American Board of Internal Medicine (ABIM) Certification Practice Exam

Patients with Mixed Connective Tissue Disease (MCTD) must have positive anti-U1-RNP antibodies and at least how many additional features?

1. One

2. Two

3. Three

4. Four

The correct answer is: Three

In Mixed Connective Tissue Disease (MCTD), the diagnosis is predominantly characterized by the presence of anti-U1 ribonucleoprotein (RNP) antibodies, which serve as a serological hallmark of the disease. However, this serological finding is not sufficient on its own for diagnosis. In addition to positive anti-U1-RNP antibodies, patients must demonstrate at least three other clinical features that are commonly associated with MCTD. These features typically overlap with symptoms from other connective tissue diseases, such as systemic lupus erythematosus, polymyositis, and scleroderma. Common clinical manifestations considered in the diagnostic criteria include: 1. Raynaud's phenomenon 2. Swollen hands or fingers 3. Muscle weakness or myositis 4. Arthritis 5. Esophageal dysfunction 6. Pulmonary hypertension 7. Skin changes Having multiple features helps to differentiate MCTD from other connective tissue diseases and establishes a more definitive diagnosis. Hence, the requirement for three additional features alongside the positive autoantibody test provides a broader understanding of the patient's condition and aligns with the necessary criteria for diagnosing MCTD. This comprehensive approach ensures that patients receive appropriate treatment and management tailored to their specific symptoms and