Autoimmune thyroiditis (AT), also known as Hashimoto's disease, is a chronic inflammatory disorder of the thyroid gland that is caused by abnormal blood antibodies and white blood cells that mistakenly attack and damage healthy thyroid cells. It is a progressive disease that may destroy the thyroid gland, causing thyroid hormone deficiency (hypothyroidism). Autoimmune thyroiditis presents with various combinations of symptoms, making diagnosis difficult. This disease can occur at any age, but is most often seen in middle-aged women. In rare cases, it may be associated with other autoimmune endocrine disorders.
Autoimmune thyroiditis is a common cause of primary hypothyroidism. Affected individuals complain of enlargement of the thyroid gland or fullness in the throat. It causes a non-tender lump (goiter). This abnormal lump on the front of the neck is smooth or nodular, firm and more rubbery in consistency than the normal thyroid. In 90% of cases, it is painless. Thyroid function blood studies initially fall within the normal limits, until the disease has progressed sufficiently to cause the lack of thyroid hormone. It may take months or even years for the disorder to be detected.
Some people don’t exhibit any symptoms at all. Others may experience various combinations of intolerance to cold, mild weight gain, fatigue, constipation, presence of a goiter, dry skin, hair loss, irregular or heavy menstrual periods, a small or shrunken thyroid gland (late stage) and difficulty in concentrating or thinking.
AT is an autoimmune disorder caused by infiltration of the thyroid gland with lymphocytes (white blood cells), resulting in the progressive destruction of the thyroid gland and eventually causing hypothyroidism. Autoimmune diseases begin when the body’s natural defenses against disease, such as antibodies, lymphocytes, etc., attack healthy tissue for unknown reasons.
There is a genetic predisposition to develop autoimmune thyroiditis. It occurs more often among people who have a family history of the disease. Mutations in two genes on chromosome 8 and chromosome 2 (8q23-q24 and 2q33) appear to be necessary to establish the tendency for genetic transmission of the disorder.
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 8q23-q24” refers to a region on the long arm of chromosome 8 between bands 23 and 24. The phrase “chromosome 2q33” refers to band 33 on the long arm of chromosome 2. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Autoimmune thyroiditis can occur in men and women at any age, but is most frequently seen in women between the ages of 30 and 50. A family history of thyroid disorders is common. The incidence is increased in patients with chromosomal disorders including Turner’s, Down’s and Klinefelter’s syndromes. (For more information about these disorders, choose “Turner”, “Down” and “Klinefelter” as your search terms in the Rare Disease Database.)
Autoimmune thyroiditis is diagnosed in most cases by means of blood tests that measure the amount of various thyroid hormones in the patient's blood. One of these hormones is thyroxine (T4), the level of which may be elevated in persons with this disorder. Thyroxine is a precursor of T3, an active form of thyroid hormone. The blood levels of each of these hormones are regulated by the amount of thyroid stimulating hormone. Accurate tests are available to measure the concentrations of each.
In some cases, a biopsy of the thyroid gland may be necessary for a definitive diagnosis.
Treatment of autoimmune thyroiditis consists of replacing thyroid hormone in the body. This will alleviate the symptoms and produce a marked reduction in the gland size within 2 to 4 weeks. Once thyroid hormone has been started, it should be continued for life, since it is unlikely that the disease will regress spontaneously.
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