Pathology of the Cutaneous Vasculitides: A Comprehensive Review

Vasculitis has historically been poorly defined and the histological and clinical manifestations are protean, further complicating the diagnostic process. The definitive diagnosis is made by evidence of histologic effacement of a vessel with associated transumural inflammatory infiltrate of that vessel. Vasculitis can be a primary process or secondary to disseminated intravascular coagulation, ulceration, arthropod assault, and/or suppurative infiltrates (for example pyoderma gangrenosum). Vasculitis must further be distinguished from vasculopathies, particularly livedoid vasculopathy and connective tissue diseases (namely scleroderma and systemic lupus erythematosus) in which the primary process is vascular fibrin thrombi of the upper dermal vessels. A necrotizing vasculitis resulting secondary to the thrombotic process can occur, blurring the lines between true vasculitis and vasculopathy. Very few vasculitic processes have pathognomonic histological findings. Often times the dermatopathologist and clinician must work in concert and combine clinical, histological, and laboratory data to determine what the primary process is. As previously stated, histological evidence of inflammatory infiltrate within the vessel wall must be seen in order to diagnose vasculitis. Associated findings include fibrinoid necrosis, endothelial swelling, and endothelial cell apoptosis (Carlson, et al., 2005). Other secondary changes including extravasation of red blood cells, necrosis, ulceration, and neovascularization suggest that there has been vascular damage (Carlson et al., 2005). Associated changes can also be seen in the sweat glands and include basal cell degeneration, necrosis, and basal cell hyperplasia (Akosa & Lampert, 1991). Changes in the adjacent tissue can aid the dermatopathologist in determining what the underlying etiology causing the vasculitis could be. Extravascular granulomas characterized by degenerating collagen bundles surrounded by eosinophils and flame figures (“red” granulomas) are seen in Churg Strauss Syndrome while extravascular granulomas characterized by degenerating collagen bundles surrounded by basophilic debris (“blue” granulomas) are seen in Wegener’s granulomatosis and rheumatoid vasculitis (Carlson, 2010). Dermal lamellar fibrosis can be seen in erythema elevatum diutinum and granulomas faciale (Carlson et al., 2005). Direct immunofluorescence adds another important diagnostic piece of information. Absence of immune complex deposition (pauci-immune vasculitis) is seen in Wegener’s granulomatosis, microscopic polyangiitis, and Churg Strauss syndrome (Carlson, 2010).