Rheumatoid Arthritis-Associated Interstitial Lung Disease (RA-ILD)

1. INTRODUCTION AND EPIDEMIOLOGY

2. RISK FACTORS

3. PULMONARY MANIFESTATIONS - OVERVIEW

4. INTERSTITIAL LUNG DISEASE (DETAILED)

4a. Histopathological Patterns

• UIP (Usual Interstitial Pneumonia) - most common pattern in RA-ILD
• NSIP (Nonspecific Interstitial Pneumonia) - second most common

• UIP is associated with worse outcome than NSIP in RA
• UIP has a worse outcome in RA than in other CTDs
• RA patients with UIP + HRCT similar to classical IPF have average outcomes similar to IPF; however, ~25% of such patients have a good long-term outcome
• Minor pulmonary fibrosis found in 60% of open-lung biopsies in RA volunteers (even without overt ILD)

4b. Clinical Features of RA-ILD

• Symptoms: Dry cough, exertional dyspnea, chest pain
• Physical signs: Bibasilar Velcro crackles, digital clubbing, signs of cor pulmonale (if pulmonary hypertension develops)
• Presence of RA-ILD (approximately 10% of symptomatic patients) is associated with increased mortality

5. PLEURAL DISEASE

• Postmortem incidence: 40%; clinically apparent: 5%
• More common in men
• Occurs most during active articular disease
• In 20% of patients, pleural disease precedes articular manifestations

6. NECROBIOTIC (RHEUMATOID) NODULES

• Radiographically visible in only 1% of RA patients
• More common in men, smokers, high RF titers, subcutaneous nodules
• Distribution: Subpleural, upper- and midzone predilection
• Size: Variable, up to 7 cm; approximately 50% cavitate (due to proteolytic enzymes)
• Features: Single or multiple; spontaneous resolution and recurrence expected; usually asymptomatic
• Cavitation complications: Pneumothorax, pleural effusion, hemoptysis
• Key differentiation: Must be distinguished from malignant or infectious granulomatous disease (particularly important given increased lung cancer risk in RA)

7. AIRWAY DISEASE

Obliterative Bronchiolitis (BO)

• Produces constrictive bronchiolitis with severe airflow obstruction
• Chest X-ray: Normal or hyperinflation
• HRCT: Mosaic perfusion (areas of increased and decreased attenuation)
• Bronchiectasis and bronchial wall thickening common on CT
• Prognosis: Poor - regression virtually never seen

Follicular Bronchiolitis

• Dense lymphocytic and plasma cell infiltration around terminal/respiratory bronchioles
• Symptoms: Cough and dyspnea
• HRCT: Centrilobular nodules and bronchiectasis (in up to 33% of RA patients)
• Physiology: Gas exchange abnormalities dominate (rather than airflow limitation)
• Treatment: Corticosteroids with variable results

Cricoarytenoid Joint Involvement (Upper Airway)

• Prevalence approaches 50% on CT screening (mostly asymptomatic)
• Symptoms: Sore throat, hoarseness, globus sensation, inspiratory difficulty, stridor
• Important anesthetic consideration: May complicate endotracheal intubation; must be considered before general anesthesia

8. PULMONARY VASCULAR DISEASE

• Least common pleuropulmonary complication
• Associated with Raynaud phenomenon
• CXR: Normal lung fields + enlarged pulmonary arteries
• PFT: Isolated reduction of DLCO + hypoxemia
• Pulmonary capillaritis causing diffuse alveolar hemorrhage (DAH) - very rare; may have p-ANCA (anti-MPO)
• Treatment: IV methylprednisolone + cyclophosphamide; rituximab for remission induction

9. PULMONARY FUNCTION TESTS (PFTs)

• DLCO reduction: Found in 40% of unselected RA patients (marker of occult interstitial fibrosis)
• Restrictive defect: Seen in UIP, NSIP, OP, LIP - reduced TLC, VC, compliance
• Obstructive defect: Bronchiectasis or BO
• Flow-volume loops: Variable extrathoracic obstruction in cricoarytenoid arthritis
• Airflow obstruction was predominant in some cohorts
• Serial FVC monitoring is essential for tracking disease progression

10. RADIOLOGICAL FEATURES

Chest X-Ray:

• ILD visible in only 1-5% of unselected RA patients on CXR
• Symmetrical basal interstitial opacification in limited disease
• Coarse diffuse reticular abnormalities in extensive disease
• UIP: Lower zone and peripheral reticulonodular infiltrates progressing to honeycomb lung at lung bases
• OP: Lower-zone mixed alveolar-interstitial infiltrates (patchy/localized)

HRCT Patterns:

• UIP: Predominantly basal subpleural honeycomb change + traction bronchiectasis, often with little ground-glass
• NSIP: Homogeneous ground-glass opacity + reticulation + traction bronchiectasis with peribronchiovascular distribution
• OP: Patchy bilateral air space consolidation, often subpleural or bronchovascular distribution; small nodules, small pleural effusions
• BO: "Mosaic perfusion" - patchy areas of reduced lung density with reduced vessel caliber
• FB: Centrilobular micronodular opacities and peripheral branching structures
• Rheumatoid nodules: Discrete, often multiple, ≤7 cm; in Caplan syndrome, appear in crops, grow rapidly, may cavitate

