10) 自己免疫性甲状腺疾患

Autoimmune thyroid diseases : Hashimoto's thyroiditis and Graves' disease

自己免疫性甲状腺疾患にはBasedow病と橋本病がある．Basedow病は甲状腺機能亢進症，橋本病は甲状腺機能低下症の原因である．血中甲状腺ホルモンが高値になり，甲状腺中毒症状のあるものを甲状腺中毒症という．Basedow病の病因は自己免疫異常により甲状腺刺激物質TRAbができることである．この異常甲状腺刺激物質はリンパ球がつくる抗体で，TSH受容体に対する抗体TRAbである．このTRAbは甲状腺刺激抗体TSAbである．橋本病(慢性甲状腺炎)では甲状腺濾胞細胞が変性・萎縮し，甲状腺機能低下症に陥る．橋本病の甲状腺組織所見は①高度リンパ球浸潤，②線維増殖，そして③濾胞上皮細胞変性の3つである．甲状腺抗体TGAb・TPOAbが陽性になる．本稿では，Basedow病と橋本病について概説

Autoimmune thyroid diseases (Hashimoto's thyroiditis and Graves' disease) occur when the thyroid is attacked by the immune system.　Hashimoto's causes hypothyroidism.　Graves' causes hyperthyroidism.　These diseases occur more in women than in men.　Hashimoto's and Graves' have a genetic component because they sometimes run in families.　The immune system mistakes thyroid tissue for a foreign and potentially dangerous invader of the body and attacks it.　Hypothyroidism is the hallmark of Hashimoto's.　Hypothyroidism results in a slowing of the body's chemical processes and metabolism (weight gain, fatigue, and depression).　Hyperthyroidism is the hallmark of Graves' disease.　Hyperthyroidism results in increases of metabolism (nervousness, anxiety, and palpitation).　Making a diagnosis begins with taking the history, including symptoms, and completing a physical examination.　A goiter in the neck may be detected.　A blood test is performed to determine levels of TSH and T₄ and T₃.　High TSH levels and low T₄ levels indicate hypothyroidism and may indicate a diagnosis of Hashimoto's.　Low TSH levels and high T₄ levels indicate hyperthyroidism and may indicate a diagnosis of Graves'.　Hashimoto's is characterized by the destruction of thyroid follicle cells by various cell- and antibody-mediated immune processes.　Hashimoto's patients have TPOAb, TGAb, and TSH-stimulation blocking Ab (TSBAb).　Graves' is an autoimmune disease characterized by hyperthyroidism due to TSAb.　TSAb is TRAb, which stimulates the thyroid.　There are two types of TRAb ; TSAb and TSBAb.　TSAb causes Graves' hyperthyroidism.　TSBAb causes hypothyroidism.　MMI is used for the treàtment of Graves' hyperthyroidism, and T4 for that of hypothyroidism.