## Clinical Context This patient presents with dermatomyositis (DM) — evidenced by proximal muscle weakness, elevated CK, and anti-Jo-1 antibody positivity — in the setting of a lung mass on imaging. ## Key Pathophysiology **Key Point:** Dermatomyositis is a paraneoplastic syndrome associated with underlying malignancy in 10–50% of adult cases, particularly lung cancer. The presence of a lung mass on imaging in a patient with newly diagnosed DM is a red flag for occult malignancy. ## Management Algorithm ```mermaid flowchart TD A[DM with lung mass on imaging] --> B{Malignancy suspected?} B -->|Yes| C[Urgent oncology referral + lung biopsy] C --> D[Concurrent: Start corticosteroids] D --> E[Treat both paraneoplastic syndrome and cancer] B -->|No| F[Treat DM with immunosuppression] ``` ## Rationale for Correct Answer 1. **Concurrent dual management**: Corticosteroids address the inflammatory myositis, while urgent lung cancer staging and biopsy confirm malignancy and guide oncologic therapy. 2. **Timing is critical**: Paraneoplastic DM often improves with treatment of the underlying cancer; delaying cancer diagnosis worsens prognosis. 3. **Anti-Jo-1 positivity** is associated with interstitial lung disease and is a strong predictor of malignancy-associated myositis. ## High-Yield Facts **High-Yield:** In any adult presenting with dermatomyositis, particularly with anti-synthetase antibodies (Jo-1, PL-7, EJ), a thorough malignancy screen (CT chest/abdomen, age-appropriate cancer screening) is mandatory before attributing symptoms solely to autoimmunity. **Clinical Pearl:** The presence of a lung mass on imaging in a DM patient is NOT incidental — it must be biopsied and staged urgently, as treatment of the underlying cancer often leads to remission of myositis.
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