The thyroid gland is an endocrine gland located in the front of the trachea. It consists of two lobes connected by the isthmus. Blood flows into the thyroid through the superior thyroid artery and inferior thyroid artery, which are branches of the external carotid artery and subclavian artery, respectively. Behind the thyroid gland, there are multiple sets of parathyroid glands (usually four sets), which are responsible for regulating calcium levels in the blood. Additionally, the recurrent laryngeal nerve (a branch of the vagus nerve, the tenth cranial nerve in humans) passes through the tracheoesophageal groove behind the thyroid gland. Therefore, during surgery, the doctor needs to be cautious to avoid damaging this nerve, as it could lead to postoperative complications such as hoarseness.

The function of the thyroid gland is to produce thyroid hormones, which are essential for maintaining our body’s metabolic functions. Thyroid hormones are hormones that stimulate our body’s cells to produce proteins. They directly influence metabolism, as well as the function and activities of various organs. Thyroid hormones play a role in regulating heart rate, blood pressure, digestion, appetite, mood fluctuations, bone metabolism, menstrual cycles, energy metabolism, and muscle control, etc. Both excessive secretion (hyperthyroidism) and insufficient secretion (hypothyroidism) of thyroid hormones can have significant effects on various organs in our body.

There are two types of thyroid hormones: thyroxine (T4) and triiodothyronine (T3). The production of both T4 and T3 requires the element iodine. Iodine is commonly obtained through the consumption of iodized salt, so iodine deficiency is not common in Hong Kong. However, thyroid problems related to iodine deficiency are more prevalent in mountainous areas.

Thyroid hormone secretion is regulated by thyroid-stimulating hormone (TSH). Under normal circumstances, TSH is secreted by the pituitary gland and travels through the bloodstream to the thyroid. It then stimulates the TSH receptors on the surface of thyroid cells, instructing them to produce thyroid hormones T3 and T4. The secretion of thyroid hormones is tightly regulated by the body’s feedback mechanism. Any variation in thyroid hormone secretion stimulates a negative feedback response, where the pituitary gland responds in the opposite direction based on changes in the blood thyroid hormone levels. For example, if thyroid hormone secretion is excessive, the pituitary gland reduces TSH secretion, leading to a decrease in thyroid hormone production, and vice versa. This feedback mechanism helps maintain thyroid hormone secretion at normal levels. If there are issues with this feedback mechanism, it can result in thyroid dysfunction.

Hyperthyroidism (Overactive Thyroid)

The most common cause of hyperthyroidism is Graves’ disease. In Graves’ disease, the body’s immune system produces antibodies that target the TSH receptors, indirectly stimulating the secretion of thyroid hormone (T4). This uncontrolled secretion leads to an accelerated metabolism in various organs of the body, causing symptoms such as rapid heartbeat, tremors, and weight loss.

Hypothyroidism (Underactive Thyroid)

Conversely, if thyroid hormone production decreases due to certain reasons (the most common being Hashimoto’s thyroiditis or post-surgical or post-radioiodine treatment-induced hypothyroidism), the function of cells in various organs is affected, resulting in a slowed metabolism. Symptoms of hypothyroidism include slow heartbeat, loss of appetite, weight gain, and constipation. If left untreated, hypothyroidism can lead to complications such as cardiovascular diseases due to elevated levels of bad cholesterol in the blood, caused by a reduced metabolism of cholesterol by the liver.

Surgical Disease of Thyroid

Surgical disease of thyroid include thyroid cysts, thyroid nodules, and thyroid cancer. These conditions are unrelated to thyroid hormone secretion, and therefore, patients have normal thyroid hormone levels.

Patients often seek medical attention due to swelling in the neck (goiter). The doctor will arrange a thyroid ultrasound to determine the cause of the goiter. The ultrasound helps the doctor differentiate between thyroid cysts, nodules, or thyroid cancer. In some cases, the doctor may also arrange for an ultrasound-guided fine-needle aspiration, where cells are extracted from the thyroid cyst or nodule for analysis to determine the underlying cause.

