Introduction:
Borderline hypothyroidism is a condition characterized by normal levels of free T4 (thyroxine) and free T3 (triiodothyronine), an increased level of thyroid-stimulating hormone (TSH). Borderline hypothyroidism is more prevalent in women and older individuals. Borderline hypothyroidism can remain asymptomatic or present with mild symptoms similar to hypothyroidism. Several risk factors like iodine deficiency, pregnancy, being a woman, history of thyroid treatment, etc., increase the chances of developing borderline hypothyroidism.
What Are Thyroid Gland and Hypothyroidism?
The thyroid is a small endocrine gland responsible for the secretion of the thyroid hormones; thyroxine (T4), triiodothyronine (T3), and calcitonin. The thyroid gland is a small endocrine gland that has a similar shape to a butterfly, and the gland presents the base of the neck. Due to several medical conditions, the thyroid can overproduce or under-produce these thyroid hormones leading to thyroid dysfunction. The pituitary gland is responsible for producing and releasing TSH (thyroid-stimulating hormone); this hormone regulates the thyroid gland's function to produce and secrete the thyroid hormones. When the thyroid gland does not synthesize and release an adequate amount of thyroid hormones, the condition is known as hypothyroidism. Hypothyroidism is characterized by symptoms like; fatigue, tiredness, sensitivity to cold, unusual weight gain, hoarseness of the voice, etc.
What Are the Thyroid Hormone Reference Ranges?
The normal reference range of various thyroid hormones are:
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Total thyroxine: 4 to 11 μm/dl.
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Free thyroxine: 8.5 to 15.5 μm/dl.
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Total triiodothyronine: 60 to 175 μm/dl.
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Free triiodothyronine: 2.3 to 4.2 μm/dl.
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Thyroid-stimulating hormone: 0.35 to 2.80 μm/dl.
Use of several medications, pregnancy, etc., can alter these values.
What Is Borderline Hypothyroidism?
Borderline hypothyroidism is a mild form of hypothyroidism characterized by slightly deranged serum levels of the thyroid-stimulating hormone and normal levels of thyroid hormones. Borderline hypothyroidism is a subclinical or milder form of hypothyroidism. However, borderline hypothyroidism may or may not develop into full-blown hypothyroidism.
What Causes Borderline Hypothyroidism?
The various causes of borderline hypothyroidism are:
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History of auto-immune conditions like Hashimoto’s thyroiditis in the family. An auto-immune condition is a medical condition in which the body’s immune system starts attacking its healthy cells (in this case, healthy thyroid cells).
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Trauma or injury to the thyroid gland.
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Radioactive iodine therapy is a treatment procedure for hyperthyroidism (overactive thyroid) in which thyroid cells are targeted.
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Use certain medications containing Lithium, Amiodarone, Iodine, Methimazole, etc.
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Pituitary gland disorders can lead to an imbalance in the levels of thyroid-stimulating hormones (TSH) (the hormone responsible for stimulating the thyroid gland to produce thyroid hormones).
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Iodine deficiency is one of the most common causes of hypothyroidism, especially in developing countries.
What Are the Symptoms of Borderline Hypothyroidism?
Signs and symptoms of borderline hypothyroidism include:
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Borderline hypothyroidism either remains asymptomatic or presents with very mild symptoms.
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Feeling tired or fatigued.
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Constipation and altered bowel movements.
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Unusual weight gain.
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Excessive hair loss.
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Intolerance to cold.
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Goiter (a lump in front of the neck due to an enlarged thyroid gland).
Who Is Affected by Borderline Hypothyroidism?
Various factors can increase the chances of developing borderline hypothyroidism, and these factors include:
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Women are at a higher risk of developing borderline hypothyroidism (like other thyroid disorders). The exact causes are unclear, but experts believe the female hormone estrogen may play a crucial role in developing borderline hypothyroidism.
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The risk of developing borderline hypothyroidism increases with age. People over the age of 60 are at a higher risk.
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Iodine deficiency, common in low socio-economic status and developing countries, is a risk factor.
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Individuals with a family history of thyroid disorders.
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Individuals with other auto-immune conditions.
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Pregnancy and post-partum time.
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Individuals who have had treatment or surgery for thyroid diseases.
How Is Borderline Hypothyroidism Diagnosed?
The diagnosis of borderline hypothyroidism includes:
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Blood Examinations: Several blood examinations are done to check the levels of thyroid hormones and the level of thyroid-stimulating hormones. In the case of borderline hypothyroidism, thyroid hormones are within the normal range, but the level of thyroid-stimulating hormone is elevated. Therefore, the blood tests should be repeated after a few months, and the hormone levels should be monitored.
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Imaging Tests: Imaging tests like CT (computed tomography) scan or MRI (magnetic resonance imaging) should be done to check for the presence of any pituitary gland abnormalities.
How Is Borderline Hypothyroidism Treated?
Treatment of borderline hypothyroidism involves the following considerations:
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The level of thyroid-stimulating hormone.
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Presence of a goiter.
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Presence of antithyroid antibodies in the blood.
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Presence and severity of the symptoms.
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Age of the patient.
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Patient’s medical history.
Individuals with thyroid-stimulating hormone levels above ten should be treated, and individuals with thyroid-stimulating hormone levels below 4.5 do not require any treatment (unless they have fertility issues). In cases where treatment is needed, thyroid hormone replacement therapy with synthetic thyroid hormones (Levothyroxine) is recommended. Online prescription of medications can also be used for treatment.
Can Borderline Hypothyroidism Lead To Hypothyroidism?
Borderline hypothyroidism can potentially turn into clinical hypothyroidism. However, in most cases, the borderline condition does progress into its clinical form. Most patients (around 62 %) with deranged thyroid-stimulating hormone levels regain normal hormone levels within five years, even without any treatment.
What Are the Complications of Borderline Hypothyroidism?
Complications associated with untreated borderline hypothyroidism are:
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Hypothyroidism: The condition can progress into full-blown clinical hypothyroidism.
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Heart Diseases: Borderline hypothyroidism, if left untreated, may play a crucial role in developing hypertension (high blood pressure) and high cholesterol. Older patients with TSH levels higher than 7mIU/L are two times more likely to develop these heart diseases.
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Infertility: Thyroid disease is a prevalent cause of infertility, and the thyroid hormones T3 and T4 play a significant role in reproductive health. If an individual is trying to conceive or is suffering infertility, treatment should be considered, especially if the TSH level is under 4.5. As the American Thyroid Association recommends, thyroperoxidase (TPO) antibodies, common in people with hypothyroidism and a sign of auto-immune thyroid disease, should be tested for in women of reproductive age with TSH values between 2.5 and 10.
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Pregnancy Loss: During the first and second trimesters, the level of thyroid-stimulating hormone in the blood is increased. The development of the fetal nervous system and brain depends on healthy thyroid hormone levels. Those who received treatment while pregnant and had a TSH level between 4.1 and 10 mIU/L had a lower miscarriage rate than women who did not get treatment. Therefore, monitoring the antithyroid antibody in the blood is critical.
Conclusion:
Borderline hypothyroidism is a milder form of hypothyroidism, but the condition does not always progress to its clinical form. However, the condition seldom requires treatment and has a good prognosis. Unfortunately, there is a lack of enough studies and research on the subject; therefore, a particular and fixed treatment plan for the condition is unavailable. The best approach to treat borderline hypothyroidism is to plan the treatment modalities uniquely for each patient after studying their medical history, family history, symptoms, etc.
