What’s covered?

What is subclinical hypothyroidism?

An overview

Subclinical hypothyroidism (sHypo) is a condition in which the free thyroxine level is normal in serum while the thyroid stimulating hormone level is elevated.

Subclinical hypothyroidism is a widespread condition with various distinctive characteristics that are seen in clinical settings. Instead of using a worldwide reference range for TSH that is based on the 95% confidence interval of a healthy population, its diagnosis should be based on knowledge of geographic and demographic variances in biochemical criteria.

The focus should be on persistent or advancing forms, which are primarily caused by chronic autoimmune thyroiditis, rather than the majority of sHypo instances, which are temporary and reversible. This is vital to keep in mind when making the diagnostic evaluation.

A form of the thyroid control panel is made up of your thyroid gland, pituitary gland, and hypothalamus, which are all located in your brain. They create a substance known as thyroid-stimulating hormone (TSH). Triiodothyronine, also known as T3, and thyroxine are the two primary thyroid hormones that are stimulated by the TSH hormone.

TSH stimulates the thyroid to create T3 or T4 when it is released. More TSH is released when T3 or T4 levels in the body are insufficient; less TSH is released when T3 or T4 levels are adequate or excessive. It has a well-balanced feedback mechanism.

When something goes wrong with this mechanism, the thyroid stops generating sufficient thyroid hormone to fulfil the body's needs, which is known as hypothyroidism or subclinical hypothyroidism.

Your thyroid has a significant impact on your general health, affecting both your metabolism and your mood. Numerous health problems, ranging from weariness and joint discomfort to problems with fertility and heart disease, can be brought on by abnormal thyroid hormone levels. Thus, the little thyroid gland at the bottom of your neck has a significant function.

Causes of subclinical hypothyroidism

Some of the main causes related to subclinical hypothyroidism are listed below.

A major reason for hypothyroidism is Hashimoto's thyroiditis. Your immune system targets body tissues, particularly the thyroid gland, leading to this autoimmune illness. Your risk is increased if you have a family history of autoimmune thyroid disease. Although the exact mechanism is unknown, external conditions can also cause autoimmune illness.

Your thyroid function may be affected by several medications, including certain corticosteroids, painkillers, and neurologic and cardiac treatments.

It's possible that excessive radioactive iodine or antithyroid medication used to treat your earlier hyperthyroidism (overactive thyroid) caused you to develop hypothyroidism or subclinical hypothyroidism. The thyroid may also be affected by radiation therapy used to treat cancer in the head or neck region.

A thyroidectomy, or partial removal of the thyroid gland, is usually necessary for the treatment of certain thyroid disorders, such as thyroid cancer and thyroid nodules. Thyroidectomy can result in subclinical or unsubtle hypothyroidism depending on the amount of the gland removed.

Radioactive iodine, which can damage the thyroid, is occasionally used to treat or provide to patients with Graves' disease, nodular goitre, or thyroid cancer. The breakdown of the radioactive iodine may lead to hypothyroidism. Radiation therapy can damage the thyroid in some people with Hodgkin's disease, lymphoma, or head and neck malignancies, leading to hypothyroidism.

Iodine is needed in the thyroid for the synthesis of thyroid hormone. Excellent sources of iodine include seafood, seaweed, plants grown in iodine-rich soil, and iodized salt. Iodine consumption must be sufficient to produce thyroid hormones at optimal levels. Iodine deficiency can lead to hypothyroidism, but iodine overdose can exacerbate the illness.

Risk factors for hypothyroidism

The structure and physiology of the thyroid are significantly influenced by ageing. Age-related changes in anatomy include decreased follicle size and weight, as well as enhanced rigidity and lymphocytic infiltration. The thyroid hormone's half-life significantly lengthens with age, and its production itself may decline; nevertheless, this is not a known cause of thyroid dysfunction unless there is already a thyroid disorder present.

The most likely cause of sHypo in ageing people is chronic autoimmune thyroiditis (CAT). Especially given that the reduction in thyroid function is gradual, sHypo may go undiagnosed since the symptoms may be mistakenly dismissed as a result of ageing. Research has shown that older persons with chronic sHypo did not have increased risks of cardiovascular death, heart failure, coronary artery disease, or cognitive impairment.

Thyroid hormone plays special roles in children, including maturational effects on brain development in the first three years of life and effects on linear growth that last until adolescent epiphyseal closure. In comparison to teens, younger children's cases of schizophrenia are more likely to be idiopathic or hereditary.

Women are more likely than males to have sHypo, which is partly because CAT is more common in women and oestrogen levels are higher in women. Increased metabolic demands during pregnancy affect the thyroid-pituitary system. Pregnancy is characterized by a decrease in the lower and upper limits of TSH, usually in the first trimester due to the direct stimulation of the TSH receptor by increased serum levels of human chorionic gonadotropin.

The TSH reference range rises throughout the second and third trimesters, although it stays below that of normal non-pregnant women. Depending on iodine intake and the various ethnic groups, this reduction's severity varies.

