Hyperthyroidism

Gastroenterology (12%) Core Clinical Conditions

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Definition Aetiology Pathophysiology Sign and Symptoms Investigations Management

Hyperthyroidism is a medical condition characterised by the overproduction of thyroid hormones, resulting in an accelerated metabolic rate. The thyroid gland, located in the front of the neck, is responsible for producing and releasing hormones that control various bodily functions. This condition occurs when the thyroid gland becomes excessively active, producing an excess amount of thyroid hormones, primarily triiodothyronine (T3) and thyroxine (T4). As a result, the body's metabolism increases, causing a range of symptoms and potential complications.

1. Graves' Disease: Graves' disease is the most common cause of hyperthyroidism. It is an autoimmune disorder in which the body's immune system mistakenly attacks the thyroid gland, leading to excessive production of thyroid hormone. The reason behind this autoimmune response is not entirely understood, but it is believed to involve a combination of genetic and environmental factors.

2. Thyroid Nodules: The presence of nodules or small growths on the thyroid gland can also result in hyperthyroidism. These nodules can be either benign or cancerous. When a nodule becomes overactive and starts producing excess thyroid hormone, it can lead to hyperthyroidism.

3. Excessive Iodine Intake: Iodine is an essential nutrient required for the production of thyroid hormone. While iodine deficiency can cause hypothyroidism, excessive iodine intake can trigger hyperthyroidism. This is particularly relevant in cases where individuals consume large amounts of iodine-rich foods or supplements.

4. Thyroiditis: Thyroiditis is the inflammation of the thyroid gland, which can be caused by several factors such as viral or bacterial infections, certain medications, or an autoimmune condition. In some cases, thyroiditis can cause a transient phase of hyperthyroidism due to the release of stored thyroid hormone from the damaged gland.

5. Pituitary or Hypothalamic Tumours: Although relatively rare, tumours in the pituitary gland or hypothalamus can disrupt the normal functioning of the thyroid gland. These tumours can produce excess thyroid-stimulating hormone (TSH), leading to increased production of thyroid hormone and subsequent hyperthyroidism.

6. Medications: Certain medications, such as amiodarone (used for heart irregularities), lithium (used for bipolar disorder), and interferon-alpha (used to treat certain cancers and viral infections), can interfere with thyroid function and cause hyperthyroidism as a side effect.

Thyroid Hormone Regulation:

To comprehend the pathophysiology of hyperthyroidism, it is essential to first understand the regulation of thyroid hormone synthesis and secretion. The hypothalamus-pituitary-thyroid (HPT) axis plays a key role in this process. The hypothalamus secretes thyrotropin-releasing hormone (TRH) which stimulates the anterior pituitary gland to release thyroid-stimulating hormone (TSH). TSH then acts on the thyroid gland, stimulating it to produce and release thyroxine (T4) and triiodothyronine (T3) hormones.

Causes of Hyperthyroidism:

Hyperthyroidism can arise due to various etiologies, the most common being Graves' disease, an autoimmune disorder. In Graves' disease, autoantibodies known as thyroid-stimulating immunoglobulins (TSI) bind to the TSH receptor on thyroid follicular cells, mimicking the action of TSH. This leads to the continuous stimulation of the thyroid gland, resulting in excessive production and release of thyroid hormones.

Other causes include toxic multinodular goitre, where multiple nodules within the thyroid gland produce excess thyroid hormones independently of TSH stimulation. Thyroiditis, which causes inflammation of the thyroid gland, can also trigger hyperthyroidism due to leakage of stored thyroid hormones into the bloodstream.

Altered Physiology:

The excessive production and release of thyroid hormones in hyperthyroidism result in diverse physiological and metabolic effects. Thyroid hormones play a crucial role in modulating the basal metabolic rate (BMR) of cells throughout the body. Consequently, an increase in thyroid hormone levels leads to an upregulation of metabolic processes in various organs and tissues.

This increased metabolic activity may result in weight loss, increased appetite, and elevated heat production, leading to heat intolerance and excessive sweating. Patients with hyperthyroidism commonly experience symptoms such as palpitations, tremors, and nervousness due to enhanced sympathetic nervous system activation. Moreover, thyroid hormones have a profound effect on the cardiovascular system. They increase heart rate, cardiac contractility, and peripheral vascular resistance, leading to hypertension and an increased risk of cardiac arrhythmias. Additionally, hyperthyroidism can result in a hypercoagulable state, increasing the risk of thromboembolic events.

1. Unexplained Weight Loss: Hyperthyroidism often leads to rapid and unexplained weight loss, even without changes in diet or physical activity. This occurs due to an increased metabolic rate caused by the excess thyroid hormones.

2. Increased Appetite: Despite weight loss, individuals with hyperthyroidism might experience an increase in appetite. The heightened metabolic activity prompts the body to demand more energy.

3. Elevated Heart Rate: A common symptom is a rapid or irregular heartbeat, also known as palpitations. The overactive thyroid gland stimulates the heart, leading to increased heart rate and even heart murmurs in severe cases.

