Hypothyroidism - Causes

Hashimoto's Thyroiditis. The most common form of hypothyroidism in the US is Hashimoto's thyroiditis, a genetic disease named after the Japanese doctor who first described thyroid inflammation in 1912. It occurs in approximately 0.3 to 5 people per 1,000 per year, and women are 15 to 20 times more likely than men to develop this disease.

Hashimoto's disease (chronic thyroiditis)

Click the icon to see an image of Hashimoto's thyroiditis.

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An enlargement of the thyroid gland called a goiter is almost always present and may appear as a cyst-like or fibrous growth in the neck. Hashimoto's thyroiditis is permanent and requires lifelong treatment. Both genetic and environmental factors appear to play a role in its development.

One interesting theory holds that Hashimoto's thyroiditis and Graves' disease (a form of hyperthyroidism) are caused by a similar immunologic dysfunction. Similar immune system substances called antibodies are present in both diseases, and some experts believe that the predominance of one or another antibody determines which of the diseases become manifest. The two diseases, then, are essentially two sides of a single coin.

Click the icon to see an image of Grave's disease.

Atrophic Thyroiditis. Atrophic thyroiditis is similar to Hashimoto's thyroiditis, except a goiter is not present.

Riedel's Thyroiditis. Riedel's thyroiditis is a rare autoimmune disorder, in which scar tissue progresses in the thyroid until it produces a hard stony mass that suggests cancer. Hypothyroidism develops as healthy tissue is gradually replaced. Surgery is usually required, although early stages may be treated with tamoxifen, corticosteroids, or other immunosuppressive agents.

Autoimmune Thyroiditis Due to Pregnancy. Hypothyroidism may also occur in women who develop antibodies to their own thyroid during pregnancy, causing an inflammation of the thyroid after delivery.

Subacute Thyroiditis

Subacute thyroiditis is a temporary condition that passes through three phases: hyperthyroidism, hypothyroidism, and then a return to normal thyroid levels. Patients may exhibit symptoms of both hyperthyroidism and hypothyroidism (e.g., rapid heartbeat, nervousness, weight loss), and they can feel extremely sick. Symptoms last about six to eight weeks and then resolve in the great majority of patients, although each form carries some risk for becoming chronic. Experts estimate that subacute thyroiditis is responsible for 10% of all cases of hypothyroidism.

There are three forms but they all have a similar course:

Painless Postpartum Subacute Thyroiditis. Postpartum thyroiditis is an autoimmune condition that occurs in up to 10% of pregnant women and tends to develop between 4 and 12 months after delivery. In most cases, a woman develops a small, painless goiter. It should be noted that only about a third of these women go through the classic three phases typical of other forms of subacute thyroiditis. Although 80% of women with this condition have normal thyroid function within a year, some evidence suggests that half of women with this condition develop permanent hypothyroidism within seven years. Women at higher risk are those who have had recurrent episodes after previous pregnancies and women who have other autoimmune disorders. It is generally self-limiting and requires no therapy unless the hypothyroid phase is prolonged. In such case, thyroxine replacement may be given for a few months. If the hyperthyroid phase requires treatment, beta blockers are typically used.