A 52-year-old woman presents with progressive proximal muscle weakness and a violaceous rash over her knuckles and elbows. Examination reveals the lesion marked **B** in the diagram — flat-topped, scaly papules over the extensor surfaces of her metacarpophalangeal and interphalangeal joints. Serum CK is elevated at 3200 U/L. Myositis-specific antibody panel returns positive for anti-TIF-1γ. Which of the following is the MOST important next step in her management?

## Why "Initiate prednisolone 1 mg/kg/day and refer for comprehensive age-appropriate cancer screening" is right The structure marked **B** — Gottron papules over MCP/PIP joints — is a pathognomonic cutaneous feature of dermatomyositis (DM). Combined with proximal muscle weakness, elevated CK, and anti-TIF-1γ positivity, this confirms DM. Critically, anti-TIF-1γ antibodies are associated with paraneoplastic DM in >50% of cases (Harrison 21e Ch 358). The clinical anchor is that TIF-1γ positivity mandates extensive age-appropriate cancer screening (CT chest/abdomen/pelvis, age-appropriate malignancy screen, repeat at 1 and 2 years) ALONGSIDE initiation of systemic corticosteroids (prednisolone 1 mg/kg/day, max 60–80 mg) as first-line therapy. This dual approach — immunosuppression + cancer surveillance — is essential because 15–30% of adult-onset DM is paraneoplastic, with TIF-1γ conferring the highest risk. ## Why each distractor is wrong - **Start methotrexate monotherapy without cancer workup**: Methotrexate is a steroid-sparing agent used AFTER corticosteroid initiation or as adjunctive therapy, not monotherapy. More critically, omitting cancer screening in a TIF-1γ-positive patient is a dangerous oversight — paraneoplastic DM requires mandatory malignancy workup at diagnosis per EULAR/ACR guidelines. - **Perform muscle biopsy immediately to confirm diagnosis before any systemic therapy**: While muscle biopsy (showing perifascicular atrophy, perivascular inflammation, complement deposition) is diagnostic, the clinical presentation (Gottron papules + proximal weakness + elevated CK + positive MSA) is sufficiently characteristic to initiate treatment without delay. Delaying corticosteroids risks progressive muscle damage and aspiration risk (dysphagia is a key DM complication). - **Administer intravenous immunoglobulin (IVIG) as first-line therapy**: IVIG is reserved for severe/refractory disease, dysphagia, pregnancy, or severe ILD — not as first-line monotherapy. Corticosteroids remain the gold standard initial therapy for DM. **High-Yield:** Anti-TIF-1γ positivity in dermatomyositis = paraneoplastic disease until proven otherwise; mandatory comprehensive cancer screening at diagnosis and repeat surveillance at 1 and 2 years, especially in older-onset DM. [cite: Harrison 21e Ch 358 — Dermatomyositis pathogenesis, autoantibody subtypes, paraneoplastic associations, and management]