Vasculitis, inflammation of the vessel wall, can result in mural destruction with hemorrhage, aneurysm formation, and infarction, or intimal-medial hyperplasia and subsequent stenosis leading to tissue ischemia. The skin, in part due to its large vascular bed, exposure to cold temperatures, and frequent presence of stasis, is involved in many distinct as well as un-named vasculitic syndromes that vary from localized and self-limited to generalized and life-threatening with multi-organ disease. To exclude mimics of vasculitis, diagnosis of cutaneous vasculitis requires biopsy confirmation where its acute signs (fibrinoid necrosis), chronic signs (endarteritis obliterans), or past signs (acellular scar of healed arteritis) must be recognized and presence of extravascular findings such as patterned fibrosis or collagenolytic granulomas noted. Although vasculitis can be classified by etiology, many cases have no identifiable cause, and a single etiologic agent can elicit several distinct clinicopathologic expressions of vasculitis. Therefore, the classification of cutaneous vasculitis is best approached morphologically by determining vessel size and principal inflammatory response. These histologic patterns roughly correlate with pathogenic mechanisms that, when coupled with direct immunofluorescent examination, anti-neutrophil cytoplasmic antibody (ANCA) status, and findings from work-up for systemic disease, allow for specific diagnosis, and ultimately, more effective therapy. Herein, we review cutaneous vasculitis focusing on diagnostic criteria, classification, epidemiology, etiology, pathogenesis, and evaluation of the cutaneous vasculitis patient.

Vasculitis is an inflammatory process affecting the vessel wall and leading to its compromise or destruction and subsequent hemorrhagic and ischemic events. Vasculitis can be classified as a primary phenomenon (e.g. idiopathic cutaneous leukocytoclastic angiitis or Wegener granulomatosis) or as a secondary disorder (connective tissue disease [CTD], infection, or adverse drug eruption-associated vasculitis). Cutaneous vasculitis may present as a significant component of many systemic vasculitic syndromes such as rheumatoid vasculitis or anti-neutrophil cytoplasmic antibody (ANCA)-associated primary vasculitic syndromes (Wegener granulomatosis, Churg-Strauss syndrome, microscopic polyangiitis). Cutaneous vasculitis manifests most frequently as palpable purpura or infiltrated erythema indicating dermal superficial, small-vessel vasculitis, and less commonly as nodular erythema, livedo racemosa, deep ulcers, or digital gangrene implicating deep dermal or subcutaneous, muscular-vessel vasculitis. A biopsy extending to the subcutis taken from the most tender, reddish or purpuric lesional skin is the key to obtaining a significant diagnostic result and serial sections are often required for identifying the main vasculitic lesion. Coexistence of pan-dermal small-vessel vasculitis and subcutaneous muscular-vessel vasculitis usually indicates CTD, ANCA-associated vasculitis, Behçet disease, or malignancy-associated vasculitis. A concomitant biopsy for direct immunofluoresence evaluation contributes to accurate diagnosis by distinguishing IgA-associated vasculitis (Henoch-Schönlein purpura) from IgG-/IgM-associated vasculitis, which has prognostic significance. Treatment for cutaneous vasculitis should include avoidance of triggers (excessive standing, infection, drugs) and exclusion of vasculitis-like syndromes (pseudovasculitis) such as thrombotic disorders (e.g. anti-phospholipid antibody syndrome). In most instances, cutaneous vasculitis represents a self-limited condition and will be relieved by leg elevation, avoidance of standing, and therapy with NSAIDs. For mild recurrent or persistent disease, colchicine and dapsone are first-choice agents. Severe cutaneous disease requires treatment with systemic corticosteroids or more potent immunosuppression (azathioprine, methotrexate, cyclophosphamide). A combination of corticosteroids and cyclophosphamide is required therapy for systemic vasculitis, which is associated with a high risk of permanent organ damage or death. In cases of refractory vasculitis, plasmapheresis and intravenous immunoglobulin are viable considerations. The new biologic therapies that act via cytokine blockade or lymphocyte depletion, such as the tumor necrosis factor-alpha inhibitor infliximab and the anti-B-cell antibody rituximab, respectively, are showing benefit in certain settings such as CTD and ANCA-associated vasculitis.

