A 37-year-old woman with a neck mass has circulating antibodies against thyroid peroxidase and thyroglobulin. Which diagnosis is most likely?

• A. Graves disease
• B. Subacute thyroiditis
• C. De Quervain's thyroiditis
• D. Hashimoto thyroiditis

Answer: (D)

Autoimmune destruction of the thyroid with circulating antibodies against thyroid components points to Hashimoto thyroiditis. In this condition, the immune system forms antibodies to thyroid peroxidase and thyroglobulin, leading to progressive lymphocytic infiltration and destruction of thyroid follicles. The result is a painless, firm goiter and often hypothyroidism as thyroid function declines. Histology typically shows Hurthle cell changes and lymphoid germinal centers.

In contrast, Graves disease is driven by antibodies to the TSH receptor, causing hyperthyroidism with possible ophthalmopathy. Subacute (De Quervain) thyroiditis presents with a painful, tender thyroid and an inflammatory picture, usually after a viral illness, with transient thyrotoxicosis rather than autoimmune destruction. Thus, the combination of anti-TPO and anti-thyroglobulin antibodies most strongly supports Hashimoto thyroiditis.