Exactly how vascular damage develops in vasculitis isn’t well understood. Some think that vasculitis may follow serious infectious disease, such as hepatitis B and bacterial endocarditis, and may be related to high doses of antibiotics.

Current theory holds that vasculitis is initiated by excessive circulating antigen, which triggers the formation of soluble antigen-antibody complexes. Then, because the reticuloendothelial system can’t effectively clear these complexes, they’re deposited in blood vessel walls (type 3 hypersensitivity). Theorists think that increased vascular permeability (associated with release of vasoactive amines by platelets and basophils) enhances this deposition. The deposited complexes activate the complement cascade. The result: chemotaxis of neutrophils, which release lysosomal enzymes, which, in turn, cause vessel damage and necrosis. These effects may precipitate thrombosis, occlusion, hemorrhage, and tissue ischemia.

An additional factor in certain types of vasculitis is the formation of auto antibodies directed at the body’s own cellular and extracellular proteins, which can lead to the activation of inflammatory cells or cytotoxicity (a type 2 hypersensitivity reaction). Patented antibodies being studied include those directed against cytoplasmic antigens of neutrophils and monocytes (antineutrocytoplasmic antibodies known as cANCA or pANCA) and those directed against surface antigens of endothelial cells (antiendothelial cell antigens or AECA). The exact role of acute antibodies remains unclear.

Another mechanism that may contribute to vascular damage is the cell-mediated (T-cell) immune response, whereby circulating antigen triggers sensitized lymphocytes to release soluble mediators. This attracts macrophages, which release intracellular enzymes, causing vascular damage. They can also transform into the epithelioid and multinucleated giant cells that typify the granulomatous vasculitides. Macrophagic phagocytosis of immune complexes enhances granuloma formation.

Atopic individuals can develop vasculitis after exposure to allergens. This type 1 hypersensitivity can lead to mast cell degranulation, hyperesinophilia, and inflammation, which, in turn, can lead to vasculitis.

Renal, cardiac, and hepatic involvement can be fatal if vasculitis isn’t treated. Renal failure, renal hypertension, glomerulitis, fibrous scarring of the lung tissue, cerebrovascular accident, and GI bleeding are a few of the severe complications associated with vasculitis. Others include necrotizing vaculitis, spontaneous hemorrhage, intestinal obstruction, myocardial infarction, pericarditis, and rupture of mesenteric aneurysms.

The patient’s history and the physical assessment findings will vary, depending on the blood vessels involved. (See Types of vasculitis, pages 956 to 959.)

Not all vasculitis disorders can be diagnosed definitively by specific tests. The most useful general diagnostic procedure is biopsy of the affected vessel. In some
disorders, arteriography may be informative.

Appropriate treatment aims to minimize irreversible tissue damage associated with ischemia. In primary vasculitis, treatment may involve removal of an offending antigen or use of anti-inflammatory or immunosuppressant drugs. Antigenic drugs, food, and other offending environmental substances should be identified and eliminated, if possible.

Drug therapy in primary vasculitis typically involves daily administration of low-dose oral cyclophosphamide and corticosteroids. Antihypertensives for acute pain are also given.