Subacute Thyroiditis - Causes, Symptoms, Diagnosis, and Management

Introduction

Subacute thyroiditis is a type of thyroiditis in which there is swelling and pain in the thyroid gland. The clinical symptoms of the condition result from either the initial release of the thyroid hormones from the inflamed tissues during the thyrotoxicosis phase or a lack of the thyroid hormones during the hypothyroid phase. The condition is more prevalent in women as compared to men. In addition, the condition often occurs after an upper respiratory tract infection or sore throat. This is why the condition is considered to be triggered by some kind of viral infection. The rate of incidence of the condition is 12.1 cases per 1,00,000 per year. Subacute thyroiditis is more common in youth and middle age, and the frequency decreases in old age.

What Is a Thyroid Gland?

The thyroid gland is an endocrine gland, shaped like a butterfly, and present in front of the neck. The thyroid consists of two lobes and these lobes are linked by a band of tissues known as the isthmus. Both lobes are beneath the voice box on either side of the windpipe (trachea). The main function of the thyroid gland is the production of thyroid hormones. These hormones are crucial for growth, development, and metabolism. The thyroid hormones are thyroxine (T4), triiodothyronine (T3), and calcitonin. These hormones are vital for body functions, and an imbalance in their level can cause multiple problems like hypothyroidism, hyperthyroidism, thyroid nodules, Graves’ disease, Hashimoto’s disease, thyroiditis, etc

What Is Thyroiditis?

Thyroiditis is defined as the inflammation (swelling) of the thyroid gland, which can cause hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid). Thyroiditis can be caused by the body's autoimmune reaction (some patients generate anti-thyroid antibodies), viral infections, or medication side effects. The clinical course of thyroiditis is determined by its type. However, there are three phases of thyroiditis:

1. Thyrotoxic Phase: The thyroid glands swell and release too much thyroid hormone during this phase.

2. Hypothyroid Phase: Following a few weeks of over secretion of thyroid hormone in the thyrotoxic phase, the thyroid gland will no longer have any thyroid hormone left to release during this phase. As a result, a hypothyroidism phase will develop.

3. Euthyroid Phase: This phase may come temporarily before the hypothyroid phase. However, this phase usually occurs after the thyroid gland has healed from inflammation and can maintain normal thyroid hormone levels.

What Are the Different Types of Thyroiditis?

A. Hashimoto’s Thyroiditis: It is an autoimmune condition that occurs due to the action of anti-thyroid antibodies. Symptoms like hypothyroidism and in rare cases, thyrotoxicosis occur. They are diagnosed by undergoing thyroid function test and thyroid antibody test. Hypothyroidism is permanent in this condition.

B. Subacute Thyroiditis: It is caused by viral infection. Pain, thyrotoxicosis followed by hypothyroidism are the common symptoms. Thyroid function test, radioiodine uptake, and sedimentation rate test are done for diagnosing the condition. In rare cases, hypothyroidism can persist permanently. Otherwise, normal thyroid function may resolve in 12 to 18 months.

C. Silent Thyroiditis: It is an autoimmune condition that occurs due to anti-thyroid antibodies. Painless, thyrotoxicosis followed by hypothyroidism are the most common symptoms. They are diagnosed by performing thyroid function test, thyroid antibody test, and radioiodine uptake test. There is a 20 % chance of developing permanent hypothyroidism. However, normal thyroid function may resolve in 12 to 18 months.

D. Postpartum Thyroiditis: It is an autoimmune condition that occurs due to anti-thyroid antibodies. Symptoms include thyrotoxicosis followed by hypothyroidism. Thyroid function test and thyroid antibody test are the diagnostic tests.

E. Drug-Induced Thyroiditis: Effect of certain drugs like; Amiodarone, Lithium, Interferon, Cytokines, etc cause drug-induced thyroiditis. Symptoms can be hypothyroidism or hyperthyroidism. Thyroid function test and thyroid antibody test are recommended for diagnosing the condition. The condition persists until the usage of a specific drug is discontinued.

F. Radiation-Induced Thyroiditis: They are caused by radiation exposure or treatment with radioactive iodine. The symptoms that appear are hypothyroidism but in rare cases, hyperthyroidism and thyrotoxicosis also occur. They are diagnosed by performing a thyroid function test. This condition results in permanent hypothyroidism.

G. Acute Thyroiditis: They are caused by bacterial infection or due to any other infectious organism. Symptoms like a painful thyroid gland, generalized illness, mild hypothyroidism develop. Thyroid function test, radioactive iodine uptake, and fine-needle aspiration biopsy are done to rule out the condition. The condition resolves after treatment of the infection.

What Is Subacute Thyroiditis?

