Which antibody is a diagnostic marker for polymyositis?

• A. Anti-Jo-1 antibodies
• B. Anti-La antibodies
• C. Anti-Scl-70 antibodies
• D. Anti-dsDNA antibodies

Answer: (A)

Polymyositis is an inflammatory muscle disease where autoantibody testing helps support the diagnosis. The antibody most characteristic and useful here is anti-Jo-1, an autoantibody against histidyl-tRNA synthetase. It’s the classic myositis-specific antibody and appears in many patients with polymyositis or dermatomyositis, often as part of the antisynthetase syndrome that can include interstitial lung disease, arthritis, Raynaud phenomenon, and skin findings in some cases. The other antibodies point to different diseases: anti-La (SSA) is associated with Sjögren’s and SLE; anti-Scl-70 (topoisomerase I) with diffuse systemic sclerosis; anti-dsDNA with SLE. Therefore, anti-Jo-1 is the most relevant diagnostic marker for polymyositis among these options.