Leukocytoclastic Vasculitis and Microvascular Occlusion: Key Concepts for the Working Pathologist.

Although clinicians often put vasculitis and microvascular occlusion in the same differential diagnosis, biopsy findings often are either vasculitis or occlusion. However, both vasculitis and occlusion are present in some cases of levamisole-associated vasculopathy and certain infections. Depth of dermal involvement and vessel size should be reported, because superficial and deep small vessel leukocytoclastic vasculitis and/or involvement of medium-sized vessels may be associated with systemic disease. Microvascular occlusion of vessels in the fat should prompt consideration of calciphylaxis. Clues to ultimate clinical diagnosis can be garnered from depth of involvement, size of vessels affected, and presence of both vasculitis and occlusion.