A 52-year-old man with established rheumatoid arthritis (RF-positive, anti-CCP-positive) on methotrexate presents with new-onset dyspnea and bilateral interstitial infiltrates on chest X-ray. His rheumatologist suspects rheumatoid lung disease. Which investigation is most appropriate to confirm pulmonary involvement and assess disease severity?

Explanation

## Diagnosis of Rheumatoid Lung Disease **Key Point:** High-resolution computed tomography (HRCT) of the chest is the gold standard investigation for detecting and characterizing pulmonary manifestations of rheumatoid arthritis, including usual interstitial pneumonia (UIP), nonspecific interstitial pneumonia (NSIP), and organizing pneumonia. ### Pulmonary Manifestations of RA and Diagnostic Approach | Pulmonary Manifestation | Frequency | HRCT Pattern | Clinical Significance | |-------------------------|-----------|--------------|----------------------| | Interstitial lung disease (ILD) | 10–30% | UIP, NSIP, OP | Most common; associated with poor prognosis | | Rheumatoid nodules | 20–30% | Nodular opacities | Often asymptomatic; cavitation possible | | Pleural disease | 5–10% | Pleural thickening/effusion | Usually mild; may precede arthritis | | Bronchiectasis | 5–15% | Bronchial dilation | Associated with increased mortality | | Bronchiolitis obliterans | Rare | Mosaic perfusion | Rapidly progressive; poor prognosis | **High-Yield:** HRCT can detect subclinical ILD in up to 30% of RA patients without respiratory symptoms. Early detection allows intervention to prevent progression to pulmonary fibrosis and respiratory failure. **Clinical Pearl:** Methotrexate, commonly used to treat RA, can itself cause drug-induced pulmonary toxicity (hypersensitivity pneumonitis or pulmonary fibrosis). HRCT helps differentiate methotrexate-induced lung disease from RA-related ILD based on pattern and distribution. **Warning:** ~~Serum biomarkers~~ like SP-A and KL-6 are non-specific and elevated in various ILDs; they cannot confirm RA-related lung disease or replace imaging. ~~Expiratory chest X-rays~~ are used for air-trapping assessment in small airway disease but lack sensitivity for early ILD detection. ~~ANA~~ is not specific for RA-related pulmonary involvement and may reflect overlap with other autoimmune diseases. ### Diagnostic Algorithm for RA with Respiratory Symptoms ```mermaid flowchart TD A[RA patient with dyspnea/infiltrates]:::outcome --> B{Clinical suspicion<br/>for RA-ILD?}:::decision B -->|Yes| C[HRCT chest]:::action B -->|No| D[Chest X-ray only]:::action C --> E{Pattern identified?}:::decision E -->|UIP/NSIP/OP| F[RA-ILD confirmed]:::outcome E -->|Nodules| G[Rheumatoid nodules]:::outcome E -->|Mosaic pattern| H[Bronchiolitis obliterans]:::urgent F --> I[Review DMARD regimen<br/>Consider antifibrotic therapy]:::action H --> J[Urgent pulmonology referral<br/>High mortality risk]:::urgent ``` [cite:Harrison 21e Ch 297]