AUTOIMMUNE DISORDERS AFFECTING ENDOCRINE GLANDS
Autoimmune disorders of the thyroid gland are among the most common autoimmune disorders. Some will be discussed. Autoimmune thyroiditis, also known as Hashimoto’s thyroiditis, results in hypothyroidism and myxedema. The disease presents, typically, in women of middle age who are overweight, lethargic, constantly feel cold, are constipated and have coarse, dry hair and skin. The thyroid is swollen with a generally painless goiter, but which has a rubbery consistency when palpated. A biopsy of the thyroid shows infiltration with both CD8+ and CD4+ T lymphocytes that progressively destroy the thyroid gland. Patients also have antibodies to thyroglobulin and to thyroid peroxidase, which can be determined by
ELISA . Immunohistochemical techniques can show the patient’s serum to have antibodies that bind to microsomal antigens in sections of normal thyroid (Figure 5.4). Patients may be given thyroxine to treat the myxedema, and thyroidectomy may be required. The prognosis for patients with Hashimoto’s thyroiditis is good.
In Graves disease, patients suffer symptoms of thyrotoxicosis: are thin, have a high resting pulse rate, constantly feel hot, have bulging eyes, or exophthalmos, due to growth of tissue around the orbit of the eye and may suffer diarrhea and general agitation. They have nodules in the thyroid that are foci of infiltrating T lymphocytes. Low levels of antibodies to thyroid microsomal antigens are seen in the plasma. However, more than 90% of patients have antibodies to the thyroid stimulating hormone (TSH) receptor on the surface of thyroid cells. These antibodies bind to the receptor and stimulate the production of thyroid hormone (Figure 5.5). This production is not regulated by the usual negative feedback mechanisms leading to the disease symptoms. Graves disease may be treated successfully by destruction of thyroid tissue. This can be achieved by its surgical removal or by giving the patient radioactive iodine that becomes concentrated in the thyroid. When women with Graves disease are pregnant, autoantibodies to TSH cross the placenta and the baby is born with thyrotoxicosis. Urgent treatment is required but, in time, the baby recovers as its levels of maternally derived antibodies drop.
Both insulin dependent diabetes mellitus Type 1 and Addison’s disease are discussed extensively. The former is caused by an autoimmune destruction of the insulin-producing cells in the pancreas; the latter by autoimmune damage to the adrenal cortex. Both diseases are fatal unless treated by replacing the missing hormones.