A 31-year-old woman visits the ambulatory clinic complaining of severe fatigue, low-grade fevers, and generalized joint achiness that has gradually worsened over the past two months. She recently started a landscaping business and notes that spending hours in the sun causes a bright, flat red rash to appear across her nose and cheeks. On physical examination, her temperature is (). A confluent, erythematous rash is visible over the malar eminences, notably sparing the nasolabial folds. She has mild synovial thickening and tenderness in the wrists and proximal interphalangeal joints bilaterally. Which of the following laboratory findings is most specific for this patient's likely diagnosis?
- Anti-double-stranded DNA antibodiesAnswer
- BAntinuclear antibodies
- CAnti-cyclic citrullinated peptide antibodies
- DAnti-histone antibodies
- ERheumatoid factor
Answer
Anti-double-stranded DNA antibodies
The correct answer is Anti-double-stranded DNA antibodies. This patient presents with a classic clinical picture of Systemic Lupus Erythematosus (SLE), characterized by a photosensitive malar rash that classically spares the nasolabial folds, fatigue, low-grade fevers, and non-erosive polyarthritis. In the diagnostic evaluation of suspected SLE, Antinuclear antibodies (ANA) are typically checked first because they are highly sensitive (positive in >95% of patients); however, they lack specificity. To confirm the diagnosis, highly specific autoantibodies such as Anti-double-stranded DNA (anti-dsDNA) or Anti-Smith antibodies are required. Anti-dsDNA is not only highly specific for SLE, but its titers frequently fluctuate with disease activity and correlate strongly with the development of lupus nephritis.
Step-by-Step Solution
Key Concept
Diagnosis of Systemic Lupus Erythematosus (SLE) and distinguishing between sensitive screening tests (ANA) and highly specific confirmatory tests (Anti-dsDNA, Anti-Smith).