Autoimmune Thyroid Disease

How autoimmune thyroid disease develops

The thyroid, a butterfly-shaped gland at the front of the neck, makes thyroid hormones (T4 and T3) that set the body's metabolic rate. The pituitary gland controls it with thyroid-stimulating hormone (TSH).

In autoimmune thyroid disease, the immune system loses tolerance to thyroid proteins. Genes (including HLA types and immune-regulating genes) and triggers such as infection, pregnancy, high iodine intake, smoking and stress interact to start the process. The result depends on which antibodies dominate.

Hashimoto's vs Graves' disease

Some people move between the two, and a brief overactive phase (hashitoxicosis) can occur early in Hashimoto's.

Symptoms of Hashimoto's (underactive thyroid)

Hashimoto's thyroiditis develops slowly and is the most common cause of hypothyroidism in iodine-sufficient countries.

• tiredness and sluggishness
• weight gain
• feeling cold
• constipation
• dry skin and hair thinning
• low mood and poor concentration
• heavy or irregular periods
• muscle aches and stiffness
• a swollen thyroid (goiter)

Symptoms of Graves' disease (overactive thyroid)

Graves' disease is the most common cause of hyperthyroidism.

• weight loss despite a good appetite
• fast or irregular heartbeat, palpitations
• tremor of the hands
• heat intolerance and sweating
• anxiety, irritability and poor sleep
• frequent bowel movements
• muscle weakness
• lighter or less frequent periods
• a smooth, enlarged thyroid

Thyroid eye disease

About a quarter to a third of people with Graves' develop thyroid eye disease: gritty, red, watering eyes, puffy lids, bulging eyes, double vision, and rarely compression of the optic nerve. Smoking makes it much worse.

Related autoimmune conditions

People with autoimmune thyroid disease are more likely to have other autoimmune conditions, including type 1 diabetes, celiac disease, vitiligo, pernicious anemia, rheumatoid arthritis and Addison's disease. Postpartum thyroiditis is a related autoimmune flare in the year after childbirth.

Diagnosis

• TSH: the main screening test. High in hypothyroidism, very low in hyperthyroidism
• Free T4 (and sometimes T3): confirm and measure the degree of dysfunction
• TPO antibodies: positive in about 90% of people with Hashimoto's. Also found in about 10% of the general population without disease, who have a higher risk of future hypothyroidism
• TSH receptor antibodies: confirm Graves' disease
• Thyroid ultrasound: for goiter or nodules
• Radioactive iodine uptake scan: sometimes used to distinguish Graves' from other causes of hyperthyroidism

Subclinical disease, with abnormal TSH but normal T4, is common. Treatment depends on TSH level, symptoms, age and pregnancy plans. See subclinical hypothyroidism.

Treatment

Hashimoto's thyroiditis

• Levothyroxine (synthetic T4) taken once daily on an empty stomach, 30 to 60 minutes before breakfast and apart from calcium, iron and antacids
• dose adjusted by TSH tests every 6 to 8 weeks until stable, then yearly
• people with positive antibodies but normal thyroid function are usually monitored

There is no strong evidence that gluten-free diets, selenium supplements or iodine supplements cure Hashimoto's in people without celiac disease. Excess iodine can worsen it.

Graves' disease

• Antithyroid drugs: methimazole (or propylthiouracil in early pregnancy) for 12 to 18 months. About half of people relapse after stopping
• Beta blockers: quickly relieve palpitations, tremor and anxiety
• Radioactive iodine: a single drink or capsule that shrinks the gland. Most people later need levothyroxine. Not used in pregnancy or active moderate-to-severe eye disease
• Thyroidectomy: surgical removal, useful for large goiters, eye disease or pregnancy planning
• Eye disease treatment: stopping smoking, lubricants, selenium for mild cases, and steroids, teprotumumab or surgery for more severe disease

Pregnancy

Thyroid hormone is vital for a baby's brain development. Women with Hashimoto's usually need a levothyroxine dose increase as soon as pregnancy is confirmed. Graves' antibodies can cross the placenta, so pregnancies need specialist monitoring.

Outlook

Both conditions are lifelong tendencies but are very well controlled with treatment. People with treated Hashimoto's lead normal lives with daily medicine and periodic tests. Graves' disease can go into remission, and those treated with radioactive iodine or surgery do well on levothyroxine.

Frequently asked questions

What is the difference between Hashimoto's and Graves' disease?

Both are autoimmune thyroid diseases. In Hashimoto's, the immune system damages the thyroid, causing underactivity. In Graves', antibodies overstimulate the thyroid, causing overactivity and sometimes eye problems. They are diagnosed with different antibody tests and treated differently.

What tests diagnose autoimmune thyroid disease?

TSH and free T4 blood tests show whether the thyroid is under- or overactive. TPO antibodies point to Hashimoto's thyroiditis. TSH receptor antibodies point to Graves' disease. Ultrasound may be used to examine the gland.

Can autoimmune thyroid disease be cured?

Hashimoto's is lifelong but fully controlled with daily levothyroxine. Graves' disease can go into remission after antithyroid drugs, and radioactive iodine or surgery permanently stop overactivity, after which levothyroxine is usually needed.

Can you have thyroid antibodies with normal thyroid function?

Yes. Positive TPO antibodies are common, and many people have normal thyroid function. They have a higher chance of developing hypothyroidism over time, so doctors often recommend periodic TSH tests, especially before and during pregnancy.

Does diet affect autoimmune thyroid disease?

No specific diet cures it. A balanced diet with adequate but not excessive iodine is recommended. People with celiac disease, which is more common with autoimmune thyroid disease, need a gluten-free diet. Avoid high-dose iodine and kelp supplements.