American Board of Internal Medicine (ABIM) Certification Practice Exam

Which autoantibody is primarily associated with diffuse scleroderma?

1. anti-smooth muscle

2. Anti-Scl-70 (anti-DNA Topoisomerase I)

3. Anti-U1 RNP (ribonucleoprotein)

4. anti endomysial

The correct answer is: Anti-Scl-70 (anti-DNA Topoisomerase I)

Anti-Scl-70, also known as anti-DNA topoisomerase I, is primarily associated with diffuse scleroderma, which is a subtype of systemic sclerosis. This association is significant because patients with diffuse scleroderma typically exhibit rapid skin involvement, with thickening occurring over large areas of the body and often involving internal organs early in the course of the disease. The presence of anti-Scl-70 antibodies indicates a higher risk for more severe disease manifestations, including pulmonary complications and renal crises, which can develop more precipitously compared to limited scleroderma. In contrast to diffuse scleroderma, limited scleroderma is generally associated with anti-centromere antibodies and has a slower progression with skin involvement primarily confined to the extremities and face. While the other autoantibodies listed are important in the context of various autoimmune conditions, they do not have the same strong association with diffuse scleroderma as anti-Scl-70. For example, anti-smooth muscle antibodies are more commonly seen in autoimmune hepatitis. Anti-U1 RNP antibodies are associated with mixed connective tissue disease and not specifically with diffuse scleroderma. Anti-endomysial antibodies are linked to celiac disease and have no