Atrophic Autoimmune Thyroiditis

Atrophic autoimmune thyroiditis (AAT) is an organ-specific autoimmune disease characterized by thyroid autoantibodies, functional hypothyroidism, and absence of goiter. Atrophic autoimmune thyroiditis is a rare entity that occurs most frequently between 40 and 60 years of age. Immunogenetic analysis suggests that AAT may differ from Hashimoto’s disease. Genetic and environmental factors interact, leading to autoantigens with autoantibody formation. Atrophic autoimmune thyroiditis is a Th2 disease with blocking anti-TSH receptor antibodies. Hashimoto’s thyroiditis, primary myxedema, or AAT, and Graves’ disease could be different expressions of a similar process. The immune response may include cytotoxic antibodies, stimulatory antibodies, blocking antibodies, or cell-mediated immunity. The clinical presentation varies from asymptomatic AAT to overt hypothyroidism and myxedema. The pathological features are an atrophic thyroid gland with lymphocytic infiltration and fibrous tissue replacing normal thyroid parenchyma. There are no current diagnostic criteria for AAT. We propose the following bases for AAT diagnosis: clinic or subclinical hypothyroidism, positive thyroid stimulation-blocking antibodies, and thyroid ultrasound with diffuse low thyroid echogenicity associated with a reduced thyroid volume. In asymptomatic AAT, preventive thyroid replacement therapy is indicated in patients with elevated basal TSH levels.