The mother and foetus should be regarded as being in danger of overt hypothyroidism during pregnancy. sHypo during pregnancy is linked to several detrimental effects for both the mother and the baby.

It would be advisable to actively treat sHypo in women who are having in vitro fertilization or intending to birth, or even in all women of childbearing age, because of worries about the negative consequences of pregnancy.

sHypo is associated with impaired exercise-induced ventricular filling, decreased relaxation time, and impaired diastolic function of the left ventricle (LV), which results in LV systolic dysfunction.

Patients with sHypo have also been documented to have circulatory problems. A meta-analysis revealed that grade 2 sHypo was linked to thicker carotid endothelium. However, clinical data do not support these diagnostic and analytical findings. A thorough meta-analysis that showed a connection between the risk of cardiovascular disease and sHypo was one of many types of research that discovered links between sHypo and the condition.

In comparison to the general population, end-stage renal illness has been found to have a greater prevalence of sHypo. In individuals with renal failure requiring haemodialysis, sHypo was linked to greater mortality than the euthyroid condition. These findings proved that sHypo aggravates the clinical progression of CKD.

Symptoms of Subclinical hypothyroidism

Subclinical hypothyroidism may not show any symptoms when TSH levels are very slightly high.

But if you do experience mild hypothyroid symptoms, you can anticipate the following:

• Difficulty with mood or depression

• Fatigue

• Gaining weight

• Feeling of being cold despite wearing warm clothing

• Gastrointestinal problems, such as constipation

• A goitre, also known as an enlarged thyroid gland, can be felt as a lump or swelling in the front of the neck.

Diagnose and test for subclinical hypothyroidism

Thyroid function tests are the only basis for the evaluation of subclinical hypothyroidism.

TSH, also known as thyrotropin, has a normal test range for non-pregnant adults of 0.4 to 4.5 mIU/L. Each trimester has a different normal range for TSH levels in pregnant women.

You have subclinical hypothyroidism if you have thyroid blood tests and the findings show that your TSH levels are increased (5 to 10 mIU/L) while your thyroxine (T4) levels are within the normal range.

Treatment and management of subclinical hypothyroidism

A path for medical decisions for sHypo has been provided by several clinical guidelines. These recommendations mainly take into account the patient's age and serum TSH levels. For guidance, other criteria such as the existence of symptoms, cardiovascular disease risk factors, and goitre should also be added.

Subclinical hypothyroidism cannot be cured by self-treatment, however, it frequently resolves on its own over time. Other than that, medicine can treat subclinical hypothyroidism, but doctors don't usually advise it. Your doctor will give you the thyroid hormone replacement drug levothyroxine if they recommend treatment for subclinical hypothyroidism. It is offered as tablets. If your test results reveal you have subclinical hypothyroidism, your healthcare professionals will typically follow a wait-and-see strategy.

Speak with your healthcare practitioner if you start to suffer hypothyroidism symptoms including fatigue and unexplained weight gain. To determine whether you have overt hypothyroidism, they'll probably need another thyroid blood test.

Within three months of the initial abnormal test result, your doctor may request another blood test to assess your TSH levels before beginning levothyroxine therapy in subclinical hypothyroidism. This is because, after three months, the TSH level normalizes in roughly 60% of patients.

To ensure that your thyroid levels are in a healthy range while taking medication, your doctor probably wants you to undergo routine blood testing. Hyperthyroidism may result from taking too much levothyroxine. Most of the time, there is absolutely nothing you can do to stop overt or subclinical hypothyroidism.

But if you don't consume enough iodine, you may experience subclinical or overt hypothyroidism. This is so that your thyroid can produce thyroid hormone, which depends on iodine. Iodine deficiency is the most typical reason for hypothyroidism worldwide.

Complications of subclinical hypothyroidism

Low-density lipoprotein (LDL) cholesterol levels can be elevated in those who have an underactive thyroid. As a result, the arteries will accumulate fat, which will impede blood flow. Significant heart issues result from this.

Myxoedema, a potentially lethal illness, can occasionally be brought on by a thyroid that is severely underactive. When thyroid hormone levels reach this point, they start to fall and cause symptoms like confusion, cold, and drowsiness.

The luteal phase defect, high prolactin levels, and sex hormone abnormalities are all examples of which thyroid disease can have a detrimental effect on fertility.

Infertility rates are low in hypothyroid women. However, even if a patient does become pregnant, there is still an increased risk that the pregnancy would end in postpartum haemorrhage, gestational hypertension, anaemia, and abruptio placenta. These problems are more likely to occur in women with clinically evident hypothyroidism than in those with subclinical hypothyroidism.

A goitre, often known as a throat lump, is brought on by an abnormal thyroid gland enlargement. The body's efforts to increase thyroid hormone production can cause goitres in people with an underactive thyroid.

Conclusion

If you are worried about subclinical hypothyroidism or are at risk for it, you should get it tested which can be done easily; otherwise, you should speak to your doctor about it.