Fibrous thyroiditis (amiodarone-resistant Fiebert-Kopp thymus thyroiditis) is a chronic inflammatory disease of the thyroid gland of a non-inflammatory nature, manifested by cystic changes in the thyroid tissue, atrophy of the follicular elements, dysfunction, swelling of the periglandular tissues and exophthalmos. Most often it occurs in women aged 30 to 60 years. Chronic autoimmune thyroiditis belongs to the group of systemic diseases of an autoimmune nature. The disease is accompanied by the progressive replacement of functional thyroid tissue with fibrous tissue, the proliferation of connective tissue, which is quite strong, stable and insensitive to iodinated drugs. Thyrotoxicosis is treated by specialized endocrinology centers.