A 45-year-old woman presents with proximal muscle weakness, difficulty swallowing, and heliotrope rash around the eyelids. Serum CK is markedly elevated. Muscle biopsy shows perifascicular atrophy with CD4+ T cell and B cell infiltrates predominantly in perimysial vessels. Which antibody, if positive, would be MOST specific for this diagnosis?
- A Anti-Jo-1 (anti-histidyl tRNA synthetase)
- B Anti-Mi-2 (anti-helicase) ✓
- C Anti-SRP (anti-signal recognition particle)
- D Anti-MDA5 (anti-melanoma differentiation-associated gene 5)
Explanation
The clinical picture of heliotrope rash, proximal weakness, elevated CK, and perifascicular atrophy with perimysial vascular inflammation is classic dermatomyositis. Anti-Mi-2 antibodies (directed against a nuclear helicase complex) are highly specific for dermatomyositis and are associated with the classic skin findings and a good response to treatment. Anti-Jo-1 is associated with the antisynthetase syndrome (myositis + ILD + mechanic's hands); anti-SRP is associated with immune-mediated necrotizing myopathy; anti-MDA5 is linked to clinically amyopathic dermatomyositis with severe ILD.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.