A 45-year-old woman comes to the office due to a long history of joint pain, swelling, and stiffness. She recently immigrated to the United States and had little access to medical care in her original country. On physical examination, her proximal interphalangeal and metacarpophalangeal joints are tender and swollen bilaterally, and her fingers appear significantly deformed. Subcutaneous nodules are palpated near the elbow. Laboratory studies are obtained to confirm the diagnosis. This patient's serum is most likely to contain IgM antibodies against which of the following substances?

Question

A 45-year-old woman comes to the office due to a long history of joint pain, swelling, and stiffness.  She recently immigrated to the United States and had little access to medical care in her original country.  On physical examination, her proximal interphalangeal and metacarpophalangeal joints are tender and swollen bilaterally, and her fingers appear significantly deformed.  Subcutaneous nodules are palpated near the elbow.  Laboratory studies are obtained to confirm the diagnosis.  This patient's serum is most likely to contain IgM antibodies against which of the following substances?

Quizplus · Accepted Answer

11ec160b_37e4_b7cb_9249_5bf4a54abea0_MD0001_00 Bilateral pain, stiffness, and deformity of the proximal interphalangeal and metacarpophalangeal joints are typical of advanced rheumatoid arthritis (RA). Morning stiffness, tenderness, and edema of the affected joints predominate early in this disease. Later, osteopenia, erosions, and joint space narrowing lead to decreased range of motion and deformities (eg, swan neck, ulnar deviation). Patients can also develop rheumatoid nodules, firm, nontender, subcutaneous nodules that occur at pressure points such as the elbows or forearms. RA is due to failure of immune tolerance, with development of an autoreactive immune response directed against joint components (eg, type II collagen, citrullinated vimentin). CD4⁺ T-helper cells become activated by these self-antigens and release cytokines that promote chronic inflammatory synovitis. CD4⁺ T cells also induce B cells to synthesize rheumatoid factor and anti-citrullinated protein antibodies (ACPAs). Rheumatoid factor is an antibody (typically IgM) specific for the Fc component of IgG. Rheumatoid factor binds circulating IgG and ACPAs bind modified self-proteins, forming immune complexes that deposit on the synovium and cartilage. These complexes activate complement in those locations, contributing to chronic inflammation and joint destruction. (Choice A) Anticentromere antibodies are found in the majority of patients with CREST syndrome. (Choice B) Antibodies to double-stranded DNA (anti-dsDNA) are specific for systemic lupus erythematosus. (Choice D) Antimitochondrial antibodies are found in patients with primary biliary cholangitis. (Choice E) The presence of antinuclear antibodies is a nonspecific finding in many connective tissue disorders. These can occur in IgM form, but would be found less frequently than rheumatoid factor in patients with RA. (Choice F) Antiphospholipid antibodies can be found in patients with systemic lupus erythematosus and antiphospholipid antibody syndrome. Antiphospholipid antibodies cause a hypercoagulable state with paradoxical PTT prolongation. (Choice G) The Monospot test assesses the serum's ability to agglutinate sheep erythrocytes. It is positive in the presence of heterophile antibodies and is used to diagnose infectious mononucleosis due to Epstein-Barr virus. Educational objective: Rheumatoid arthritis results from an immune response directed against autoantigens in the joints. Infiltrating CD4⁺ T cells secrete cytokines that promote inflammatory synovitis. They also stimulate B cells to produce rheumatoid factor (IgM antibody specific for Fc component of IgG) and anti-citrullinated protein antibodies that contribute to chronic inflammation and joint destruction.

A 45-Year-Old Woman Comes to the Office Due to a Long