Chronic lymphocytic thyroiditis, also known as Hashimoto’s thyroiditis, is a common autoimmune condition that affects the thyroid gland. The thyroid is a small, butterfly-shaped gland at the front of the neck that makes hormones that regulate metabolism, energy levels, and many other body functions. Chronic lymphocytic thyroiditis is not a cancer.
In this condition, the immune system (the body’s defense system against infection) mistakenly attacks the thyroid gland. The result is long-term inflammation and slow, gradual damage to the thyroid. Over time, the thyroid may become less able to produce enough hormone, leading to hypothyroidism (an underactive thyroid).
Chronic lymphocytic thyroiditis is one of the most common causes of hypothyroidism. It can affect people of any age, but is most common in middle-aged women.
What are the symptoms of chronic lymphocytic thyroiditis?
Many people with chronic lymphocytic thyroiditis have no symptoms at first, and the condition is often discovered on routine blood work or imaging done for another reason.
As the thyroid gland becomes more damaged and hormone production decreases, symptoms of hypothyroidism may develop. These may include:
- Fatigue and low energy.
- Weight gain.
- Feeling unusually cold.
- Constipation.
- Dry skin.
- Depression or mood changes.
- Slowed heart rate.
- Menstrual irregularities.
- Muscle weakness or cramps.
- A puffy face or swelling in the front of the neck from an enlarged thyroid (a goiter).
Symptoms tend to develop slowly over months to years and may be mild at first, making them easy to overlook.
What causes chronic lymphocytic thyroiditis?
Chronic lymphocytic thyroiditis is an autoimmune disease. In a healthy person, the immune system defends against threats like viruses and bacteria. In autoimmune diseases, the immune system mistakenly produces antibodies (proteins that normally target infections) against the body’s own tissues. In chronic lymphocytic thyroiditis, these antibodies — called autoantibodies — target proteins in thyroid cells. This attracts immune cells to the thyroid, causing long-term inflammation and damage.
The exact reason the immune system behaves this way is not fully understood, but several risk factors have been identified:
- Family history. Having a close relative with an autoimmune disease (such as type 1 diabetes or lupus) increases the risk.
- Sex. Women are much more likely than men to develop this condition.
- Age. It is most common in middle-aged adults, especially women over 40.
- Other autoimmune conditions. Having another autoimmune disease, such as rheumatoid arthritis, type 1 diabetes, or celiac disease, increases the risk.
- Radiation exposure. Previous radiation exposure, from medical treatments or environmental sources, may increase the risk.
- Genetics. Certain inherited genes can increase the likelihood of developing autoimmune thyroid disease.
How is the diagnosis of chronic lymphocytic thyroiditis made?
The diagnosis of chronic lymphocytic thyroiditis is usually made with a combination of blood tests and, sometimes, imaging. A tissue biopsy is not needed in most cases. Blood tests used to make the diagnosis include thyroid-stimulating hormone (TSH), which is usually high in hypothyroidism, and free T4, which is often low when the thyroid is underactive. Two antibody tests are particularly helpful: thyroid peroxidase antibodies (TPOAb), which are found in the blood of most people with this condition, and thyroglobulin antibodies (TgAb), which are also commonly present. A neck ultrasound may be performed and typically shows an enlarged thyroid with an irregular, patchy appearance. A fine needle aspiration (FNA) biopsy is not routinely needed for this diagnosis; it is performed only when a thyroid nodule looks suspicious on ultrasound and cancer needs to be ruled out. When a biopsy is performed and shows features of chronic lymphocytic thyroiditis, this is usually an incidental finding alongside the main reason for the biopsy.
What does chronic lymphocytic thyroiditis look like under the microscope?
When thyroid tissue is examined under the microscope, chronic lymphocytic thyroiditis shows characteristic signs of long-term immune activity. These include:
- Lymphocytes and plasma cells. Large numbers of these immune cells are seen throughout the thyroid tissue. Their presence is the hallmark of chronic lymphocytic thyroiditis and gives the condition its name.
