Autoimmune Diseases of the Thyroid

Autoimmunity to thyroid antigens is the most common cause of thyroid diseases including Hashimoto's thyroiditis (HT), Graves' disease (GD), and primary myxedema (PM). Different autoimmune diseases of the thyroid share similar

Fig. 14.1 Regulation of thyroid hormone production. The upper panel shows a normal hypothalamus-pituitary-thyroid axis, which maintains hormonal homeostasis and regulates normal thyroid function. The middle panel illustrates the effects of stimulatory Abs (TSAb) as seen in patients with Graves' disease. The lower panel shows the effects of blocking Abs (TSBAb) as seen in patients with primary myxedema.

Fig. 14.1 Regulation of thyroid hormone production. The upper panel shows a normal hypothalamus-pituitary-thyroid axis, which maintains hormonal homeostasis and regulates normal thyroid function. The middle panel illustrates the effects of stimulatory Abs (TSAb) as seen in patients with Graves' disease. The lower panel shows the effects of blocking Abs (TSBAb) as seen in patients with primary myxedema.

immunological characteristics and are thought to be interrelated. However, particular thyroid antigens, immunological abnormalities, symptoms, and clinical courses are associated with specific thyroid diseases. For example, it is well known that anti-thyroid antibodies circulate in the serum of patients that suffer from HT and GD, but it is generally accepted that HT is primarily a T cellmediated disease in which thyroglobulin-specific T cells infiltrate the thyroid and cause glandular destruction that results in hypothyroidism. In contrast,

GD, the most prevalent of the TSHR-mediated autoimmune diseases, is mediated by anti-TSHR autoantibodies that can act as TSH agonists and cause hyperthyroidism. However, if the anti-TSHR antibodies act as TSH antagonists, they can result in primary myxedema (PM), which is characterized by hypothyr-oidism.

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