Thyroid Disorders: Types, Causes, and Treatments

Like a house's thermostat that controls the temperature, the thyroid helps regulate the body's metabolism, energy, and hormone balance, contributing to overall well-being. The thyroid is a butterfly-shaped organ located in the neck. It plays a role in metabolic processes and produces hormones necessary for maintaining general health.

Thyroid disorders affect about 20 million or 5% of people in the United States. This article aims to educate readers about the different types of thyroid disorders, their causes, and management options.

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Understanding the Thyroid Gland

The thyroid gland supports various functions of the body, including metabolism, heart function, digestion, and mood. It does this by releasing hormones, primarily thyroxine (T4) and triiodothyronine (T3), which influence metabolism, heart function, digestion, and mood:

• Metabolic rate: Thyroid hormones may help increase the body's basal metabolic rate, or the energy used at rest, impacting overall energy levels and body weight.
• Cardiovascular function: Thyroid hormones help support heart rate and maintain the strength of the heart muscle. A disruption in thyroid hormone balance can contribute to irregular heartbeats (arrhythmias) and other cardiovascular issues.
• Digestion: The thyroid influences digestion by regulating the release of digestive fluids and the movement of food through the gastrointestinal tract. Thyroid hormones also affect the speed of digestion, impacting nutrient absorption.
• Mood: Thyroid hormones can influence the levels of neurotransmitters in the brain (e.g., serotonin and dopamine), which regulate mood, emotions, and cognitive function. An imbalance in thyroid hormones may contribute to mood changes such as depression and anxiety.

Thyroid Hormones 

The thyroid gland produces hormones, including T4 and T3, which support various functions of the body. These hormones are made from tyrosine, an amino acid, and iodine, a mineral.  

• T4 is the most abundant hormone produced by the thyroid. It is converted to T3, the active form, in the liver, kidneys, muscles, thyroid, pituitary gland, fat cells, and brain. T4 is less biologically active than T3 but is essential for maintaining a supply of active thyroid hormones.
• T3, the biologically active thyroid hormone, impacts almost every cell in the body. It plays a key role in muscle control, brain function and development, and heart and digestive functions. This is important for sustaining body temperature and weight and ensuring adequate energy levels. 
• The C-cells in the thyroid produce a hormone called calcitonin, which helps regulate calcium in the body.

Thyroid hormones are regulated by a feedback loop involving the hypothalamus, pituitary gland, thyroid gland, and select hormones. The feedback loop helps the body to maintain a steady amount of hormones:

1. When blood thyroid hormone levels are low, the hypothalamus releases thyrotropin-releasing hormone (TRH).
2. TRH stimulates the release of thyroid-stimulating hormone (TSH) from the pituitary gland into the blood.  
3. TSH then causes the thyroid gland to produce and release primarily T4 (80%) and some T3 (20%). Once T4 and T3 levels in the blood reach a certain level, they signal the hypothalamus and pituitary gland to reduce TRH and TSH production, respectively.

Types of Thyroid Disorders

Several specific thyroid disorders are possible:

Hypothyroidism 

‍Hypothyroidism occurs when the thyroid does not produce sufficient thyroid hormone to meet the body's needs. This can lead to a slower metabolism and symptoms such as: 

• Fatigue
• Weight gain
• Cold intolerance
• Dry skin
• Hair loss
• Constipation

Hypothyroidism can also contribute to feelings of depression, poor memory, and muscle weakness. When the thyroid levels become extremely low, this can lead to myxedema. Myxedema can result in serious conditions such as very low body temperature, confusion, and heart issues.

A common cause of hypothyroidism is Hashimoto's thyroiditis, an autoimmune condition in which the body's immune system targets the thyroid gland, causing inflammation and damage. Symptoms may include fatigue, weight gain, and cold intolerance. 

Hashimoto’s occurs more commonly in women than men, most often between 30 and 50 years of age, and tends to run in families. It develops gradually over the years, with symptoms slowly progressing and potentially leading to complications if not managed.

Hyperthyroidism 

‍Hyperthyroidism is characterized by an overactive thyroid gland, resulting in a variety of symptoms:

• Weight loss
• Increased appetite
• Anxiety
• Irritability
• Tremors
• Fast heart rate (tachycardia)
• Excessive sweating
• Heat intolerance
• Fatigue

In some people, hyperthyroidism can cause exophthalmos (bulging eyes) and skin changes such as redness or swelling. Graves' disease, the most common cause of hyperthyroidism, is an autoimmune disorder in which the body's immune system mistakenly affects the thyroid gland, resulting in excessive release of thyroid hormones. This condition tends to run in families and occurs more commonly in women and those between 30 and 50 years old.