- Lymphoid follicles with germinal centers. The immune cells form organized clusters that look very similar to those normally found in lymph nodes. Their presence in the thyroid indicates that the immune attack has been going on for some time.
- Oncocytic (Hürthle cell) change. Some thyroid cells become larger than normal, with bright pink cytoplasm due to an increase in mitochondria (the energy factories of the cell). In the thyroid, these cells are called Hürthle cells. This change is a response to chronic inflammation and is not cancer.
- Loss of normal follicles. The small round structures (follicles) that normally store thyroid hormone become smaller and fewer in number as thyroid tissue is gradually replaced by immune cells and scar tissue.
- Mild cell changes. Some thyroid cells may appear slightly abnormal due to the long-standing inflammation. These changes are not cancer but can sometimes be mistaken for cancer on small samples, which is why correlation with the clinical picture is important.
Chronic lymphocytic thyroiditis and thyroid cancer
Chronic lymphocytic thyroiditis is a benign (noncancerous) condition and does not usually turn into cancer. However, a few important points are worth knowing:
- Coexistence with papillary thyroid carcinoma. Papillary thyroid carcinoma, the most common type of thyroid cancer, is sometimes found in a thyroid that also shows chronic lymphocytic thyroiditis. This does not mean the thyroiditis caused the cancer — many researchers believe the two conditions simply occur together more often than expected by chance. When they coexist, the cancer is usually found at an early stage and has a very good outcome.
- Small increased risk of thyroid lymphoma. Long-standing chronic lymphocytic thyroiditis can, in rare cases, lead to the development of a lymphoma within the thyroid gland. A lymphoma is a cancer that starts in lymphocytes, the type of immune cell that normally helps the body fight infection. The type that most often arises in this setting is called extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma), a slow-growing lymphoma that tends to stay confined to the organ where it started. The overall risk remains low, but any rapid growth of the thyroid gland in a person with long-standing thyroiditis should be evaluated promptly.
These associations do not mean that everyone with chronic lymphocytic thyroiditis needs special cancer screening. In most cases, standard monitoring with a physical exam and blood tests is sufficient.
What happens after the diagnosis?
Treatment depends on how well the thyroid is functioning.
- Normal thyroid function. If thyroid hormone levels are normal, no medication is needed. Your doctor may recommend periodic monitoring with blood tests to check for the development of hypothyroidism over time.
- Hypothyroidism. If the thyroid is underactive, levothyroxine (a synthetic form of thyroid hormone) is prescribed to replace what the thyroid can no longer make. The dose is adjusted based on blood tests. Most people do very well on this treatment and have few or no symptoms once the dose is right.
- Goiter causing symptoms. If the thyroid becomes very enlarged and causes trouble swallowing, breathing, or a noticeable neck mass, surgery may be considered. This is uncommon in chronic lymphocytic thyroiditis.
- Pregnancy. Thyroid hormone needs increase during pregnancy. Women with chronic lymphocytic thyroiditis who are planning pregnancy or are pregnant should have their thyroid function checked regularly, as thyroid hormone doses often need to be increased.
Because chronic lymphocytic thyroiditis is associated with other autoimmune conditions, your doctor may also check for signs of related diseases if symptoms develop.
Questions to ask your doctor
- What are my thyroid hormone (TSH and free T4) levels, and what do they mean for me?
- Do I have thyroid antibodies (TPOAb or TgAb)?
- Do I need to start thyroid hormone replacement medication?
- How often should I have my thyroid function tested?
- Should I be checked for other autoimmune conditions?
- Do I need to have a neck ultrasound?
- Is there anything I should watch for that would prompt further evaluation, such as a rapidly growing lump in my neck?
- If I am planning a pregnancy, how will my thyroid be monitored during pregnancy?
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