Classification by predominant involvement
Depending on the extent of pulmonary tissue involvement in the pathological process, three main groups of disorders are distinguished:
- Primary pulmonary vasculitides. These are systemic vasculitides in which the lungs serve as the primary target. They include granulomatosis with polyangiitis (Wegener granulomatosis), microscopic polyangiitis, and Churg-Strauss syndrome (eosinophilic granulomatosis with polyangiitis).
- Systemic vasculitides with potential pulmonary involvement. This group includes polyarteritis nodosa, microscopic polyangiitis, and Takayasu arteritis. Note: if a patient presents with simultaneous vascular lesions of the lungs and kidneys, clinical practice uses the term "pulmonary-renal syndromes".
- Secondary vasculitides. These develop as a complication of other conditions. They can occur against the background of systemic diseases (systemic lupus erythematosus, sarcoidosis, Langerhans cell histiocytosis, lymphoproliferative disorders), severe infections, or following organ transplantation.
Pathogenesis
The development of pulmonary vasculitis is based on two main immune mechanisms:
- Immune complex-mediated. Immune complexes form in the bloodstream and subsequently deposit in the vessel walls. This leads to complement system activation, massive leukocyte recruitment, and the initiation of an inflammatory reaction. This mechanism is most characteristic of systemic lupus erythematosus (SLE), polyarteritis nodosa, and other systemic connective tissue diseases.
- ANCA-associated. Inflammation of the vessel wall is directly linked to the production of anti-neutrophil cytoplasmic antibodies (ANCAs).
Morphological triad
The classic pathomorphological picture of pulmonary vasculitis consists of three mandatory elements:
- Necrotic granulomas. Irregular in shape. Their cellular composition includes neutrophils, lymphocytes, plasma cells, macrophages, eosinophils, and multinucleated giant histiocytes. Around the zone of necrosis, histiocytes may arrange into characteristic palisading structures. Important for differential diagnosis: sarcoid-like granulomas are not characteristic of this pathology.
- Vasculitis. Pronounced destructive character affecting arteries, veins, and capillaries. Polymorphonuclear cell infiltration, thrombosis, and fibrinoid necrosis are found within the wall of the affected vessel.
- Foci of necrosis. Localized both within the granulomas themselves and in the surrounding lung tissue. Externally, they resemble a "geographic map" and have a basophilic staining due to the accumulation of destroyed cell nuclei. Necrosis forms via two mechanisms:
- Heterolysis: neutrophil activation leads to the formation of microabscess-like structures.
- Ischemia: ischemic pulmonary infarctions occur. This is caused by the blockade of blood supply through vascular shunts from bronchial artery branches against the background of widespread vasculitis. Similar ischemic necrosis may also be found in the brain.
Concomitant morphological changes
In addition to the classic triad, additional pathological processes are frequently detected in the lung tissue. These include:
- Alveolar hemorrhages.
- Interstitial fibrosis.
- Organizing pneumonia (OP) and bronchiolitis obliterans organizing pneumonia (BOOP).
- Lipoid pneumonia and lymphoid hyperplasia.
- Bronchial tree lesions: chronic or follicular bronchiolitis, bronchial stenosis, and bronchocentric granulomatosis.
Briefly: answers to topical questions
Which diseases cause pulmonary-renal syndrome?
Pulmonary-renal syndrome develops with simultaneous involvement of the lungs and kidneys. Diseases confirmed by sources to feature combined lung and kidney involvement include:
- Microscopic polyangiitis — belongs to pulmonary-renal syndrome; kidney and lung pathology is detected in virtually all patients.
- Wegener granulomatosis — affects the upper respiratory tract, lungs, and kidneys; necrotizing glomerulonephritis frequently develops.
- Goodpasture syndrome — listed among diseases with pulmonary involvement and among the causes of rapidly progressive glomerulonephritis.
What types of ANCA are distinguished in pulmonary vasculitis, and what are their target enzymes?
In pulmonary vasculitis, two main types of anti-neutrophil cytoplasmic antibodies (ANCAs) are distinguished, targeting enzymes found in the primary granules of neutrophils and monocytes:
- Cytoplasmic ANCA (cANCA) — bind to the enzyme proteinase-3. They are characteristic of Wegener granulomatosis.
- Perinuclear ANCA (pANCA) — directed against the enzyme myeloperoxidase. These antibodies are typical of microscopic polyangiitis and Churg-Strauss syndrome.
How does Wegener granulomatosis differ morphologically from Churg-Strauss syndrome?
The morphological differences between Wegener granulomatosis and Churg-Strauss syndrome lie in the cellular composition of the granulomas, the nature of the inflammatory infiltration, and the frequency of renal involvement.
| Sign | Granulomatosis with Polyangiitis | Churg-Strauss syndrome |
|---|---|---|
| Granuloma composition | Lymphoid cells, monocytes, macrophages, fibroblasts | Histiocytes, multinucleated cells, eosinophils |
| Specific sign | Presence of neutrophilic leukocytes | Eosinophilic cellular infiltration, granulomas in the demarcation zone of infarctions |
| Renal involvement | Necrotizing glomerulonephritis frequently develops | Kidneys are extremely rarely affected |
What caliber of blood vessels is affected in microscopic polyangiitis?
In microscopic polyangiitis, small-caliber vessels are predominantly affected. The inflammatory process spreads to the following elements of the vascular bed:
- Arterioles;
- Capillaries (including glomerular capillaries);
- Venules.
In addition, small- and medium-sized arteries may be involved in the pathological process.
For quick memorization of the morphological triad, use the rule "GVN" (in Russian): G — Granulomas (necrotic), V — Vasculitis (destructive), N — Necrosis (geographic map-like).
Class and exam questions
Which granulomas are not characteristic of pulmonary vasculitides?
Sarcoid-like granulomas are not characteristic. Vasculitis is typically characterized by irregular necrotic granulomas in which histiocytes form palisading structures around the zone of necrosis.
What type of necrosis develops in the vessel wall in pulmonary vasculitis?
Fibrinoid necrosis develops in the vessel wall, accompanied by thrombosis and pronounced polymorphonuclear cell infiltration.
What is the cause of ischemic lung infarctions in vasculitis?
Ischemia arises due to widespread involvement of the pulmonary and bronchial arteries. This leads to the blockade of blood supply via vascular shunts, which triggers tissue infarction.
What does the term "pulmonary-renal syndrome" mean?
This clinical concept is applied in cases where systemic vasculitis simultaneously affects the pulmonary and renal vasculature.
What else to study on this topic
- Wegener's granulomatosis (granulomatosis with polyangiitis): lesion specifics
- Churg-Strauss syndrome: the role of eosinophils in pathogenesis
- Microscopic polyarteritis and polyangiitis: morphological differences
- Mechanisms of ANCA-associated vasculitis development
- Bronchocentric granulomatosis and bronchiolitis obliterans
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