Many forms of vasculitis can affect the skin, the most common one being leukocytoclastic vasculitis. Other forms of vasculitis known to affect the skin as well as other organ systems include Churg-Strauss vasculitis, Henoch-Schönlein purpura, Wegener’s granulomatosis, polyarteritis nodosa, and urticarial vasculitis. Leukocytoclastic vasculitis is by far the most commonly encountered of the cutaneous vasculitides. The causes and pathomechanisms vary, and diagnosis and treatment depend on the results of the clinical and histological evaluations.
Clinical Findings: Leukocytoclastic vasculitis most commonly affects the lower extremity or dependent areas of the body. For example, this form of vasculitis is most commonly seen on the legs of ambulatory patients but on the back and buttocks of bedridden patients. The clinical hallmark of vasculitis is the presence of palpable purpura. The rash may start as small, pink, violaceous macules that rapidly develop into red or purple palpable papules; hence the term palpable purpura. Most of the lesions of palpable purpura are uniform in size, but they can range from minute to 1 cm or more in diameter. Patients are most likely to complain of mild itching or no symptoms at all, and the appearance of the rash is what brings them to see the clinician. Mild constitutional symptoms are often present, with mild fever, fatigue, and malaise most commonly reported. Skin-specific symptoms can range from mild pruritus to pain and tenderness to palpation.
The etiology of cutaneous leukocytoclastic vasculitis is heterogeneous. The three most common causes are infections, medications, and idiopathic causes. Almost every possible infection (bacterial, viral, parasitic, and fungal) has been reported to be an initiating factor for leukocytoclastic vasculitis. Medications are a common culprit and can easily be overlooked if a thorough history is not obtained. If the offending infection is treated properly or the offending medication is removed, the vasculitis resolves in approximately 1 month. The symptoms also cease, often faster than the rash resolves. Postinflammatory hyperpigmentation with some hemosiderin deposition often is a residual finding after the lesions have cleared. This resolves slowly over 6 to 12 months.
Pathogenesis: Leukocytoclastic vasculitis is a type III hypersensitivity reaction. Soluble antigens are believed to become complexed with antibodies. As these antigenantibody complexes enlarge, they get trapped in the tiny vasculature of the dependent regions of the body. There, they can initiate the complement cascade and cause endothelial cell wall death, recruitment of neutrophils, and continued blood vessel destruction, leading to the typical cutaneous findings.
Histology: The pathology is centered on the blood venules in the dermis. A prominent neutrophilic infiltrate is present. Degeneration of the neutrophils is always seen, with nuclear dust; this is termed leukocytoclasis. Fibrinoid necrosis of the vessel walls is easily seen. Extravasated red blood cells are seen in the vicinity of the vasculitis. Thrombosis of affected vessel walls is a secondary finding and is not the primary pathology.
Treatment: Therapy is based on the cause of the leukocytoclastic vasculitis. New offending medications should be withdrawn and replaced with substitutes of a different class. Infections need to be thoroughly treated. The use of topical high-potency corticosteroids is helpful in some cases, and oral steroids may be used in medication-induced leukocytoclastic vasculitis. In cases of infection-induced vasculitis, prednisone should be reserved until after the infection has been properly treated. Idiopathic vasculitis is treated with oral steroids, and often a search for an infection or other cause is undertaken. A thorough history and physical examination are needed, as well as some screening laboratory tests. Laboratory testing usually is not helpful unless the history or review of symptoms points in a particular direction. If patients are suffering from more than just very mild systemic symptoms, an evaluation should be done to rule out the more serious forms of vasculitis.