4. Fatigue and Weakness: Paradoxically, individuals with hyperthyroidism might feel fatigued despite increased metabolism. This fatigue can be accompanied by muscle weakness and reduced stamina.

5. Nervousness and Anxiety: An overproduction of thyroid hormones can cause increased levels of anxiety, nervousness, and irritability. Patients may feel restless and find it hard to relax or concentrate on tasks.

6. Increased Sweating: Hyperthyroidism often leads to excessive sweating and an intolerance to heat. Individuals may commonly experience sweaty palms, increased body odour, and a general feeling of being overheated.

7. Changes in Bowel Habits: Hyperthyroidism can cause changes in bowel movements, with individuals experiencing more frequent and loose stools. Some may even develop diarrhoea.

8. Sleep Disturbances: Patients with hyperthyroidism often suffer from sleep disturbances such as insomnia or difficulty falling asleep. This could be attributed to the heightened levels of anxiety and restlessness.

9. Tremors: Fine tremors in the hands or fingers are a classic sign of hyperthyroidism. These tremors may be noticeable when holding objects, writing, or engaging in other fine motor activities.

10. Enlarged Thyroid: In some cases, the thyroid gland may enlarge and become visibly swollen. This condition, known as a goitre, can cause discomfort and difficulty swallowing or breathing.

As a Physician Associate, the diagnosis and investigations for hyperthyroidism involve a comprehensive approach to gather all the necessary information. Here is a list of key diagnoses and investigations commonly used in evaluating patients suspected of having hyperthyroidism:

1. History Taking: Begin by conducting a thorough medical history, including any family history of thyroid disorders, recent changes in weight or energy levels, and any associated symptoms such as palpitations, heat intolerance, or tremors.

2. Physical Examination: Perform a detailed physical examination, with special attention to signs of hyperthyroidism, such as fine tremors, smooth and warm skin, rapid heart rate, and enlarged thyroid gland (goitre).

3. Blood Tests:

• Thyroid Stimulating Hormone (TSH) Level: Measure the serum TSH level, as it is typically suppressed in hyperthyroidism. In hyperthyroidism cases, an increased production of T3 and T4 by the thyroid gland leads to high hormone levels in the blood. As a result, the pituitary gland is signalled to decrease TSH production. Therefore, low levels of TSH (<0.4 mU/L) are commonly observed in hyperthyroidism, indicating excessive thyroid hormone production.

• Free Thyroxine (T4) Level: Assess the concentrations of circulating free thyroxine, which are usually elevated in hyperthyroidism. Elevated levels of T4 (usually above the upper limit of the normal range) are an essential indicator of hyperthyroidism. Excessive production of T4 is often linked to an overactive thyroid gland, confirming the diagnosis.

• Triiodothyronine (T3) Level: Measuring the T3 hormone levels can help confirm the diagnosis and differentiate between different types of hyperthyroidism. Similar to T4, high levels of T3 (above the normal range) can indicate hyperthyroidism. The presence of elevated T3 levels, along with increased T4, serves as a valuable confirmation of the diagnosis.

• Thyroid Antibodies: Test for the presence of thyroid autoantibodies, such as thyroid peroxidase antibodies (TPOAb), to help determine the underlying cause of hyperthyroidism, such as Graves' disease or Hashimoto's thyroiditis.

• Typically, low TSH levels and high T4 and T3 levels are indicative of an overactive thyroid gland.

4. Thyroid Ultrasound: an ultrasound scan of the thyroid gland can provide valuable insights, especially in cases of goitre or suspected nodules, helping to assess the size, shape, and structure of the thyroid gland.

6. Fine Needle Aspiration (FNA) Biopsy: If any thyroid nodules are found during the ultrasound, an FNA biopsy may be performed to assess if the nodule is benign or malignant.

Treatment Options:

You refer the patient urgently to endocrinology.

However, the choice of treatment will depend on factors such as the severity of hyperthyroidism, the underlying cause, the patient's age, comorbidities, and patient preferences. Common treatment options include:
a. Antithyroid Medications: The use of thionamide drugs, such as carbimazole or Propylthiouracil, helps inhibit thyroid hormone synthesis. Monitor patients closely for potential side effects such as agranulocytosis or hepatotoxicity.
b. Beta-Blockers: These medications help alleviate symptoms such as palpitations, tremors, and anxiety associated with hyperthyroidism. Propranolol is commonly used, but select it cautiously in patients with asthma or heart failure.
c. Radioactive Iodine Therapy: This treatment involves administering a radioactive iodine capsule or liquid, leading to destruction of thyroid tissue and subsequent reduction in hormone production. Collaborate with endocrinology specialists to determine the appropriate therapy and follow-up care.
d. Surgery: In some cases, patients may require surgical intervention to remove all or part of the thyroid gland (thyroidectomy). Postoperative care includes monitoring for complications, providing appropriate analgesia, and thyroid hormone replacement therapy, if necessary.

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