Thyroid diseases are influenced by several factors, including:

1. Family history: Some thyroid diseases, such as Graves’ disease and Hashimoto’s thyroiditis, have a genetic component. According to statistics, relatives of individuals with Graves’ disease have a 9 to 20 times higher chance of developing the condition compared to individuals without a family history. Other thyroid diseases, such as multinodular goiter and thyroid cancer, also have a certain genetic correlation.
2. Iodine intake: Excessive or inadequate intake of iodine, an essential element for thyroid function, can lead to abnormal thyroid hormone secretion.
3. Pituitary gland dysfunction: The secretion of thyroid-stimulating hormone (TSH) by the pituitary gland plays a crucial role in regulating thyroid hormone production. Imbalances in pituitary function can affect thyroid hormone levels.
4. Autoimmune abnormalities: Graves’ disease is caused by an autoimmune dysfunction in which the body produces antibodies that stimulate the TSH receptors on thyroid cells, leading to excessive secretion of thyroid hormones (T4). This uncontrolled hormone production results in accelerated metabolism and the symptoms of hyperthyroidism. Other autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis, can also increase the risk of developing thyroid disorders.

The symptoms of thyroid disorders can be categorized into several main types:

Hyperthyroidism

Individuals with hyperthyroidism experience an overproduction of thyroid hormones, leading to accelerated metabolism. Symptoms may include:

• Rapid heartbeat, palpitations
• Tremors in the hands
• Sensitivity to heat
• Irritability, mood swings
• Depression
• Insomnia
• Increased appetite with significant weight loss
• Menstrual irregularities
• Diarrhea, frequent bowel movements

Hypothyroidism

On the contrary, individuals with hypothyroidism have an underactive thyroid gland, resulting in slow metabolism. Common symptoms include:

• Slow heart rate
• Sensitivity to cold
• Decreased body temperature
• Depression
• Significant weight gain
• Menstrual changes, including cessation of periods
• Constipation

Goiter (Enlarged Thyroid)

A goiter refers to the swelling of the thyroid gland located in the front of the neck.

Common causes include Graves’ disease, multinodular goiter, solitary thyroid nodule, thyroid cysts, and thyroid cancer.

The clinical symptoms of goiter may vary depending on the underlying cause. For example, a goiter caused by Graves’ disease typically appears as a symmetrical swelling, while a goiter caused by a solitary thyroid nodule may result in asymmetrical enlargement. Detailed clinical examinations and, in some cases, thyroid ultrasound can help differentiate the specific cause.

Proptosis (Bulging Eyes)

Patients with Graves’ disease may experience proptosis, also known as bulging eyes. This condition occurs due to the immune system producing antibodies that attack the eye muscles, affecting their contraction and causing the eyes to protrude.

However, some individuals with thyroid disorders may not exhibit obvious symptoms, particularly in the early stages of the disease. Therefore, it is recommended to seek medical attention as early as possible if there are suspicions of a thyroid disorder.

Blood Tests: Thyroid Function Tests

Thyroid function tests involve evaluating the secretion of thyroid hormones within the body and can be determined through blood tests. Thyroid function tests typically include measuring the levels of triiodothyronine (T3), thyroxine (T4), and thyroid-stimulating hormone (TSH). These tests help doctors differentiate between hyperthyroidism, hypothyroidism, or normal thyroid function.

For the diagnosis of thyroid nodules, doctors generally arrange the following three tests:

Clinical Examination

Through physical examination and clinical assessment, doctors can inquire about the patient’s medical history, family history, and relevant symptoms. Clinical palpation allows doctors to determine the presence of thyroid enlargement, assess the symmetry and uniformity of the enlargement, check for other palpable masses or lymph node swelling in the neck, and evaluate any compression on the trachea. After the initial evaluation, doctors may arrange further examinations such as thyroid ultrasound or fine-needle aspiration for a more detailed assessment.

Thyroid Ultrasound

Thyroid ultrasound is a non-invasive examination. During the procedure, the doctor applies gel to the patient’s neck and uses an ultrasound probe to obtain real-time images of the thyroid gland. The doctor captures corresponding images during the examination for evaluation. Thyroid ultrasound helps assess the size of the thyroid gland, the size and nature of any thyroid lesions, blood flow around the lesions, identification of calcifications, differentiation of thyroid cysts and nodules, and evaluation of lymph node enlargement in the neck, among other aspects.