Other causes of hyperthyroidism include:

• Thyroid nodules (lumps in the thyroid gland), which may produce excessive thyroid hormones
• Thyroiditis (inflammation of the thyroid gland)
• Excessive iodine consumption

Goiter 

An enlargement of the thyroid gland is known as a goiter. Causes may include iodine deficiency, thyroid nodules, inflammation, or an overly active thyroid. Iodine is necessary for the synthesis of thyroid hormones. In instances of low iodine levels, the thyroid gland enlarges as it attempts to increase hormone production. When a goiter becomes very large, it can appear as a lump in the neck, resulting in pressure-related symptoms such as a feeling of fullness in the neck, coughing, difficulty swallowing or breathing, and voice changes.

Thyroiditis 

‍Thyroiditis refers to inflammation of the thyroid gland, which may be caused by a viral infection, autoimmune condition, or postpartum hormonal changes.

• Subacute thyroiditis, or De Quervain's thyroiditis, is often preceded by viral infection. Symptoms may include neck pain and tenderness, fever, fatigue, and malaise. Subacute thyroiditis can lead to transient hyperthyroidism followed by hypothyroidism before returning to baseline (normal) levels.
• Autoimmune conditions such as Hashimoto's can also result in thyroiditis.
• Postpartum thyroiditis occurs in the first year after childbirth.  It is thought to be caused by an autoimmune response triggered by hormonal changes during pregnancy. Similar to subacute thyroiditis, symptoms often include transient hyperthyroidism followed by hypothyroidism. Most cases of postpartum thyroiditis resolve spontaneously; however, some women may develop chronic hypothyroidism.  

Thyroid Cancer 

‍Thyroid cancer, the most common endocrine cancer, occurs more in women than in men and typically presents between 25 and 65 years of age. It has a favorable five-year survival rate of about 98% for papillary and follicular thyroid cancers. The most common type is papillary thyroid cancer, accounting for about 80% of cases. Follicular thyroid cancer is the second most common type, accounting for about 15% of cases. Less common types include medullary thyroid cancer and anaplastic thyroid cancer. During the early stages, a person may not have any symptoms.

Thyroid cancer may be incidentally detected during imaging tests for other conditions. Signs and symptoms of advanced thyroid cancer may include:

• A lump or swelling in the neck
• Difficulty swallowing
• Hoarseness
• Enlarged cervical lymph nodes

The Root Causes of Thyroid Disorders

Below are the various root causes that can contribute to thyroid disorders:

Autoimmune Disease 

‍Autoimmune thyroid conditions like Hashimoto's disease and Graves' disease can lead to thyroid dysfunction through various mechanisms:

• Hashimoto's thyroiditis: When the immune system mistakenly affects the thyroid gland, inflammation and damage result. Over time, the thyroid gland's ability to produce thyroid hormones may be impaired, contributing to hypothyroidism.  
• Graves' disease: The production of auto-antibodies that mimic the action of TSH causes overstimulation of the thyroid gland to produce and release excess thyroid hormones, leading to hyperthyroidism.

Iodine Levels

Iodine is an essential mineral that is required for the production of thyroid hormones. Deficiency or excess can significantly impact thyroid health.

• Iodine deficiency is the primary global cause of thyroid disorders, particularly in areas where iodine-rich foods are scarce. Without adequate iodine, the thyroid gland may not produce enough thyroid hormones, leading to hypothyroidism. Severe iodine deficiency during pregnancy may lead to cretinism, a condition characterized by significant mental and physical impairments in the fetus and infant.
• Conversely, excessive iodine intake can also affect thyroid function. High levels of iodine can prevent thyroid hormone synthesis, resulting in hypothyroidism, known as the Wolff-Chaikoff effect.

Genetic Factors

Knowledge about the genetic basis of thyroid disorders can help improve diagnosis, treatment, and management strategies. Autoimmune thyroid disorders (e.g., Hashimoto's and Graves' disease) have a strong genetic link. Specific genes, such as the HLA-DR genes, have been associated with increased susceptibility. Genetics can also impact the risk of thyroid cancer development. Mutations in the BRAF gene, for example, have been linked to increased thyroid cancer risk. These mutations can be acquired or inherited. Genetics can also impact the severity and progression of some thyroid disorders. For example, genetic variations may influence the response to thyroid hormone replacement therapy in people with hypothyroidism.

Environmental Factors 

Environmental factors that may impact thyroid health include:

• Perchlorate is a chemical found in some water and food. Perchlorate can interfere with the uptake of iodine by the thyroid gland, leading to reduced thyroid hormone production and potential thyroid dysfunction.
• Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), found in some industrial products and flame retardants, respectively, have been linked to thyroid disorders.
• Radiation exposure, especially exposure during childhood, can impact thyroid health.  Exposure to ionizing radiation, including from a nuclear accident or medical treatments, can increase the risk of thyroid cancer. Exposure to high amounts of radiation can damage and mutate thyroid cells into cancerous tumors.

