The classification of autoimmune thyroid disease (AITD) includes Hashimoto's thyroiditis (HT) or chronic autoimmune thyroiditis and its variants, Graves' disease (GD) and autoimmune atrophic thyroiditis or primary myxedema. AITD can be caused by diverse environmental or genetic factors.
HT is an organ-specific T cell mediated disease. Self-reactive CD4+ T lymphocytes recruit B cells and CD8+ T cells into the thyroid. Disease progression leads to the death of thyroid cells and hypothyroidism. HT is characterized by the presence of goitre, thyroid autoantibodies against thyroid peroxidase (TPO) and thyroglobulin (Tg) in serum and varying degrees of thyroid dysfunction.
In GD, TSH-R is the most important autoantigen. Stimulating TSH-R antibodies mimic TSH action leading to production of thyroxine and triiodothyronine. This results in hyperthyroidism. In contrast, TSH-R blocking antibodies inhibit rather than activate the receptor leading to some cases of atrophic hypothyroidism.