Classification by caliber and localization
Systemic vasculitides are classified according to the caliber of the affected vessels and their anatomical classification:
- Large vessels: aortitis (aorta and its branches).
- Medium and small vessels: arteritis, arteriolitis, capillaritis, and phlebitis.
- Mixed forms: unclassifiable vascular lesions of various calibers.
Depending on the depth of wall involvement, there is endovasculitis (inner layer), mesovasculitis (middle layer), perivasculitis (outer layer), and panvasculitis, affecting all layers of the vessel.
Mechanisms of development
The pathogenesis is based on damage to the endothelium, which acts as a target for antibodies and lymphocytes. The process goes through three classical phases of inflammation:
- Alteration: disruption of barrier functions, penetration of immune complexes and fibrin into the wall.
- Exudation: edema, plasmorrhagia, and leukocyte infiltration.
- Proliferation: proliferation of adventitial and endothelial cells, which can lead to obliteration of the vascular lumen.
In destructive forms, fibrinoid necrosis is the key link.
Immunopathology
The development of vasculitis is associated with hypersensitivity reactions:
- Immediate-type hypersensitivity (ITH): manifests as destructive changes, fibrinoid necrosis, and pronounced exudation.
- Delayed-type hypersensitivity (DTH): characterized predominantly by productive forms of inflammation, including granulomatous processes.
Briefly: answers to topical questions
Which specific nosological forms belong to primary systemic vasculitides?
Primary systemic vasculitides include the following independent nosological forms and variants of vasculitis:
- Arteritis.
- Allergic granulomatosis (Churg-Strauss syndrome).
- Systemic necrotizing vasculitis.
- Wegener's granulomatosis.
- Mucocutaneous lymph node syndrome (Kawasaki disease).
- Thromboangiitis obliterans (Buerger's disease).
- Polyarteritis nodosa.
- Microscopic polyangiitis.
Which cells form the inflammatory infiltrate in granulomatous vasculitides?
Sources for the granulomatous reaction in Wegener's granulomatosis indicate:
- Lymphoid cells.
- Monocytes.
- Macrophages.
- Fibroblasts.
- Neutrophilic leukocytes — their presence is noted as a specific sign.
Necrotic granulomas may also contain lymphocytes, plasma cells, multinucleated giant histiocytes, and eosinophils; histiocytes can form palisading structures around the necrosis.
What are the possible outcomes and complications in the vascular wall after vasculitis?
Possible outcomes and complications in the vascular wall after vasculitis:
- Sclerosis and thickening of the wall.
- Obliteration (occlusion) of the vascular lumen; microcirculatory vessels may turn into cellular cords without a lumen.
- Thrombosis, resulting from endothelial damage and the release of coagulation factors.
- Aneurysm when vascular wall strength decreases.
- Vessel rupture and hemorrhage, including from an aneurysm or inflammatory vascular wall lesion.
In which infectious diseases is the development of secondary vasculitis typical?
The development of secondary vasculitis is typical for a number of acute and chronic infectious diseases. These include:
- Syphilis — vasculitis is characteristic of the secondary period (rash formation) and tertiary period (involvement of vasa vasorum in mesaortitis).
- Rickettsioses (e.g., epidemic typhus) — cause necrotizing vasculitis with hemorrhages and exanthema.
- Tuberculosis — accompanied by vascular involvement in specific inflammation.
- Scarlet fever — infectious-allergic lesion of the vascular bed.
- Sepsis and subacute bacterial endocarditis — present with alterative-exudative or chronic productive vasculitis.
Remember the levels of involvement using "EMP-P": Endo-, Meso-, Peri-, Panvasculitis (from the inner layer to the complete involvement of all layers).
Class and exam questions
What is the difference between primary and secondary vasculitides?
Primary vasculitides are independent nosological entities. Secondary ones arise as a consequence of vascular involvement in inflammation during other diseases.
What is thromboendovasculitis?
This is an inflammatory destruction of the inner lining of a vessel, accompanied by secondary thrombosis.
Which types of inflammatory reaction predominate in vasculitides?
Necrotic (destructive), destructive-productive, and productive (including granulomatous) forms are distinguished.
What else to study on this topic
- Clinical and morphological features of Wegener's granulomatosis.
- Differential diagnosis of Buerger's disease.
- The role of cytokines and free radicals in vascular wall destruction.
- Transformation of immediate-type hypersensitivity reactions into delayed-type hypersensitivity during the chronic course of vasculitis.
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