Cutaneous lymphocytic vasculitis: a definition, a review, and a proposed classification.

: Lymphocytic vasculitis is not widely accepted as a pathologic mechanism by dermatopathologists, and a comprehensive list of its causes cannot be found in the literature. This state of affairs stems largely from the lack of a rigorous definition. In this report, the authors review past efforts at coming to terms with lymphocytic vasculitis and why those efforts have fallen short. The authors propose that lymphocytic vasculitis can be separated from the ubiquitous perivascular dermatitides in routinely processed specimens by requiring the presence of either acute or chronic damage to the walls of small vessels (eg, fibrin deposition, lamination by pericytes). In the case of muscular vessels, the presence of lymphocytes within the vessel walls is sufficient, because diapedesis of lymphocytes does not occur in arteries or veins. Although lymphocytic infiltrates meeting this definition are uncommon, there are a number of conditions, with both typical and atypical lymphocytes, in which damage to vessels occurs. The authors review these conditions, outline possible pathogenetic mechanisms, ranging from delayed hypersensitivity reactions directed against endothelial cells to direct infection of these cells, and present classifications based on morphological changes and pathogenesis respectively.