A reduction in the size of the thyroid gland may cause serious effects, such as atrophic thyroiditis. Atrophic thyroiditis is an autoimmune thyroiditis, also known in the past as idiopathic hypothyroidism and primary mucous edema. It manifests as thyroid atrophy, i.e., a reduction in the size of the thyroid gland, most of which is accompanied by clinical hypothyroidism. Thyrotropin receptor stimulating blocking antibodies (TSBAb) are associated with hypothyroidism due to atrophic thyroiditis. In hypothyroidism, the main manifestations are fatigue, chills and cold, puffy eyelids, memory loss, and expression of indifference. Severe hypothyroidism may also cause slow heart rate, pericardial effusion, etc. Hypercholesterolemia may occur when lipid metabolism is affected. If the size of the thyroid gland shrinks during pregnancy, resulting in hypothyroidism, it may also affect the development of the fetus, and the child will easily become cretinism after birth. In general, there is no treatment for atrophic thyroiditis that addresses the cause of the condition, and limiting iodine intake may help to prevent continued autoimmune destruction of the thyroid gland. If hypothyroidism is present, thyroid hormone supplementation is required. It is therefore recommended that anyone with a reduced thyroid volume seek medical attention for further investigation and treatment as prescribed by the doctor.