Cutaneous manifestations of vasculitis in the dog

Abstract

Vasculitis is inflammation of a blood vessel wall. It may be a primary event or develop secondary to inflammation, infection, neoplasia and drugs, particularly vaccinations. Vascular conditions involving the skin are uncommon to rare and present the clinician with a diagnostic and therapeutic challenge. In human medicine considerable debate has been given to establishing a consensus about the definition of systemic vasculitides, particularly primary systemic vasculitis syndromes. The classification of such syndromes is based on the size and location of vessels, and the results of immunohistochemical studies implicate a variety of immune mechanisms including allergic (IgE type 1 hypersensitivity), antibody-mediated including antineutrophil cytoplasmic antibodies, immune complex formation and granulomas. In veterinary medicine there are few primary systemic vasculitides recognised. An example is a multisystemic necrotising vasculitis of small vessels in Beagles called juvenile polyarteritis syndrome (JPS). Cutaneous vasculopathies are usually secondary to an underlying process in which (usually) the small vessels - especially the post-capillary venules - are the target of the disease process. Possible secondary causes of cutaneous vascular disease are listed in Table 1. Histologically there is accumulation of cells (macrophages, neutrophils, lymphocytes and plasma cells) within the vessel wall, injury with necrosis and degeneration of endothelial and smooth muscle cells, and fibrin deposition. Eosinophils may be associated with collagen and necrosis of smooth muscle. Vascular diseases involving skin have been subdivided according to the predominant histological pattern. Vasculitides may be cell poor or granulomatous (macrophage is predominant inflammatory cell). Neutrophilic forms may be leukocytoclastic where neutrophil nuclei undergo pyknosis and karyorrhexis - fragmentation, leading