Subclinical Hypothyroidism: Symptoms, Causes, Diagnosis, and Treatment

Subclinical hypothyroidism is characterised by increased thyroid-stimulating hormone levels, while thyroxine levels remain normal. This condition may be associated with an autoimmune disorder or thyroid surgery. 

This article provides detailed insights into the subclinical hypothyroidism symptoms, causes, risk factors, diagnosis, treatment methods, and more.

What are the Key Causes of Subclinical Hypothyroidism?

Multiple glands and hormones in the endocrine system regulate TSH (thyroid-stimulating hormone) levels in the circulation. First, the hypothalamus secretes thyroid-releasing hormone (TRH), which stimulates the pituitary gland to produce TSH.

Then, TSH induces thyroid cells to create 80% T4 (thyroxine) and 20% T3 (triiodothyronine) in the blood. When both of these hormones reach their peak levels, the pituitary gland halts TSH synthesis and repeats the cycle until their levels fall.

Subclinical hypothyroidism is caused by thyroid inflammation or abnormalities that disrupt the hormone production cycle. As a result, despite the elevated TSH levels that produce this syndrome, the T4 hormone level remains normal.

What are the Risk Factors of Subclinical Hypothyroidism?

Most of the risk factors for subclinical hypothyroidism are difficult to control. Some of them are listed below:

• Age

Thyroid-stimulating hormone levels rise with age, perhaps leading to subclinical hypothyroidism in elderly people.

• Gender

According to the Journal of Endocrinology and Metabolism, estrogen (female hormone) has an important role in the development of subclinical hypothyroidism, though this is not mentioned explicitly. Women are more likely than men to have subclinical hypothyroidism.

• Iodine Intake

Iodine is required for proper thyroid function, but only in restricted amounts. Excessive iodine consumption might raise the risk of subclinical hypothyroidism.

List of the Key Symptoms of Subclinical Hypothyroidism

Subclinical hypothyroidism usually has no symptoms. This is especially true when the TSH (thyroid-stimulating hormone) levels are just slightly increased. When symptoms do appear, they tend to be nonspecific and generic, including:

• Depression
• Constipation
• Fatigue
• Goitre (this appears as swelling in the front of the neck due to an enlarged thyroid gland)
• Weight gain
• Hair loss
• Cold intolerance

How to Conduct Subclinical Hypothyroidism Diagnosis?

Thyroid function blood tests are the most common method for diagnosing subclinical hypothyroidism. It helps in determining the appropriate level of thyroid-stimulating hormone (TSH) in the body, which allows for the detection of subclinical hypothyroidism.

A person's normal TSH level ranges from 0.4 to 4.5 mIU/L. However, it may change depending on the trimester of pregnancy. If an individual's blood test results indicate normal T4 levels but elevated TSH (thyroid-stimulating hormone) levels ranging from 5 to 10 mIU/L,  then they may have subclinical hypothyroidism.

Subclinical hypothyroidism is classified into two groups based on TSH levels:

• Grade 1: TSH level ranges from 4.5 to 9.9 mIU/L.

• Grade 2: TSH levels are 10 mIU/L or higher.

Note that in 90% of cases, individuals are classified with Grade 1 subclinical hypothyroidism.

Several non-thyroid factors can cause a rise in TSH levels. To prevent misdiagnosing subclinical hypothyroidism in such cases, one must understand these factors:

• Ageing is connected with an increase in TSH levels
• Non-thyroidal illness
• Chronic renal failure
• Certain medications such as lithium, amphetamine, ritonavir, metoclopramide

What is the Impact of Subclinical Hypothyroidism on Health?

Subclinical hypothyroidism can have a number of impacts on health, which are:

• Cardiovascular Disease: Subclinical hypothyroidism is linked with a higher risk of coronary artery disease (CAD), congestive heart failure, and stroke. It can also affect blood pressure and cholesterol levels.
• Cognitive Impairment: Some studies indicate that subclinical hypothyroidism may be associated with cognitive impairment, such as memory issues.
• Neuromuscular Abnormalities: It may be associated with neuromuscular disorders such as muscle weakness in the body.
• Reproductive Abnormalities: This disease might raise the risk of miscarriage or early delivery during pregnancy.

What are the Treatment Options for Subclinical Hypothyroidism?

Subclinical hypothyroidism is treated by doctors using levothyroxine, a thyroid hormone replacement treatment.
The American Thyroid Association (ATA) and the American Association of Clinical Endocrinology suggest that patients begin levothyroxine medication if they satisfy the following criteria:

• TSH levels above 10 mIU/L 
• Hypothyroid symptoms 
• Cardiovascular risk factors
• Positive TPO antibody

For persons without cardiovascular disease, the beginning dose of levothyroxine is 1.6 mcg/kg. For those with cardiovascular problems, the beginning dose is 25 mcg/kg.

In pregnancy

During the first three months of pregnancy, the fetus relies on the pregnant person's thyroid hormones to build its brain and nervous system. A shortage of thyroid hormone during pregnancy might result in poor developmental results as well as difficulties for the pregnant woman.

The ATA (American Thyroid Association) states that pregnant women should take their thyroxine dose as prescribed since it is safe for both of them. If a pregnant person is diagnosed with subclinical hypothyroidism, they must begin therapy immediately and maintain it until delivery.

Importance of Lifestyle Changes and Proper Management in Subclinical Hypothyroidism

Hypothyroidism is the most common thyroid condition, and its frequency is rising nowadays. Dietary and lifestyle adjustments can help manage and control thyroid-related diseases. 

Thyroid problems are frequently caused by a poor diet, stress, and other lifestyle factors. A few adjustments that can help in controlling the thyroid disease include:

• Eating less sugar
• Exercising daily
• Adding  vitamins and minerals to the diet
• Controlling alcohol intake
• Meditation

Conclusion

Subclinical hypothyroidism is a thyroid condition that typically appears without symptoms but can have serious health consequences if left untreated. Early detection, adequate therapy, and lifestyle changes can help manage the illness and avoid its effects. Therefore, regular monitoring and consultation with doctors are required for the best results.