Diagnosing Thyroid Disorders

Diagnosing thyroid disorders is a specific process. Here is what you need to know:

History and Physical Examination 

The workup for thyroid conditions begins with a history and physical exam, including:

• Symptoms
• Family history of thyroid disorders
• Medications
• Palpation of the neck to assess its size and shape (presence of a goiter or nodules)

Blood Tests

Comprehensive thyroid lab tests include:

• Thyroid-stimulating hormone (TSH): TSH is produced and released by the pituitary gland to stimulate thyroid hormone production. Abnormal TSH levels can indicate hypo- or hyperthyroidism.
• Free thyroxine (T4): Measures the level of free T4, which is the precursor to T3.  Low levels of T4 may indicate hypo- or hyperthyroidism.
• Free triiodothyronine (T3): Measures the level of free T3, the active form of thyroid hormone. Like T4, abnormal levels of T3 can indicate thyroid dysfunction.
• Thyroid antibody tests: Measure the level of antibodies that affect the thyroid gland, which can facilitate the diagnosis of autoimmune-based thyroid disorders such as Hashimoto's thyroiditis or Graves' disease.

Imaging Tests

• Ultrasound: The primary imaging test used to evaluate the thyroid gland, providing detailed images of its size, capsular structure, and other characteristics.
• Fine needle aspiration: During the thyroid ultrasound, a fine needle aspiration biopsy may be necessary to collect a sample of cells and determine whether they are benign or malignant.  
• Computed Tomography (CT): In some cases, a CT scan may be done to assess the thyroid gland's function and anatomical features.

Treatment Options for Thyroid Disorders

The following treatment options are available and will be recommended to individuals based on their unique history and other findings:

Medications

• Hypothyroidism: Synthetic thyroid hormone replacement therapy (e.g., levothyroxine) is the most common treatment for hypothyroidism, helping to support normal hormone levels.
• Hyperthyroidism:  Antithyroid drugs (e.g., methimazole or propylthiouracil) may be prescribed to help decrease the production of thyroid hormones in cases of hyperthyroidism.

Radioactive Iodine (RAI) 

The thyroid gland is the only organ in the human body that absorbs iodine. Radioactive iodine (RAI) selectively targets and affects thyroid cells. In cases of hyperthyroidism, RAI is used to reduce thyroid activity by affecting thyroid cells. 

In thyroid cancer, RAI therapy is used after thyroidectomy to target any remaining thyroid tissue, including cancerous cells, to minimize the risk of cancer recurrence. RAI is taken by mouth and absorbed by the thyroid cells.

Surgery

A thyroidectomy, the surgical removal of part or all of the thyroid gland, may be performed to address thyroid cancer, large goiters, or severe hyperthyroidism that is not responsive to other treatments.

Diet and Lifestyle 

Maintaining a healthy diet and lifestyle supports thyroid health. For example, incorporating rich dietary sources of iodine, including iodized salt, dairy products, seafood, seaweed, and iodine-fortified foods, can be helpful.

Living with Thyroid Disorders

Living with thyroid disorders involves managing symptoms and maintaining overall health through diet, exercise, stress management, and regular monitoring of thyroid function.

• Diet: A well-balanced diet rich in iodine, zinc, and selenium can support thyroid health. Avoiding excessive iodine intake and limiting processed foods can also be beneficial. A gluten-free diet may benefit some individuals, especially those with Hashimoto's thyroiditis or other autoimmune thyroid disorders.
• Exercise: Regular physical activity can support thyroid function, metabolism, and energy levels.
• Stress Management: Stress tends to worsen the symptoms of thyroid disorders, so stress management techniques such as yoga, meditation, or counseling may be helpful.

Monitoring and Follow-Up

Regularly monitoring thyroid function is crucial for individuals with thyroid disorders and is recommended for the elderly. Routine blood tests include thyroid hormone levels and antibodies. Based on these results, adjustments to medication dosage may be needed. Follow-up visits with health care providers are important to discuss any changes in symptoms and ensure that the management plan is effective.

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Key Takeaways

• Thyroid disorders, including hypothyroidism and hyperthyroidism, can have profound impacts on overall health and well-being.
• Thyroid disorders include hyper- or hypothyroidism, goiter, thyroiditis, and thyroid cancer. Causes include autoimmune disorders, inadequate iodine intake, environmental exposures, and genetics.
• The thyroid produces hormones as a result of a feedback loop:  TRH release (hypothalamus) → TSH release (pituitary gland) → T4 and T3 release (thyroid), T4 is converted into T3 (the biologically active form) → loops back to impact release of TRH by the hypothalamus.
• Diagnosis of thyroid disorders involves physical examination, blood tests, and imaging tests.
• Management options for thyroid disorders include medications, radioactive iodine therapy, and surgery.
• Dietary sources of iodine include dairy products, iodized salt, seafood, seaweed, and iodine-fortified foods.
• Routine thyroid function assessment through blood tests and follow-up visits with healthcare providers is necessary for effectively managing thyroid disorders.