A 38-year-old woman with a 4-year history of seropositive RA (RF 220 IU/mL, anti-CCP 110 U/mL) well-controlled on methotrexate 15 mg weekly presents with a 3-week history of progressive dyspnea on exertion and a dry cough. She denies fever or chest pain. Chest X-ray shows bilateral interstitial infiltrates. High-resolution CT chest confirms usual interstitial pneumonia (UIP) pattern. PFTs show FVC 65% predicted, DLCO 48% predicted. What is the most likely diagnosis and the most appropriate next step in management?

Explanation

## RA-Associated Interstitial Lung Disease (RA-ILD) ### Clinical Presentation & Diagnosis **Key Point:** RA-ILD is a common extra-articular manifestation affecting 5–10% of RA patients clinically, but subclinical ILD is present in up to 40% on HRCT. UIP pattern on HRCT is the most common radiologic finding and indicates poor prognosis. ### Why This Is RA-ILD, Not MTX Toxicity | Feature | MTX-Induced Pneumonitis | RA-ILD (UIP Pattern) | |---------|------------------------|----------------------| | **Timeline** | Acute onset, weeks to months; reversible | Insidious, progressive over months–years; progressive | | **HRCT pattern** | Hypersensitivity pneumonitis (ground-glass, nodules) | UIP (reticular, honeycombing, traction bronchiectasis) | | **Disease course** | Improves with MTX discontinuation | Progressive despite MTX discontinuation | | **DLCO** | Mild reduction | Marked reduction (48% here = severe) | | **Prognosis** | Good if caught early | Poor; median survival 3–5 years untreated | | **Management** | Stop MTX, corticosteroids | Continue MTX, add antifibrotic ± immunosuppression | **Clinical Pearl:** This patient's UIP pattern on HRCT is pathognomonic for RA-ILD, NOT MTX toxicity. MTX-induced pneumonitis typically presents with acute hypersensitivity features (ground-glass opacities, nodules) and resolves after drug withdrawal. ### Management of RA-ILD with UIP Pattern ```mermaid flowchart TD A[RA-ILD confirmed on HRCT]:::outcome --> B{Assess disease severity}:::decision B -->|Mild-moderate FVC >50%| C[Continue MTX + add antifibrotic]:::action B -->|Severe FVC <50% or rapid decline| D[Consider immunosuppression ± antifibrotic]:::action C --> E[Pirfenidone or Nintedanib]:::action D --> F[Corticosteroids + MTX + antifibrotic]:::action E --> G[Monitor PFTs every 3 months]:::action F --> G ``` **High-Yield:** Antifibrotic agents (pirfenidone, nintedanib) are now standard of care for RA-ILD with UIP pattern because they slow FVC decline by ~50% and improve survival. ### Why Continue MTX? - MTX is NOT contraindicated in RA-ILD; in fact, continuing MTX while adding antifibrotics is the preferred approach - Stopping MTX and starting high-dose corticosteroids alone is outdated and less effective - Corticosteroids may be added if there is evidence of active inflammation (elevated CRP, acute exacerbation), but antifibrotics are the cornerstone **Warning:** High-dose corticosteroids monotherapy for RA-ILD with UIP pattern is associated with worse outcomes and increased infection risk; they should not be used as monotherapy. ### Monitoring & Follow-up - PFTs (FVC, DLCO) every 3 months for first year, then every 6 months - HRCT annually or if clinical deterioration - Assess for acute exacerbation (acute dyspnea, hypoxemia, new infiltrates) — treat with high-dose corticosteroids + immunosuppression - Screen for lung cancer (increased risk in RA-ILD) [cite:Harrison 21e Ch 313; Lancet 2021 RA-ILD consensus]