Rheumatoid arthritis (RA) can have significant effects on the lungs, leading to a variety of pulmonary diseases. These lung complications are often underrecognized but can be severe. The main lung diseases associated with RA include:

1. Interstitial Lung Disease (ILD)

• The most common and serious pulmonary manifestation of RA.
• Presents as progressive dyspnea and dry cough.
• Usual Interstitial Pneumonia (UIP) and Non-Specific Interstitial Pneumonia (NSIP) are the most common histologic patterns.
• Risk factors: Male sex, smoking, high RA disease activity, and presence of rheumatoid factor (RF) or anti-CCP antibodies.

2. Rheumatoid Nodules in the Lungs

• Can be single or multiple and often appear in the subpleural or apical regions.
• Typically asymptomatic, but may cavitate and lead to infections or pneumothorax.

3. Pleural Disease

• Pleural effusion: Often exudative with low glucose and low pH.
• Can be associated with chronic pleuritis.

4. Airway Disease

• Bronchiolitis Obliterans (BO): Leads to obstructive lung disease due to small airway inflammation.
• Follicular bronchiolitis: Associated with chronic cough and mild airway obstruction.
• Cricoarytenoid arthritis: Can cause hoarseness, stridor, or airway obstruction.

5. Pulmonary Hypertension

• Can develop secondary to ILD or vasculitis.
• May present with exertional dyspnea and fatigue.

6. Drug-Induced Lung Disease

• Methotrexate (MTX)-induced pneumonitis: Presents with acute onset of fever, cough, and hypoxia.
• Leflunomide, TNF inhibitors, and JAK inhibitors can also contribute to lung complications.

7. Increased Risk of Infections

• Patients on immunosuppressive therapy (e.g., MTX, biologics) are at higher risk for opportunistic infections, including Pneumocystis jirovecii pneumonia (PJP), tuberculosis (TB), and bacterial pneumonia.

Imaging and Diagnosis

• HRCT (High-Resolution CT): Gold standard for detecting RA-associated ILD.
• Pulmonary Function Tests (PFTs):
  • ILD: Restrictive pattern with ↓ DLCO.
  • Airway disease: Obstructive or mixed pattern.

Management

• RA-ILD: Treated with glucocorticoids, immunosuppressants (e.g., mycophenolate mofetil, rituximab), or antifibrotics (nintedanib, pirfenidone).
• Pleural effusions: May require thoracentesis or pleurodesis.
• Methotrexate-induced lung disease: Discontinuation of the drug is necessary.
• Infections: Prompt treatment with antibiotics or antifungals.
• Pulmonary hypertension: Managed with vasodilators (e.g., PDE-5 inhibitors, endothelin receptor antagonists).

eature	Bronchiolitis Obliterans (BO)	Follicular Bronchiolitis (FB)
Cause	Fibrosis of small airways	Lymphoid hyperplasia around bronchioles
Pathology	Fibrotic narrowing and obliteration of bronchioles	Reactive lymphoid proliferation
Clinical Presentation	Progressive dyspnea, dry cough	Chronic cough, mild dyspnea
HRCT Findings	Mosaic attenuation, air trapping, bronchial thickening	Centrilobular nodules, tree-in-bud pattern
PFTs	Obstructive pattern (↓ FEV1/FVC, ↑ RV/TLC)	Mixed restrictive/obstructive pattern
Treatment	Supportive, no effective cure, poor response to steroids	May respond to steroids/immunosuppressants
Prognosis	Poor, irreversible airway damage	Better, potentially reversible

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Summary

• BO is a fibrotic, irreversible disease leading to progressive airway obstruction.
• FB is a lymphoid hyperplasia condition that is potentially reversible with treatment.