Classification and pathogenesis
The size of the affected blood vessels is a key criterion determining the clinical and radiological picture of vasculitis. The pulmonary interstitium is most frequently involved in ANCA-associated vasculitis, which is characterized by the circulation of antineutrophil cytoplasmic antibodies (ANCA):
- Granulomatosis with polyangiitis (GPA, formerly Wegener's granulomatosis): associated with cytoplasmic ANCA (c-ANCA).
- Eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-Strauss syndrome): associated with perinuclear ANCA (p-ANCA).
- Microscopic polyangiitis (MPA): also characterized by the expression of p-ANCA.
Eosinophilic granulomatosis with polyangiitis (EGPA)
The disease manifests as necrotizing vasculitis and extravascular granulomatous inflammation with massive tissue eosinophilic infiltration (sometimes presenting similarly to organizing pneumonia). The clinical picture is dominated by fever, blood eosinophilia, peripheral neuropathy, and bronchial asthma (its presence at any point in the disease is mandatory for diagnosis).
Radiological methods are often uninformative: changes are absent in 25% of patients, and the diagnostic accuracy of HRCT (HRCT) does not exceed 50%. The pattern is non-specific and reflects eosinophilic infiltration.
Classic HRCT patterns:
- Areas of decreased attenuation in the form of ground-glass opacities (ground-glass opacities) and consolidation zones.
- Small cavitating lesions (with decay cavities) and centrilobular nodules.
- Interlobular septal thickening (often secondary, due to cardiac involvement).
- Pleural or pericardial effusion.
- Bronchial abnormalities typical of asthma.
Microscopic polyangiitis (MPA)
MPA is a systemic non-granulomatous small-vessel vasculitis. Renal manifestations include segmental necrotizing glomerulonephritis, whereas in the lungs, the most frequent and formidable sign (10–30% of cases) is diffuse alveolar hemorrhage (DAH).
Pulmonary edema occurs in 6% of cases, and pleural effusion in 15% of patients. The development of pulmonary fibrosis is atypical, but if it occurs, it sharply worsens the prognosis.
On a chest X-ray (CXR), the lungs may appear intact or exhibit diffuse parenchymal opacities. Typical HRCT findings include:
- Subsolid centrilobular nodules with unclear, blurred margins (faint margins).
- Focal areas of ground-glass opacity (resulting from alveolar hemorrhage).
Differential diagnosis: drug-induced lung injury
Although drug toxicodermias and gastroenteropathies are more common, the pneumotoxicity of medications (especially targeted therapy and checkpoint inhibitors) is steadily increasing. Smokers with chronic lung injury have a higher risk of such reactions.
Manifestations are heterogeneous: ranging from allergy and idiosyncrasy to direct pharmacological action. This is always a diagnosis of exclusion (infections, cardiogenic edema, and systemic diseases must be ruled out). Early-stage radiography may be normal, and histology does not always correlate with HRCT (biopsy is rarely performed). Most drugs can cause multiple histological patterns simultaneously:
- Diffuse alveolar damage (DAD): frequently caused by chemotherapy drugs (bleomycin, busulfan, cyclophosphamide, carmustine), amiodarone, gold salts, and targeted therapy (VEGF/EGFR inhibitors).
- Diffuse alveolar hemorrhage (DAH): anticoagulants, amphotericin B, penicillamine, cytosine arabinoside.
- Interstitial pneumonia: amiodarone, methotrexate, nitrofurantoin, targeted drugs (PD-1/PD-L1, mTOR, ALK, HER2, anti-CD20 inhibitors).
- Organizing pneumonia: sulfasalazine, methotrexate, bleomycin.
- Eosinophilic pneumonia: NSAIDs, penicillamine, nitrofurantoin, PAS.
Briefly: answers to topical questions
What vascular manifestations are characteristic of microscopic polyangiitis?
Microscopic polyangiitis is characterized by non-granulomatous systemic small-vessel vasculitis. Renal involvement presents as segmental necrotizing glomerulonephritis, and in severe cases, as rapidly progressive glomerulonephritis with prominent necrosis, fibrin deposition, and epithelial crescent formation. Diffuse alveolar hemorrhage is the most common pulmonary manifestation, occurring in 10–30% of cases.
GPA — c-ANCA (Granulomatosis — Center). EGPA and MPA — p-ANCA (Periphery).
Class and exam questions
What is the main diagnostic criterion for EGPA?
A mandatory condition for diagnosing eosinophilic granulomatosis with polyangiitis is the presence of bronchial asthma in the patient at any time during the disease course.
How effective is HRCT in EGPA?
HRCT is of low diagnostic utility: its diagnostic accuracy is below 50%, and in a quarter of patients, lung changes are completely absent on scans.
Which pulmonary complication is typical for microscopic polyangiitis?
The most frequent pulmonary manifestation (up to 30% of cases) is diffuse alveolar hemorrhage, which presents on CT as ground-glass opacities and subsolid nodules.
Why are drug-induced lung injuries considered a diagnosis of exclusion?
Because their clinical and radiological patterns are completely non-specific. First, the physician must rule out infectious processes, cardiogenic edema, and systemic connective tissue diseases.
What else to study on this topic
- Pathomorphology of air space involvement in GPA
- Mechanisms of cavitating lesion development in systemic vasculitis
- The specifics of targeted therapy in the development of interstitial pneumonias
- Differential diagnosis of diffuse alveolar hemorrhage
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