The patient’s symptoms are indicative of rheumatoid arthritis (RA). Anti-citrullinated protein antibody (ACPA, or anti-CCP) has greater than 90% specificity for diagnosing RA.
RA most commonly presents in females 20-40 years old. Joint pain is symmetric with stiffness worse in the morning and improving with use. The proximal interphalangeal and metacarpophalangeal joints are often deformed, while distal interphalangeal joints are spared. Patients may also have systemic symptoms such as fever and fatigue.
Wasserman reviews the diagnosis of RA. The likelihood of RA increases according to the number of small joints involved. In addition to ACPA, elevated rheumatoid factor, C-reactive protein level, or erythrocyte sedimentation rate (ESR) suggest RA.
Demoruelle and Deane review the clinical significance of ACPAs. ACPAs are highly specific for RA. The test is helpful in the diagnosis of RA and can also be used to monitor the course and outcomes of disease.
Illustration A shows an x-ray of a hand from a patient with severe rheumatoid arthritis. Note involvement of the metacarpophalangeal joints and proximal interphalangeal joints.
Answer 1: Rheumatoid factor is an autoantibody directed against the Fc portion of IgG. It is more sensitive but less specific than ACPA.
Answer 2: Anti-nuclear antibody is a sensitive, but not specific, marker for systemic lupus erythematosus.
Answer 4: Anti-centromere antibody is a marker for CREST syndrome.
Answer 5: Anti-smooth muscle antibody is a marker for autoimmune hepatitis.
Wasserman AM. Diagnosis and management of rheumatoid arthritis. Am Fam Physician. 2011 Dec 1;84(11):1245-52
PMID:22150658 (Link to Abstract)
Demoruelle MK, Deane K. Antibodies to citrullinated protein antigens (ACPAs): clinical and pathophysiologic significance. Curr Rheumatol Rep. 2011 Oct;13(5):421-30. Review
PMID:21713412 (Link to Abstract)
USMLE World Step 1 Qbank Question #754. Copyright © USMLEWorld, LLC 2012