Hashimoto’s thyroiditis is an inflammation of the thyroid gland that frequently results in hypothyroidism, or decreased thyroid gland function. This disorder occurs most commonly in middle-aged women and is caused by the reaction of the immune system against the thyroid gland. It may occur in people with a family history of thyroid diseases or with other autoimmune diseases, especially type 1 diabetes or adrenal insufficiency.

Symptoms are those of hypothyroidism, such as weight gain, increased sensitivity to cold, and fatigue; in addition, the thyroid is markedly enlarged, in many cases causing a visible goiter. It affects about 1 in 10,000 people each year. Thyroiditis, or inflammation of the thyroid gland, has many causes.

The most common cause is Hashimoto’s thyroiditis. This is a chronic inflammatory disorder of the thyroid gland caused by abnormal blood antibodies and white blood cells attacking and damaging thyroid cells. The end result of this so-called “autoimmune” destruction is hypothyroidism caused by the complete absence of thyroid cells. However, in many patients, sufficient thyroid reserve remains to prevent hypothyroidism. Patients with Hashimoto’s thyroiditis are usually, young, middle-aged or older women. They often have no symptoms apart from mild pressure in the thyroid gland and tiredness. In the early stages there is a goitre which is firm, slightly irregular, and sometimes slightly tender. Pain occurs in about 10% of cases.

Subacute Thyroiditis is about ten times less common than Hashimoto’s Thyroiditis. It is a transient form of thyroiditis causing hyperthyroidism but not requiring treatment with radioactive iodine or by thyroidectomy.

There is evidence that subacute thyroiditis is caused by a viral infection since most patients have had a throat infection a few weeks before the thyroiditis. The condition occurs in small epidemics, usually in association with known viral infections.

Another cause of thyroiditis, which occurs about as frequently as subacute thyroiditis, is “silent” thyroiditis. This is so named because there are no symptoms or signs of thyroid inflammation. The patient is hyperthyroid at first and may have the same symptoms as patients with Graves’ hyperthyroidism, but then goes through a hypothyroid phase before full recovery.

Postpartum thyroiditis occurs frequently in women with a past history of thyroid disease who have recently delivered a baby. In most respects, silent and post partum thyroiditis resemble Hashimoto’s thyroiditis except that the gland tends to recover and thyroid hormone treatment need be given for only a few weeks. However, it does differ from subacute thyroiditis in that recurrences are common.