Hashimoto's Thyroiditis

What happens in Hashimoto's

The thyroid, a butterfly-shaped gland in the front of the neck, makes hormones (T4 and T3) that control metabolism, energy, heart rate and body temperature. In Hashimoto's, immune cells (lymphocytes) infiltrate the gland and antibodies target thyroid proteins, especially thyroid peroxidase (TPO). Over years, thyroid tissue is damaged and replaced by scar tissue, and hormone production falls.

The pituitary gland responds by releasing more thyroid-stimulating hormone (TSH) to push the thyroid harder. That is why a rising TSH is the earliest blood test sign. Thyroid function may stay normal for years, become mildly low (subclinical hypothyroidism), then overtly low (hypothyroidism).

Early on, inflamed thyroid cells may leak stored hormone, causing a brief overactive phase ("hashitoxicosis") with palpitations and anxiety.

Symptoms

Symptoms develop slowly and are easy to attribute to aging or stress:

• tiredness and sluggishness
• weight gain or difficulty losing weight
• feeling cold
• constipation
• dry skin, brittle nails and thinning hair, including the outer eyebrows
• puffy face and eyes
• muscle aches, stiffness and cramps
• low mood, slowed thinking and poor memory
• heavy or irregular periods
• slow heart rate
• hoarse voice
• a painless enlarged thyroid (goiter) in some people

Causes and risk factors

• female sex
• family history of thyroid or autoimmune disease
• other autoimmune conditions: type 1 diabetes, celiac disease, vitiligo, pernicious anemia, rheumatoid arthritis, Addison's disease
• age: more common with increasing age
• pregnancy: postpartum thyroiditis can unmask Hashimoto's
• high iodine intake, some medicines (amiodarone, lithium, immune checkpoint inhibitors, interferon)
• radiation exposure to the neck
• genetic conditions: Down syndrome and Turner syndrome

Diagnosis

• TSH: high in hypothyroidism.
• Free T4: low in overt hypothyroidism, normal in subclinical hypothyroidism.
• Anti-TPO antibodies: positive in about 9 in 10 people with Hashimoto's. Anti-thyroglobulin antibodies are sometimes tested.
• Thyroid ultrasound: shows a characteristic patchy, coarse texture and checks any nodules.

Positive antibodies with normal thyroid function mean a higher risk of developing hypothyroidism later; yearly TSH checks are reasonable.

Hashimoto's vs hypothyroidism

Hashimoto's is a cause; hypothyroidism is the result. Not everyone with Hashimoto's has hypothyroidism yet, and hypothyroidism can have other causes, such as thyroid surgery, radioactive iodine treatment or iodine deficiency (the leading cause worldwide).

Treatment

Levothyroxine

When thyroid function is low, treatment is levothyroxine, a synthetic T4 identical to the natural hormone:

• taken once daily, ideally on an empty stomach 30 to 60 minutes before breakfast, or at bedtime
• separate from calcium, iron, antacids and soy by about 4 hours
• dose adjusted using TSH tests every 6 to 8 weeks after changes, then usually yearly
• most people feel better within weeks, although some symptoms take months

Treatment of subclinical hypothyroidism depends on TSH level, symptoms, age and pregnancy plans.

Pregnancy

Untreated hypothyroidism raises the risk of miscarriage and affects the baby's development. People taking levothyroxine usually need a dose increase as soon as pregnancy is confirmed; contact your doctor right away.

Other approaches

• Combination T4/T3 therapy is considered for a small number of people who remain symptomatic despite normal TSH, but evidence of benefit is limited.
• Selenium supplements may lower antibody levels, but there is no clear evidence they change symptoms or outcomes. High doses can be harmful.
• Diet: there is no specific "Hashimoto's diet" proven to help. A gluten-free diet is needed if you also have celiac disease, which is more common with Hashimoto's. Avoid high-dose iodine and kelp supplements.
• Surgery is used only for a large goiter causing pressure symptoms or suspicious nodules.

Complications

• goiter
• high cholesterol and heart disease if untreated
• depression and cognitive slowing
• infertility and pregnancy complications
• rarely, myxedema coma
• a slightly increased risk of thyroid lymphoma, a rare cancer, which presents as a rapidly enlarging thyroid

Frequently asked questions

What is Hashimoto's thyroiditis?

Hashimoto's thyroiditis is an autoimmune disease in which the immune system attacks the thyroid gland, gradually reducing its ability to make hormones. It is the most common cause of hypothyroidism in the US.

What are the symptoms of Hashimoto's?

Symptoms include fatigue, weight gain, feeling cold, constipation, dry skin, thinning hair, low mood, muscle aches, heavy periods and sometimes a swelling in the neck. Many people have no symptoms in the early stages.

Is there a cure for Hashimoto's?

There is no cure for the autoimmune process, but hypothyroidism caused by Hashimoto's is easily treated with daily levothyroxine. Most people live normal, healthy lives with treatment and regular blood tests.

Is there a special diet for Hashimoto's?

No diet has been proven to treat Hashimoto's. A balanced diet is recommended. People who also have celiac disease must avoid gluten. Avoid high-dose iodine or kelp supplements, and take levothyroxine apart from calcium, iron and soy.

Do I need treatment if my thyroid antibodies are positive but my TSH is normal?

Usually not. Positive TPO antibodies with normal thyroid function increase the chance of developing hypothyroidism later, so periodic TSH testing is recommended. Treatment is considered in pregnancy or when TSH rises.