Subacute thyroiditis is the inflammation or swelling of the thyroid gland, with pain and discomfort in the gland. It is a rare type of thyroiditis occurring due to some kind of viral infection. Subacute thyroiditis can also occur due to an autoimmune reaction of the body (the body’s immune system starts attacking its healthy cells) that follows an upper respiratory tract infection. In the case of subacute thyroiditis, the patient initially develops symptoms of hyperthyroidism or thyrotoxicosis, followed by symptoms of hypothyroidism. In rare cases, temporary vocal cord paresis (muscular weakness caused by nerve damage) may occur.

What Are the Other Names for Subacute Thyroiditis?

The other names for subacute thyroiditis are:

• De Quervain’s thyroiditis.

• Subacute non-suppurative thyroiditis.

• Giant cell thyroiditis.

• Subacute granulomatous thyroiditis.

What Causes Subacute Thyroiditis?

Subacute thyroiditis is often associated with viral infection because of the tendency of the condition to develop after an upper respiratory tract infection or sore throat, infection of the ears, sinus, and common cold. Additionally, this condition can occur as a result of the autoimmune response of the body.

What Are the Common Signs and Symptoms of Subacute Thyroiditis?

The symptoms of subacute thyroiditis include:

• Swelling in the thyroid gland.

• Pain in the thyroid gland.

• Radiating pain to jaws and ears.

• Tiredness and fatigue.

• Hoarseness of voice.

• Difficulty in swallowing.

• Pain in muscles and pain in joints.

Swelling in the thyroid gland can cause excessive hormone secretion, leading to hyperthyroidism. Therefore, symptoms of subacute thyroiditis due to hyperthyroidism are:

• Irritability and restlessness.

• Anxiety.

• Heat intolerance.

• Increased bowel movement may cause diarrhea.

• Unusual hair loss.

• Altered mood.

• Shakiness and tremors.

• Excessive sweating.

• Unusual weight loss (with normal appetite).

• Palpitations.

• Irregular menstrual cycles in women.

Symptoms of subacute thyroiditis due to hypothyroidism are:

• Fatigue.

• Intolerance towards cold.

• Unusual weight gain.

• Depression.

• Irregular and heavy menstrual cycles.

• Constipation.

• Mood changes.

• Dryness of skin.

What Are the Types of Subacute Thyroiditis?

Subacute thyroiditis is of the following four types:

1. Subacute Granulomatous Thyroiditis: This is the most common subacute thyroiditis due to viral infections.

2. Postpartum Thyroiditis: This type of subacute thyroiditis occurs within one year after giving birth, and it usually subsides after 18 months. The condition starts with hyperthyroidism and then progresses to hypothyroidism.

3. Subacute Lymphocytic Thyroiditis: This type of subacute thyroiditis also occurs during the postpartum period (after childbirth). The symptoms of hyperthyroidism occur within three months after childbirth, whereas symptoms of hypothyroidism can last for a few months.

4. Palpation Thyroiditis: This type of subacute thyroiditis occurs when there is repeated examination of the thyroid gland (known as palpation), resulting in damaged thyroid follicles.

How Are Subacute Thyroiditis Diagnosed?

The diagnosis of subacute thyroiditis is made with the help of physical examination, clinical signs and symptoms, and several laboratories and image testing.

• Blood examinations are done to check the levels of thyroid-stimulating hormone (TSH), thyroxine(T4), triiodothyronine (T3), and free T4 are checked. In addition, thyroglobulin levels and C-reactive protein are also checked.

• Radioactive iodine uptake and thyroid scintigraphy may also be done to confirm the diagnosis. This test uses radioactive iodine, and the scan will show localized radioactive iodine uptake by the nodules and decreased uptake by the thyroid tissues in the background.

• Erythrocyte sedimentation rate (ESR) is done to determine any type of inflammatory activity in the body. ESR is high in the case of subacute thyroiditis.

How Are Subacute Thyroiditis Treated?

The treatment of subacute thyroiditis includes:

• In some patients who do not have significant symptoms, no treatment is required and the condition gets better on its own.

• In the presence of mild symptoms, non-steroidal anti-inflammatory drugs (NSAIDs) to reduce pain and inflammation may be prescribed. For example, Acetaminophen is useful in reducing pain and inflammation in the case of subacute thyroiditis.

• When NSAIDs fail to provide symptomatic relief, corticosteroids like Prednisone are given. A daily dose of 20 to 40 milligrams of Prednisone is recommended. The dosage is reduced over six weeks.

• Beta-blockers are also advised to reduce blood pressure which causes palpitation in the early stages of subacute thyroiditis (palpitations and high blood pressure occur due to thyrotoxicosis).

Conclusion

Subacute thyroiditis is a rare condition characterized by swelling and often pain in the thyroid gland. However, the condition is not a life-threatening condition and can be managed. The prognosis of the disease is excellent; almost 90 percent of the people affected by subacute thyroiditis have spontaneous and complete recovery. The patients regain normal thyroid functioning. In rare cases, the patient may develop permanent hypothyroidism and require lifelong thyroid replacement therapy.