Pathological Examination

Following evaluation, doctors may require a pathological report to provide further diagnostic information. The most commonly used method is ultrasound-guided fine-needle aspiration. During the procedure, the doctor uses ultrasound to locate the lesion and then extracts a small amount of cells from the lesion using a fine needle (typically 21 or 23-gauge). The patient may experience mild discomfort, and the procedure only leaves a single needle puncture wound. The extracted cells are sent to the pathology department for analysis. Pathologists observe the characteristics of the cells under a microscope, identify the cell types, and pay particular attention to any features indicative of cancer cells. All examination findings are documented in the pathology report. In addition to recommending fine-needle aspiration for thyroid lesion sampling, doctors may also suggest fine-needle aspiration of enlarged neck lymph nodes for analysis, if necessary.

After clinical examination, thyroid ultrasound, and pathological examination, doctors can generally make a diagnosis, determine the nature of the thyroid nodule, and develop a treatment plan for the patient.

Other Tests

Additional tests such as computerized scanning, chest X-rays, and electrocardiograms may be performed depending on the specific clinical situation.

Different thyroid disorders require different treatment approaches. Doctors should make an accurate diagnosis through detailed clinical examinations, imaging tests, and pathological analysis before formulating the appropriate treatment plan.

Medication Therapy

Medication is the primary method for treating functional thyroid diseases such as hyperthyroidism or hypothyroidism. To treat Graves’ disease or hyperthyroidism, doctors mainly prescribe antithyroid medications. These medications work by suppressing thyroid hormone secretion and function, allowing the patient’s thyroid secretion and metabolism to return to normal. Commonly used medications include carbimazole and propylthiouracil.

Patients need close monitoring of their thyroid hormone levels when starting medication and until the medication dosage is adjusted to maintain normal thyroid hormone levels. Patients typically need to take medication for at least one and a half to two years until their thyroid function returns to normal before discontinuing the medication. About 50% of people can achieve remission after discontinuing medication, but some patients may experience relapses or recurring conditions. Some patients may develop allergic reactions to the medication, such as itching or skin rashes. Other possible complications include temporary liver function impairment, requiring a switch to other types of medication or alternative treatment methods.

For hypothyroidism, doctors prescribe appropriate thyroid hormone replacement supplements to balance thyroid hormone levels. They also identify the underlying causes and treat them accordingly. Doctors may adjust the medication dosage based on blood tests to monitor the patient’s thyroid hormone secretion.

Surgical Removal (Thyroidectomy)

When a patient’s goiter affects external appearance, the thyroid nodules are excessively large or compress the trachea, there are suspicions of cancer based on examination reports, or Graves’ disease is recurrent or uncontrolled, doctors may recommend thyroidectomy (surgical removal of the thyroid). Thyroidectomy can be performed as total thyroidectomy or hemithyroidectomy, both requiring general anesthesia. After administering anesthesia, doctors make an incision in the patient’s neck, typically concealed within natural neck creases to minimize postoperative scarring. Total thyroidectomy involves removing the entire thyroid gland and is performed for conditions such as Graves’ disease, multiple thyroid nodules, or thyroid cancer. Since the thyroid is the only organ in our body that produces thyroid hormones, patients need to take daily thyroid hormone replacement supplements to maintain thyroid levels. The total thyroidectomy procedure typically takes about 2 hours. On the other hand, hemithyroidectomy involves removing the affected side of the thyroid gland while preserving the other side. As the remaining thyroid can adequately compensate for the overall thyroid function, patients do not need to take medication after surgery. Hemithyroidectomy usually takes about 1.5 hours.

Radioactive Iodine Therapy

Radioactive iodine therapy is used primarily to treat hyperthyroidism by using a radioactive iodine solution. Since the thyroid naturally absorbs and concentrates iodine, the administered radioactive iodine concentrates in the thyroid, releasing radiation to kill some thyroid cells and reduce thyroid hormone production and secretion. Patients typically require one to three doses of radioactive iodine to resolve hyperthyroidism. This treatment method is cost-effective and convenient, but it is not suitable for pregnant women and patients with eye diseases.

Radiofrequency Ablation

Radiofrequency ablation (RFA) is a relatively new method for treating thyroid nodules using radiofrequency energy. During the treatment, doctors first inject a small amount of local anesthesia into the skin and then use ultrasound guidance to insert a radiofrequency needle into the nodule. The high-energy radiofrequency burns the nodule tissue, causing necrosis, which is subsequently absorbed by the body. The entire treatment process takes only a few minutes, and the advantage of this procedure is that it does not leave visible scars on the skin, resulting in better aesthetics compared to traditional surgery.