Vasculitis most commonly affects the pinnal margins of dogs and cats. Clinical signs can include alopecia, scaling, erosion, ulceration, crusting, and necrosis (Figure 1). In some cases, tissue loss may cause changes to the shape of the pinnae. Vasculitis is a histopathologic reaction pattern that signals the presence of inflammatory cells in blood vessels and is an immunologic response (ie, type III hypersensitivity disorder) that results in damage to vascular components of the dermis or subcutaneous tissue. Clinical signs can result when adequate oxygenation of tissue does not occur and blood vessels are damaged. A diagnosis of vasculitis is typically obtained through biopsy, and the underlying trigger should be determined. Numerous inciting agents have been implicated as factors that cause vasculitis, including drugs, vaccines (most commonly, rabies vaccine), food hypersensitivity, insect bites, malignancies, and infectious organisms. Many cases of vasculitis are idiopathic.1-3
Treatment of vasculitis depends on the severity of the case and the underlying cause. If an inciting cause can be determined, it should be removed and avoided in the future. Any underlying infectious disease that acts as an inciting cause should be treated (eg, tick-borne diseases can be treated with doxycycline). Immunomodulatory medications can be used to treat vasculitis. Pentoxifylline is often the treatment of choice. Pentoxifylline increases erythrocyte flexibility and decreases blood viscosity, thereby allowing increased oxygenation of damaged tissue. For patients that are nonresponsive to pentoxifylline, strong immunosuppressive medications (eg, glucocorticoids, cyclosporine, azathioprine) may be required. Some severe subforms of vasculitis, namely thrombovascular necrosis of the pinnae (Figure 2), may not respond to medication and may require surgical intervention. A partial pinnectomy can be performed, ideally with a CO2 laser, with care taken to remove all affected tissue.2