Which autoimmune thyroid disease is associated with exophthalmos and which antibody is typically present?

• A. Hashimoto's; anti-thyroid peroxidase antibodies.
• B. Subacute thyroiditis; no antibodies.
• C. Graves' disease; TSH receptor antibodies (TRAb) are typically present.
• D. Nonautoimmune thyrotoxicosis; TSH receptor antibodies negative.

Answer: (C)

Exophthalmos is a hallmark of Graves' disease, caused by autoimmune antibodies that stimulate the TSH receptor. These TSH receptor antibodies (TRAb), also called thyroid-stimulating immunoglobulins, bind to and activate the receptor, driving hyperthyroidism and contributing to orbital tissue changes that produce eye protrusion. Hashimoto's disease involves anti-thyroid peroxidase antibodies and usually leads to hypothyroidism rather than eye problems. Subacute thyroiditis typically occurs with a painful, inflamed thyroid and often lacks pathogenic antibodies. Nonautoimmune thyrotoxicosis lacks TSH receptor–targeting antibodies altogether.