Graves Disease and Hashimoto Thyroiditis: Autoimmune Conditions of the Thyroid Gland
Many devastating health conditions can result the body's immune system produces antibodies that are not normal to physiological function. Autoimmune diseases are those that result from abnormal antibodies. In most cases the antibodies and other agents of the immune system cause disease by destroying tissue, but in some cases antibodies produce their effects by acting like hormones or drugs.
Most people interested enough to read this will be aware of the meanings of hyperthyroidism vs. hypothyroidism and may be familiar with the notorious symptoms. Hypothyroidism is a state in which the body slows down and grows colder due to a lack of thyroxine (FT4) and free triiodothyronine (FT3), while hyperthyroidism is the opposite. Tachycardia, insomnia, warm extremities and ophthalmopathies such as classic symptoms of a hyperthyroid state. This can result from an adenoma (a benign tumor) in the thyroid, in which case a lump would be present.
Diffuse enlargement of the thyroid, on the other hand, can result either from over stimulation of the gland by high levels of thyroid stimulating hormone (TSH) from a pituitary macroadenoma, or from stimulation by antibodies. The former case results in elevated levels of TSH as well as thyroid hormones. It is fairly uncommon, and often includes symptoms of pituitary compression, such as visual field problems and reductions in other pituitary hormones.
A much more common condition of diffuse thyroid activity and enlargement is Graves disease. Named for the 19th century physician, Robert J. Graves, the condition results from autoantibodies called thyroid-stimulating immunoglobins (TSIs), or thyroglobulin autoantibodies, which happen to mimic the effects of TSH on thyrotropin receptors. Thus, they function essentially as hormones. Graves disease features orange thickening of the skin known by its French term peau d'orange, which is thought to result from an inflammatory response to the infiltration of the TSIs under the skin. Since the thyroid gland is being stimulated, the high levels of FT4 (T4) inhibit pituitary production of TSH due to a negative feedback mechanism.
Thyroid peroxidase antibodies are another type of autoantibody that affect the thyroid. They are found most commonly in connection with Hashimoto thyroiditis. As opposed to Graves disease in which the overall effect of the antibodies is thyroid stimulation, Hashimoto disease is characterized by gradual destruction of thyroid tissue, presenting as chronic hypothyroidism with bouts of hyperthyroidism. Hashimoto thyroiditis can occur in association with Addison disease and in such case the condition is known as Schmidt syndrome.