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So Board Answer
A 26-year-old female with a history of bipolar disorder sees you for follow-up of chronic joint pain. The review of systems is positive for intermittent rashes on the dorsal hands and face and left-sided pleuritic chest pain. An examination reveals tender swelling of the hand and wrist joints bilaterally. Examination of the lungs reveals diminished breath sounds at the left base with point-of-care ultrasonography findings consistent with a small pleural effusion. Initial laboratory tests are significant for a platelet count of 96,000/mm3 (N 130,000–450,000), a positive antinuclear antibody test with a 1:80 titer (N <1:40), and negative Lyme disease and HIV tests.
Which one of the following would help confirm your suspected diagnosis?
A. Elevated anticyclic citrullinated peptide antibodies
B. Elevated anti–smooth muscle antibodies
C. Elevated anti-centromere antibodies
D. Low complement levels
E. Positive HLA-B27
The clinical findings on examination, including symmetric polyarthritis, thrombocytopenia, positive antinuclear antibodies (ANAs), and pleural effusion, meet the American College of Rheumatology criteria for a diagnosis of systemic lupus erythematosus (SLE). The rash and the patient’s neuropsychiatric history may also factor into the diagnosis, but they are not described specifically in this case. A positive ANA is sensitive but not specific for SLE. Although additional laboratory testing may not be needed to confirm SLE in this case due to classic clinical findings, low complement levels help confirm SLE and may be helpful because the ANA is only mildly elevated. Elevated anticyclic citrullinated peptide antibodies help confirm a diagnosis of rheumatoid arthritis. Anti–smooth muscle antibodies are used to confirm autoimmune hepatitis, which can also cause an elevated ANA. Anti-centromere antibodies, a subset of ANAs, are more closely associated with systemic sclerosis. A positive HLA-B27 test is associated with the seronegative spondyloarthropathies, such as psoriatic arthritis.
Ref: Lam NC, Ghetu MV, Bieniek ML: Systemic lupus erythematosus: Primary care approach to diagnosis and management. Am Fam Physician 2016;94(4):284-294.