Subclinical Thyroid Dysfunction - Causes, Symptoms, and Treatment

Introduction:

The thyroid gland is a small butterfly-shaped gland located in the lower neck. It produces two important hormones, T3 (triiodothyronine) and T4 (thyroxine), that have many pivotal roles, like regulating the body's heart and brain functions and metabolism. The pituitary gland, also known as the "master gland," located at the base of the brain, secretes a hormone called thyroid-stimulating hormone (TSH). TSH reaches the thyroid gland in the neck through the bloodstream and directs it to produce the thyroid hormones T3 and T4. Therefore, TSH is released by the pituitary gland whenever the body senses a lowering of the thyroid hormonal levels. Iodine is required to produce thyroid hormones, which are available through foods.

What Is Subclinical Thyroid Dysfunction?

Subclinical thyroid dysfunction, also called subclinical hypothyroidism, is an early and mild form of hypothyroidism in which the circulating levels of the hormone TSH are slightly elevated. However, the levels of thyroid gland hormones T3 and T4 are within the normal laboratory ranges. According to research, about three to eight percent of people have subclinical thyroid dysplasia. Also, 26.8 percent of cases with subclinical thyroid dysfunction tend to develop hypothyroidism within six years. As thyroid hormones play a vital role in many body functions, an imbalance in their levels can affect several functions.

Subclinical thyroid dysfunction is more common in women when compared to men. In addition, women of child-bearing ages tend to develop it. Some studies have shown an increased risk of heart failure, disorders like anxiety and depression, and neuromuscular disorders more commonly associated with subclinical thyroid dysfunction. Also, it was noted that elderly postmenopausal women with subclinical thyroid dysfunction had increased chances of developing osteoporosis (thin and weak bones prone to fractures) later in life.

What Are the Causes of Subclinical Thyroid Dysfunction?

Both subclinical thyroid dysfunction, and hypothyroidism share similar causes, as the condition has a slightly elevated TSH level, with T3 and T4 levels within a normal range. The causes include:

1. A family history of an autoimmune thyroid disease like Hashimoto's disease. Autoimmune thyroid disease is when the body's immune system attacks and destroys the thyroid cells.

2. An injury to or accidental removal of some thyroid tissue that occurs during head and neck surgery.

3. Use of radioactive iodine to treat hyperthyroidism, a condition in which the gland produces excessive amounts of thyroid hormones.

4. Intake of medicines containing iodine or lithium.

What Are the Risk Factors for Developing Subclinical Thyroid Dysfunction?

The factors that increase the risk of developing subclinical thyroid dysfunction include:

• Age: Older people are at a greater risk of developing the condition as the TSH levels rise in the body with age.

• Gender: Females tend to develop the condition more often than males. Research believes that the female hormone estrogen plays a role.

• Iodine Intake: Iodine is an essential element for producing thyroid hormones. People who consume excess iodine are at an increased risk for developing subclinical thyroid dysfunction.

What Are the Symptoms of Subclinical Thyroid Dysfunction?

In most cases, the symptoms of subclinical thyroid dysfunction are absent or mild. However, when they occur, the symptoms are more general. The following symptoms may be noted, that include:

• Weight gain.

• Tiredness.

• Intolerance to cold.

• Hair loss.

• Constipation.

• Depression.

• Goiter (a swelling in the front of the neck due to an enlarged thyroid gland).

As these symptoms coincide with other medical conditions, a thorough examination by a specialist doctor is necessary.

What Are the Complications of Subclinical Thyroid Dysfunction?

The complications of the condition include:

• Heart Problems: The relationship between subclinical thyroid dysfunction and heart diseases is still under research. However, it is believed that elevated TSH levels can lead to high blood pressure and cholesterol when left untreated. Also, a study has shown an increased risk of developing the condition in an older population with a TSH value greater than 7 IU/L.

• Miscarriage: Normal levels of thyroid hormones are essential in mothers for the growth and development of the fetus. A TSH value of less than 2.5 mIU/L in the first trimester and less than 3 mIU/L in the second and third trimesters are considered normal in pregnancy. However, assessing the values of antithyroid peroxidase antibodies (TPO) is also vital in determining the adverse effects of pregnancy. Therefore, it was studied that women with low TSH values and positive antithyroid antibodies had higher chances of miscarriage when compared to women with slightly higher TSH and negative antithyroid antibodies.

How Is Subclinical Thyroid Dysfunction Diagnosed?

A simple blood test diagnosis of subclinical thyroid dysplasia. The normal range of TSH in the blood is between 4.5 and 5 mIU/L. When TSH levels are higher than the normal range, T3 and T4 suggest subclinical thyroid dysfunction. A repeat of the thyroid profile test is recommended after a few months to confirm the diagnosis.

How Is Subclinical Thyroid Dysfunction Treated?

Cases of subclinical thyroid dysfunction are treated only when the levels of TSH are above 10 mIU/L, as high levels of TSH can cause ill effects on the body. However, there is still a debate on whether people with TSH values between 5.1 and 10 mIU/L require treatment. The healthcare provider decides on whether to start the treatment or wait based on the following factors, that include:

1. TSH level.

2. Age of the patient.

3. Medical history of the patient.

4. Presence of antithyroid antibodies in the blood.

5. Goiter.

6. The effect of symptoms on the patients.

Patients are treated with Levothyroxine (Levoxyl or Synthroid), a synthetic thyroid hormone. It is a well-tolerated medicine that is prescribed to be taken orally.

Conclusion:

Subclinical thyroid dysfunction is when a person has slightly elevated TSH levels, with standard T3 and T4 hormone levels. Treatment for the condition is based on the individual's age, history and symptoms. Not all patients require treatment. However, an optimal intake of iodine which is 150 micrograms per day, is recommended to help keep the thyroid gland functioning normally. Iodized table salt, dairy products, eggs, and saltwater fish are good sources of iodine. The most important way to keep the thyroid gland working normally is by consuming a nutritious and healthy diet.