Positive thyroid peroxidase antibody with hypothyroidism is most consistent with which autoimmune thyroid disease?

• A. Graves disease
• B. Hashimoto thyroiditis
• C. Normal thyroid
• D. Pituitary tumor

Answer: (B)

Autoimmune thyroid antibodies are a key clue to the underlying disease. Thyroid peroxidase antibodies target an enzyme involved in making thyroid hormones, and their presence most strongly points to Hashimoto thyroiditis. In Hashimoto’s, the immune system gradually attacks the thyroid, causing destruction of thyroid tissue and reduced hormone output, which leads to hypothyroidism. That pattern fits best with the scenario of positive TPO antibodies plus hypothyroidism.

Graves disease, while autoimmune, typically presents with hyperthyroidism due to antibodies that stimulate the TSH receptor, not destruction of the thyroid. A normal thyroid would not have this autoimmune antibody pattern, and a pituitary tumor would cause hypothyroidism through central (pituitary) dysfunction without thyroid-specific antibodies.