Lung involvement in rheumatoid arthritis

Interstitial lung diseases in RA

Among interstitial lung diseases (ILD) associated with rheumatoid arthritis, two main histological and radiological patterns dominate:

1. Usual interstitial pneumonia (UIP / UIP). This is the most frequent type of involvement. On high-resolution computed tomography (HRCT / HRCT), the picture is completely identical to the idiopathic form of UIP. Peripheral reticular changes and the classic honeycombing pattern are defined in the lungs. At the same time, the prognosis for UIP in RA is considered somewhat more favorable than in the isolated idiopathic form.
2. Non-specific interstitial pneumonia (NSIP / NSIP). It is significantly less common than UIP (unlike systemic sclerosis or Sjögren's syndrome, where NSIP leads).

In some cases, acute exacerbations of ILD occur. Histologically, they manifest as diffuse alveolar damage (DAD / DAD), and radiologically resemble acute respiratory distress syndrome (ARDS / ARDS). In such situations, it is extremely difficult to perform a differential diagnosis with pulmonary edema or the addition of opportunistic infections.

Bronchial tree pathology

In patients with rheumatoid arthritis, not only the interstitium but also the airways are frequently affected. In almost 30% of patients, mild cylindrical bronchiectasis is detected on HRCT. In addition, small airway disease is characteristic:

• Obliterative bronchiolitis (Obliterative bronchiolitis). The disease can develop either without treatment or during therapy with penicillamine or gold salts. On HRCT, this constrictive process manifests as a mosaic attenuation pattern: areas of decreased lung attenuation with a reduced vascular pattern and pronounced air trapping are visible. The condition can lead to severe respiratory failure requiring lung transplantation.
• Follicular bronchiolitis. It belongs to lymphoproliferative processes. It manifests as diffuse peribronchiolar proliferation of lymphoid follicles. Clinically, it presents with progressive dyspnea in young or middle age. On HRCT, bilateral centrilobular nodules (1–12 mm), ground-glass opacity areas, and less commonly, a tree-in-bud pattern are most often visible.

Rheumatoid nodules and pleuritis

Necrobiotic pulmonary nodules are a rare but very specific manifestation of rheumatoid arthritis, which is almost always combined with the presence of similar subcutaneous formations.

The size of the nodules varies from a few millimeters to 4 centimeters. They can be single or multiple, have clear contours, and have a high tendency for cavity formation (cavitation). Contrast-enhanced imaging reveals a hypodense necrotic core.

Clinically important features of nodules:

• If a nodule is located subpleurally, its destruction can provoke a pneumothorax.
• They actively take up the radiopharmaceutical (FDG) on PET-CT. This feature must categorically not be confused with metastatic lung lesions.
• The course is usually asymptomatic, and the appearance or disappearance of nodules is undulating in nature and correlates with pleural changes.

Pleural involvement in RA is very common, usually in the form of pleural effusion.

Differential diagnosis with other collagenoses

Lung involvement in RA must be distinguished from other systemic connective tissue diseases. A brief comparison of typical CT findings is given below:

Briefly: answers to topical questions

Class and exam questions

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