Twenty cases diagnosed as cutaneous polyarteritis nodosa (CPN) and confirmed by skin biopsy over the last 17 years were reviewed in our department. Based upon their clinical features, laboratory findings, and long-term observation of the disease course, they were divided into three groups. 1) Group 1 comprised 16 cases which were classified as the mild cutaneous form. The disease was confined to the skin with occasional involvement of peripheral nerves and skeletal muscles of the affected extremity. They generally followed a benign course. 2) Group 2 comprised 2 cases classified as the severe form. Despite severe clinical manifestations and several abnormal laboratory findings, the disease was limited to the skin, muscles, and peripheral nerves without any visceral involvement over follow-up periods of 11 years and 5 years, respectively. 3) Group 3 comprised 2 cases of the progressive form; in these the disease had begun with a cutaneous lesion and progressed to the systemic form after 19 and 18 year periods of recurrent episodes of cutaneous lesions, respectively. One died of gastrointestinal bleeding. In group 3, serum antinuclear antibodies and rheumatoid factor were positive. The autoimmune mechanism seems to play a role in this group. It is clear from the results of this study that not all patients whose vasculitic lesions are apparently limited to the skin remain in a benign course. Long-term follow-up is essential.

Most biopsies of cutaneous vasculitis will exhibit a small vessel neutrophilic vasculitis [leukocytoclastic vasculitis (LCV)] that is associated with immune complexes on direct immunofluorescence examination or, less commonly, antineutrophilic cytoplasmic antibodies (ANCA) by indirect immunofluorescence testing. Is in uncommon for skin biopsy to reveal solely a neutrophilic arteritis signifying the presence of cutaneous polyarteritis nodosa or, if accompanied by significant lobular panniculitis, nodular vasculitis/erythema induratum. In other cases, cutaneous vascular damage (fibrinoid necrosis, muscular vessel wall disruption, or endarteritis obliterans) will be mediated by a nonneutrophilic inflammatory infiltrate. Eosinophilic vasculitis can be a primary (idiopathic) process that overlaps with hypereosinophilic syndrome, or it can be a secondary vasculitis associated with connective tissue disease or parasite infestation. Authentic cutaneous granulomatous vasculitis (versus vasculitis with extravascular granulomas) can represent a cutaneous manifestation of giant cell arteritis, an eruption secondary to systemic disease such as Crohn's disease or sarcoidosis, or a localized disorder, often a post-herpes zoster (HZ) phenomenon. Lymphocytic vasculitis is a histologic reaction pattern that correlates with broad clinical differential diagnosis, which includes connective tissue disease - mostly systemic lupus erythematosus (SLE), endothelial infection by Rickettsia and viruses, idiopathic lichenoid dermatoses such as perniosis or ulcerative necrotic Mucha-Habermann disease, and angiocentric cutaneous T-cell lymphomas. Skin biopsy extending into the subcutis, identifying the dominant inflammatory cell and caliber of vessels affected, extravascular histologic clues such as presence of lichenoid dermatitis or panniculitis, and correlation with clinical data allows for accurate diagnosis of these uncommon vasculitic entities.

Morphologic changes including formation of vessel wall fibrinoid necrosis in evolution of cutaneous polyarteritis nodosa (C-PAN) have not been described in detail. Therefore, an investigation of 18 skin biopsy specimens from 14 cases of clinicohistologically proven C-PAN was performed. The results indicated that evolution of arteritis can be classified into 4 stages. Coexistence of different stages was common (50%) in the same or different specimens. The initial (acute) stage shows endothelial loss and fibrin thrombi with neutrophil infiltration without obvious internal elastic lamina disruption and medial fibrinoid necrosis. The second (subacute) stage has mixed cell infiltrates showing a unique intimal target-like fibrinoid necrosis with fibrinoid leakage extending through the disrupted sites of the internal elastic lamina to the media. The third (reparative) stage shows intimal fibroblastic proliferation and perivascular neovascularization with predominant infiltrates of histiocytes and lymphocytes. The final (healed) stage has minimal cellular inflammation with occlusive intimal thickening. Overall, our results show that there are 4 stages in the evolution of C-PAN. The initial change occurs in the intima, and the role of internal elastic lamina in preventing intimal fibrinoid necrosis from discharging into the media may account for the development of target-like fibrinoid necrosis in C-PAN.