11. BRONCHOALVEOLAR LAVAGE (BAL) FINDINGS

12. DRUG-INDUCED LUNG DISEASE IN RA

Methotrexate Pneumonitis:

• Occurs in 1-18% of RA patients on methotrexate (low weekly doses: 10-20 mg)
• Mortality: 15-20%
• Onset: Often subacute (up to 2 months); 50% diagnosed within 4 months of starting
• Clinical: Acute cough, fever, dyspnea + mixed alveolar-interstitial infiltrates
• BAL: Lymphocytosis (rule out infection)
• Histology: NSIP, OP, granuloma formation (resembles hypersensitivity pneumonitis)
• Management: Immediate drug withdrawal + early steroids (IV methylprednisolone for severe cases); do NOT retreat

Gold Therapy:

• Dyspnea and cough begin 4-6 weeks after initiation
• BAL: Lymphocyte predominance
• Occasional upper-zone mixed alveolar-interstitial infiltrates
• Withdrawal + corticosteroids in severe cases

Anti-TNF Agents (etanercept, infliximab):

• Conflicting data on whether ILD association is causal or temporal
• Major concern: Reactivation of tuberculosis, atypical mycobacteria, fungi
• Some series suggest temporal association with new ILD development

Leflunomide:

• Associated with pulmonary rheumatoid nodules and interstitial disease

13. ACUTE EXACERBATIONS OF RA-ILD

• Less prevalent in CTD-ILD than in IPF, but more common in RA than in other CTDs
• Features: Worsening dyspnea over 2-4 weeks + new ground-glass opacities on HRCT + absence of infection or other overt cause
• High early mortality
• Pathology: Diffuse alveolar damage (DAD) superimposed on background ILD
• No proven therapy; high-dose corticosteroids are usually given

14. TREATMENT OF RA-ILD

General Approach:

• Optimal treatment is not established; highly individualized based on the histologic/radiologic subtype
• Lung function improvement is possible but a more realistic goal is stabilization

Treatment by Pattern:

Pharmacological Agents:

1. Corticosteroids - First-line therapy; caution with UIP pattern (similar toxicity risks as in IPF)
2. Rituximab - May slow physiologic decline; used for vasculitis and respiratory muscle dysfunction; role in ILD uncertain
3. Tocilizumab - Appears to slow progression of lung function decline
4. Abatacept - Associated with stabilization of lung function in some patients
5. Methotrexate/DMARDs - Treatment of underlying RA; however, methotrexate itself can cause ILD
6. Nintedanib - In patients with progressive fibrosing ILD including RA-ILD with UIP pattern over the preceding 24 months, nintedanib reduces the annual rate of FVC decline vs. placebo (IN-BUILD trial) - Fishman's, p. 1030
7. Pirfenidone - Under evaluation (TRAIL study); not yet approved for RA-ILD

15. PROGNOSIS

• RA-ILD with UIP pattern has outcomes similar to IPF
• However, approximately 25% of RA-UIP patients have good long-term outcomes (distinguishing from IPF)
• RA-ILD is associated with increased mortality in symptomatic patients
• Extent of ILD on CT correlates with lower FVC at baseline and predicts progression
• BAL neutrophilia + eosinophilia = poor prognostic sign (underlying UIP)
• DLCO is the most sensitive early physiologic marker

SUMMARY TABLE FOR QUICK REVISION

• Fishman's Pulmonary Diseases and Disorders, 2-Volume Set - Chapter 58 (Connective Tissue Diseases and the Lung), pp. 1025-1030
• Murray & Nadel's Textbook of Respiratory Medicine, 2-Volume - Chapter 92 (Connective Tissue Diseases), pp. 2091-2094This is a complete, exam-ready 15-mark answer drawn exclusively from Fishman's Pulmonary Diseases and Disorders (Chapter 58, pp. 1025-1030) and Murray & Nadel's Textbook of Respiratory Medicine (Chapter 92, pp. 2091-2094). Here are the high-yield points to not miss:

1. Male predominance (3:1) - opposite to most other CTD-ILDs which are female-predominant
2. Pleural glucose <30 mg/dL - virtually pathognomonic; only RA or empyema gives this
3. ILD can precede arthritis by months to years - in up to 20% of patients
4. UIP in RA = worse prognosis than NSIP, but still better than idiopathic IPF in 25% of patients
5. MUC5B variant - the key genetic predisposition for RA-UIP specifically
6. Nintedanib is the only approved-level evidence agent for progressive fibrosing RA-ILD (IN-BUILD trial)
7. BAL neutrophil + eosinophil predominance = poor prognostic marker (underlying UIP)
8. Caplan syndrome = RA + pneumoconiosis + upper lobe nodules in crops
9. Acute exacerbations are more common in RA-ILD than in other CTD-ILDs, and carry high early mortality
10. High-dose corticosteroids should be used with caution when CT looks like IPF - this is the same caution as in pure IPF management