The thyroid is a small, butterfly-shaped gland at the base of the neck that produces hormones to regulate the body’s metabolism. Autoimmune Thyroid Disease (AITD) occurs when the body’s immune system, which normally defends against foreign invaders, mistakenly attacks its own healthy thyroid tissue. This is the most common organ-specific autoimmune disorder and is more prevalent in women. The immune system’s assault can cause inflammation and damage, disrupting the thyroid’s ability to produce the correct amount of hormones. This interference can either impair the gland’s function, causing hypothyroidism (too little hormone), or stimulate it, causing hyperthyroidism (too much hormone).
The Two Primary Forms of AITD
Autoimmune thyroid diseases primarily manifest in two opposing forms: Hashimoto’s thyroiditis and Graves’ disease. Both conditions involve the immune system generating autoantibodies, which are antibodies that incorrectly target the body’s own proteins. The specific nature of this autoimmune response determines whether the thyroid becomes underactive or overactive.
Hashimoto’s thyroiditis is the most common cause of hypothyroidism, or an underactive thyroid. In this condition, the immune system gradually destroys the thyroid’s hormone-producing cells. This slow destruction leads to a progressive decline in the thyroid’s ability to produce hormones, ultimately resulting in hypothyroidism. The gland itself may initially enlarge, forming a goiter, but can shrink over many years as the tissue is damaged.
Graves’ disease is the most common cause of hyperthyroidism, or an overactive thyroid. The autoimmune attack in Graves’ disease stimulates the thyroid gland. The immune system produces antibodies known as thyrotropin receptor antibodies (TRAb) that mimic Thyroid-Stimulating Hormone (TSH). These antibodies bind to receptors on the thyroid cells, causing the gland to continuously produce and release excessive amounts of thyroid hormones.
Recognizing the Symptoms
The symptoms of AITD vary widely depending on whether the condition leads to an underactive or overactive thyroid. The onset can be gradual, and because thyroid hormones affect nearly every organ system, the symptoms can be diverse.
With Hashimoto’s thyroiditis and the resulting hypothyroidism, the body’s functions slow down. Individuals often experience persistent fatigue, sluggishness, and an increased sensitivity to cold. Unexplained weight gain, constipation, and dry, thinning hair are also common. Many people report muscle aches, joint pain, a slowed heart rate, and mood changes like depression or memory problems.
Conversely, Graves’ disease and hyperthyroidism speed up the body’s metabolic processes. This can cause anxiety, nervousness, and irritability, along with difficulty sleeping. Sufferers may experience unintentional weight loss despite an increased appetite, a rapid or irregular heartbeat, and hand tremors. A poor tolerance for heat and increased perspiration are also characteristic.
A specific symptom unique to Graves’ disease is Graves’ ophthalmopathy, or thyroid eye disease, which affects about a quarter of patients. This condition is caused by inflammation and swelling of the tissues and muscles behind the eyes. It can result in bulging eyes, a feeling of grittiness, sensitivity to light, and double vision. The eyelids may also become red, swollen, or retracted, creating a staring appearance.
The Diagnostic Process
Diagnosing an autoimmune thyroid disease begins with a review of a patient’s symptoms and medical history, followed by a physical examination. A healthcare provider will check the thyroid gland for enlargement, known as a goiter, or for any nodules. To confirm a diagnosis and identify the specific type of AITD, a series of blood tests is necessary.
Blood tests measure the levels of hormones that regulate and are produced by the thyroid. The first test is for Thyroid-Stimulating Hormone (TSH), which is produced by the pituitary gland to regulate the thyroid. Levels of the thyroid hormones themselves, thyroxine (T4) and triiodothyronine (T3), are also measured. In hypothyroidism, TSH levels are high while T4 levels are low; in hyperthyroidism, TSH is low and T4 and T3 levels are high.
To determine if the thyroid dysfunction is caused by an autoimmune process, specific antibody tests are performed. The presence of Thyroid Peroxidase Antibodies (TPOAb) is a strong indicator of Hashimoto’s thyroiditis. For Graves’ disease, the marker is the TSH Receptor Antibody (TRAb), which is the antibody responsible for stimulating the thyroid gland.
In some cases, a doctor may order an imaging test to view the thyroid’s structure. A thyroid ultrasound uses sound waves to create a picture of the gland, revealing its size, shape, and any nodules. A radioactive iodine uptake scan can help differentiate causes of hyperthyroidism by measuring how much iodine the thyroid absorbs, as high uptake is characteristic of Graves’ disease.
Managing Autoimmune Thyroid Conditions
Once a diagnosis of AITD is confirmed, management focuses on correcting the hormonal imbalance and alleviating symptoms. Treatment approaches differ depending on whether the patient has hypothyroidism or hyperthyroidism. The goal is to restore normal hormone levels, a state known as euthyroid, and requires ongoing monitoring.
For hypothyroidism caused by Hashimoto’s thyroiditis, the standard treatment is thyroid hormone replacement therapy. This involves taking a daily oral medication called levothyroxine, a synthetic form of the T4 hormone. The dosage is carefully adjusted based on regular blood tests that monitor TSH levels to restore them to the normal range. For most people, this is a lifelong treatment.
Managing hyperthyroidism from Graves’ disease offers several pathways. One approach is the use of anti-thyroid medications, such as methimazole, which reduce the thyroid’s production of hormones. Another option is radioactive iodine (RAI) therapy, where a dose of radioactive iodine destroys overactive thyroid cells. Many patients who undergo RAI therapy will eventually develop hypothyroidism and require levothyroxine replacement.
In certain situations, such as when a goiter is very large or if other treatments are not suitable, surgery may be recommended. A thyroidectomy involves the surgical removal of all or part of the thyroid gland. This permanently resolves the hyperthyroidism, but the patient will need lifelong thyroid hormone replacement medication.