. Modulation of SCFAs-producing bacteria has also been connected to metabolic diseases, such as obesity and diabetes. In this review, we discuss how alterations in the production of SCFAs due to dysbiosis in patients could be related to thyroid disorders. The studies reviewed here may be of significant interest to endocrinology researchers and medical practitioners.

Suicide Attempt With Levothyroxine Overdose

Symptoms of levothyroxine overdose may vary depending on age, metabolism, etc. There are no specific guidelines for treating levothyroxine poisoning. Here, we present the case of a 69-year-old man with a history of panhypopituitarism, hypertension, and end-stage renal disease who attempted suicide by ingesting 60 tablets of 150 µg levothyroxine (9 mg). Upon presentation to the emergency room, he was asymptomatic despite the free thyroxine level above the range of the assay. During the hospital stay, he developed sinus tachycardia, which was controlled with propranolol. Mild elevations in liver enzymes were also noted. He received stress-dose steroids; hemodialysis was performed a day earlier, and cholestyramine was administered. Thyroid hormone levels started to improve by day seven and finally normalized in 20 days, after which the home dose of levothyroxine was resumed. The human body has several mechanisms to compensate for levothyroxine toxicity, including the conversion of excess levothyroxine to inactive reverse triiodothyronine, increased binding to thyroid-binding globulin, and hepatic metabolism. This case shows that it is possible to have no symptoms even with an overdose of up to 9 mg a day of levothyroxine. Signs and symptoms of levothyroxine toxicity may not appear for several days after ingestion, and, therefore, close observation preferably on a telemetry floor is recommended until the thyroid hormone levels start to decrease. Effective treatment options include beta-blockers preferably propranolol, early gastric lavage, cholestyramine, and glucocorticoids. While hemodialysis has a limited role, antithyroid drugs and activated charcoal are ineffective.

Advantages of monitoring rT3 and dividing LT3 dose in the treatment of consumptive hypothyroidism associated with infantile hepatic hemangioma

OBJECTIVES

In consumptive hypothyroidism associated with infantile hepatic hemangiomas (IHH), elevated reverse triiodothyronine (rT3) is known due to elevated D3. This report shows that rT3 is a new indicator of IHH progression and that three divided doses of LT3 per day were more effective than a single dose.

CASE PRESENTATION

A 23 day-old boy was diagnosed with diffuse IHH and severe hypothyroidism with high rT3. Propranolol and LT4 were administered. Hemangiomas gradually diminished and rT3 decreased, but the thyroid-stimulating hormone remained elevated, and free triiodothyronine (fT3) did not normalize after 2 weeks of treatment. Liothyronine (LT3) was started as a single dose and then divided into three doses after 1 week, which stabilized thyroid function.

CONCLUSIONS

rT3 levels were less variable and decreased in conjunction with tumor shrinkage; thus, rT3 is an indicator of therapeutic outcomes for IHH. LT3 administered in divided doses aided in managing IHH-associated hypothyroidism.

Physiological Role and Use of Thyroid Hormone Metabolites - Potential Utility in COVID-19 Patients

Thyroxine and triiodothyronine (T3) are classical thyroid hormones and with relatively well-understood actions. In contrast, the physiological role of thyroid hormone metabolites, also circulating in the blood, is less well characterized. These molecules, namely, reverse triiodothyronine, 3,5-diiodothyronine, 3-iodothyronamine, tetraiodoacetic acid and triiodoacetic acid, mediate both agonistic (thyromimetic) and antagonistic actions additional to the effects of the classical thyroid hormones. Here, we provide an overview of the main factors influencing thyroid hormone action, and then go on to describe the main effects of the metabolites and their potential use in medicine. One section addresses thyroid hormone levels in corona virus disease 19 (COVID-19). It appears that i) the more potently-acting molecules T3 and triiodoacetic acid have shorter half-lives than the less potent antagonists 3-iodothyronamine and tetraiodoacetic acid; ii) reverse T3 and 3,5-diiodothyronine may serve as indicators for metabolic dysregulation and disease, and iii) Nanotetrac may be a promising candidate for treating cancer, and resmetirom and VK2809 for steatohepatitis. Further, the use of L-T3 in the treatment of severely ill COVID-19 patients is critically discussed.

Hypothyroidism with elevated pancreatic amylase and lipase without clinical symptoms: A case report

BACKGROUND

Hypothyroidism is an endocrine disorder that has worldwide prevalence and can affect multiple organ systems. We report a case of hypothyroidism with elevated pancreatic amylase and trypsin without acute pancreatitis. No such case has been previously reported.

CASE SUMMARY

A 29-year-old woman did not pay much attention to a fever 4 d prior. During this time, she experienced anorexia and only drank a small amount of water every day. She did not present with abdominal distension, postprandial nausea, vomiting, cough or expectoration. After physical and laboratory examinations, the patient was diagnosed with hypothyroidism. During the course of the disease, hypothyroidism was generally accompanied by constantly increased pancreatic amylase and trypsin. After admission, the possible etiology of the patient was excluded and the concentrations of pancreatic lipase and amylase in serum were > 2000U/L (reference range 23-300 U/L) and 410 U/L (reference range 30-110 U/L), respectively. So we highly suspected that it may be acute pancreatitis. Interestingly, she never developed any complications associated with acute pancreatitis despite high levels of serum pancreatic amylase and trypsin, and she reported no symptoms of abdominal pain. Serum amylase and lipase decreased gradually after active thyroxine supplementation, and the patient was discharged from the hospital after active treatment.

CONCLUSION

This case suggests that clinicians should pay attention to hypothyroidism with elevated pancreatic amylase and trypsin, even if no complications of acute pancreatitis are reported.