Autoimmune Thyroiditis

What happens in autoimmune thyroiditis

The thyroid, a butterfly-shaped gland in the front of the neck, makes hormones that set the body's metabolic rate. In autoimmune thyroiditis, immune cells (lymphocytes) infiltrate the gland and antibodies target thyroid proteins, especially thyroid peroxidase (TPO) and thyroglobulin. Over months to years, thyroid cells are destroyed and replaced with scar tissue, so hormone production falls.

In some forms, damaged thyroid cells leak stored hormone first, causing a temporary overactive phase (thyrotoxicosis) before the underactive phase.

Autoimmune thyroiditis is related to Graves' disease. Both are autoimmune thyroid diseases, but in Graves' the antibodies stimulate the thyroid to make too much hormone.

Types

Symptoms

Many people have no symptoms for years and are found to have antibodies or a mildly raised TSH on a blood test. As thyroid function falls, symptoms develop slowly:

• tiredness and sluggishness
• weight gain and fluid retention
• feeling cold
• dry skin, brittle nails and hair thinning
• constipation
• muscle aches and joint stiffness
• low mood and poor concentration
• heavy or irregular periods and fertility problems
• slow heart rate
• puffy face and hoarse voice
• a goiter: a painless swelling in the front of the neck

During a temporary overactive phase (postpartum or painless thyroiditis), symptoms are the opposite: anxiety, palpitations, heat intolerance, weight loss and poor sleep.

Causes and risk factors

• Female sex, particularly middle age
• Family history of thyroid disease
• Other autoimmune conditions: type 1 diabetes, celiac disease, vitiligo, pernicious anemia, rheumatoid arthritis and Addison's disease
• Pregnancy and the postpartum period
• Down syndrome and Turner syndrome
• High iodine intake in susceptible people
• Radiation exposure to the neck
• Certain medicines, as listed above

Diagnosis

• TSH (thyroid-stimulating hormone): high when the thyroid is underactive. This is the main screening test.
• Free T4: low in overt hypothyroidism, normal in subclinical hypothyroidism.
• Anti-TPO antibodies: positive in about 90% of people with Hashimoto's. Anti-thyroglobulin antibodies are sometimes tested.
• Thyroid ultrasound: shows a characteristic patchy appearance and is used to assess nodules or a goiter.

Positive antibodies with normal TSH do not need treatment but do raise the chance of developing hypothyroidism over time, roughly 2 to 4% a year in women, so TSH is checked periodically.

Treatment

Levothyroxine

When TSH is elevated with low free T4 (overt hypothyroidism), treatment is levothyroxine, a synthetic version of the thyroid hormone T4, taken once daily.

• Take it on an empty stomach, 30 to 60 minutes before breakfast, or at bedtime well after food.
• Separate it by at least 4 hours from calcium, iron, antacids and some other medicines that block absorption.
• TSH is checked 6 to 8 weeks after starting or changing the dose, then usually once a year.

Treatment for subclinical hypothyroidism (high TSH, normal T4) depends on TSH level, symptoms, age and pregnancy plans.

During the overactive phase

The temporary thyrotoxic phase of postpartum or painless thyroiditis is usually managed with beta-blockers to ease symptoms. Antithyroid drugs are not used, because the gland is leaking hormone rather than overproducing it.

Diet and supplements

No diet cures autoimmune thyroiditis. Avoid excessive iodine supplements. A gluten-free diet helps people with coexisting celiac disease, but evidence for others is limited. Selenium may lower antibody levels in some studies, but its clinical benefit is uncertain.

Pregnancy

Women with Hashimoto's or positive TPO antibodies need closer monitoring in pregnancy. Thyroid hormone needs rise, often by 25 to 50% in early pregnancy, and untreated hypothyroidism can affect the baby's development. Women already on levothyroxine should contact their doctor as soon as pregnancy is confirmed.

Complications

• untreated hypothyroidism can raise cholesterol and contribute to heart disease
• infertility and pregnancy complications
• a large goiter can press on the windpipe or esophagus
• myxedema coma, a rare emergency from severe untreated hypothyroidism
• thyroid lymphoma, a rare cancer slightly more common in Hashimoto's

Outlook

Autoimmune thyroiditis is usually lifelong, but with correct levothyroxine dosing, people live normal, healthy lives. Most need regular blood tests and small dose adjustments over time.

Frequently asked questions

What is autoimmune thyroiditis?

Autoimmune thyroiditis is inflammation of the thyroid caused by the immune system attacking it. The most common type is Hashimoto's thyroiditis, which gradually destroys thyroid tissue and causes an underactive thyroid. Postpartum and painless thyroiditis are related, often temporary forms.

Is autoimmune thyroiditis the same as Hashimoto's?

Mostly. Hashimoto's thyroiditis is the most common form of autoimmune thyroiditis, and the terms are often used interchangeably. Autoimmune thyroiditis also includes atrophic, postpartum, painless and drug-induced forms.

What are the symptoms of autoimmune thyroiditis?

Many people have no symptoms at first. As the thyroid becomes underactive, symptoms include tiredness, weight gain, feeling cold, dry skin, hair thinning, constipation, low mood, heavy periods and sometimes a swollen neck. Some forms cause a short overactive phase first.

Do I need treatment if I have thyroid antibodies but normal thyroid levels?

Usually not. Positive TPO antibodies with normal TSH mean a higher chance of developing hypothyroidism in the future, so your doctor will check TSH periodically. Treatment may be considered if you are pregnant or planning pregnancy.

Can autoimmune thyroiditis be cured?

There is no cure for the autoimmune process, and thyroid damage is usually permanent. However, levothyroxine fully replaces the missing hormone. Postpartum and painless thyroiditis often resolve on their own within a year.