Serum-negative autoimmune thyroiditis: what’s in a name?

Excerpt

Chronic autoimmune thyroiditis (CAT) is the main cause of hypothyroidism in the general population. Autoantibodies to thyroperoxidase (TPO) and to thyroglobulin (Tg) are the circulating hallmark of this autoimmune thyroid disease. Positive tests for TPO Ab and Tg Ab are present in nearly 90 (TPOAb) and 60 % (Tg Ab) of hypothyroid patients with CAT. This implies that despite the high sensitivity of modern assay methods for thyroid auto Ab, there still is a considerable number of patients presenting with hypothyroidism in whom the humoral markers of thyroid autoimmunity are found to be negative. The widespread use of ultrasound in the diagnostic work-up of thyroid diseases allowed to ascertain that most of these patients display a hypoechoic pattern of the thyroid at ultrasound [1]. Further characterization of this echographic finding indicated that this peculiar echopattern is mainly due to lymphocytes infiltrating the thyroid parenchyma, as confirmed by fine needle aspiration biopsy. On this basis, a new clinical entity was identified, the so-called serum-negative chronic autoimmune thyroiditis (SN-CAT). …