A 40-year-old with proximal muscle weakness and anti-Jo-1 antibodies; most likely diagnosis?

• A. Dermatomyositis
• B. Polymyositis
• C. Polymyalgia rheumatica
• D. Systemic lupus erythematosus

Answer: (B)

Proximal symmetric muscle weakness in adults with an antisynthetase antibody points to an inflammatory myopathy, specifically the antisynthetase syndrome. The anti-Jo-1 antibody is classically associated with this condition and with inflammatory myopathies driven by immune-mediated muscle fiber damage. Dermatomyositis would add characteristic skin findings such as a heliotrope rash or Gottron papules, which aren’t described here, making polymyositis the more likely diagnosis. Polymyalgia rheumatica occurs in older individuals with shoulder girdle stiffness and morning stiffness but not true myopathic weakness and is not linked to anti-Jo-1. SLE would present with a broader systemic pattern and different antibodies.