Systemic vasculitis

Classification of systemic vasculitides

Since the true cause of vascular inflammation is unknown, the pathologies are divided into groups depending on the size of the blood vessels involved in the pathological process. This is the key criterion that determines the clinical presentation and prognosis.

• Large-vessel involvement: this group includes giant cell temporal arteritis and Takayasu arteritis.
• Medium-vessel involvement: polyarteritis nodosa and Kawasaki disease.
• Small-vessel involvement: the largest group, including granulomatosis with polyangiitis (Wegener's), microscopic polyangiitis, Churg–Strauss syndrome, leukocytoclastic vasculitis, and Henoch–Schönlein purpura.

Kawasaki disease (mucocutaneous lymph node syndrome)

Kawasaki disease is a systemic arteritis that can affect large, medium, and small arteries, though it is primarily associated with a prominent mucocutaneous syndrome. Epidemiologically, the disease is most significant in children aged 2–3 years. In terms of external clinical manifestations, the pathology often resembles measles.

Clinical presentation: The disease has an acute onset. High fever is observed in combination with cervical lymphadenopathy. Mucosal involvement features marked dryness and redness of the lips, forming a characteristic "strawberry tongue". A polymorphic red rash resembling hives appears on the skin. Ocular symptoms include uveitis and photophobia. Musculoskeletal involvement manifests as arthritis and arthralgia.

The most formidable complication is cardiovascular involvement — specifically, involvement of the coronary arteries, which carries a high risk of aneurysm rupture.

Immunopathogenesis of vascular damage:

1. Unknown causative antigens are processed and presented via MHC class I molecules.
2. The cellular response is activated: macrophages become actively engaged, and antigen-specific CD8+ T lymphocytes destroy infected cells.
3. Concurrently, the humoral response is triggered. Antigen-specific IgA B lymphocytes form and differentiate into plasma cells. They secrete antibodies that form pathogenic immune complexes.
4. Macrophages and myofibroblasts release damage mediators: tumor necrosis factor-alpha (TNF-α), vascular endothelial growth factor (VEGF), and matrix metalloproteinases.
5. The end result is destruction of the vascular intima and necrosis of endothelial cells. Cell growth is stimulated on the damaged surface, active thrombosis occurs, and thrombi firmly adhere to the wall.

Hemorrhagic vasculitis (Henoch–Schönlein purpura)

This is a hemorrhagic necrotizing vasculitis that selectively affects small and medium-sized blood vessels. Children aged 2–8 are at risk. A recently tolerated upper respiratory tract infection acts as the triggering factor.

Pathogenesis: The disease has an immune-complex nature. Complexes consisting of antigen, antibody, and complement form in the blood. These structures deposit on vessel walls (small skin capillaries and renal glomeruli are most commonly affected). Neutrophilic infiltrates form at the deposition site, the complement system is activated, and local intravascular coagulation (DIC syndrome) develops. Kidney involvement proceeds via a mechanism similar to IgA nephropathy due to the deposition of IgA and the C3 complement component.

Clinical manifestations:

• Cutaneous syndrome: arises due to increased permeability of the inflamed vessel wall. Hemorrhages develop, manifesting as an abundant, symmetrical papular-hemorrhagic red rash (elements 3 to 10 mm in diameter). The rash is localized predominantly on the extremities and trunk.
• Articular syndrome: pronounced pain in large joints.
• Abdominal syndrome: nausea, vomiting, intense abdominal pain.
• General symptoms: elevated body temperature (fever).

Laboratory diagnostics of systemic inflammation

Laboratory methods are auxiliary in nature, but they are critically important for assessing the severity of the systemic response.

The complete blood count reveals leukocytosis and thrombocytosis (an abnormal increase in the platelet count). An acute-phase reactant shift is characteristic: the erythrocyte sedimentation rate (ESR) and C-reactive protein levels increase significantly (with high values potentially persisting for up to 4–6 weeks). The immune status reflects a generalized increase in immunoglobulin levels.

To confirm the diagnosis of Henoch–Schönlein purpura, serum IgA levels are evaluated (they are elevated), and a tissue biopsy is performed to detect IgA deposits in the skin and renal glomeruli.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Clinical and morphological features of granulomatosis with polyangiitis
• Specifics of large-vessel involvement: Takayasu arteritis and giant cell temporal arteritis
• Differential diagnosis of polyarteritis nodosa
• The role of the complement system in the pathogenesis of local DIC syndrome
• Microscopic polyangiitis and Churg–Strauss syndrome: general characteristics

Other topics in the "Pathology of the Immune System" section

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