Defining lymphocytic vasculitis.

Vasculitis can be defined as vascular inflammation which is usually immune mediated, leading to structural and functional damage to the vessel wall. Our concept of vasculitis has been built around the events surrounding immune-complex-triggered leukocytoclastic vasculitis, while the role of lymphocyte mediated vasculitis remains largely undefined. This may be due to maintaining a stereotypic image of lymphocytic vasculitis as one associated with vascular necrosis, fibrin deposition and haemorrhage and merely substituting lymphocytes for neutrophils. Our understanding of lymphocytic vasculitis may be advanced by identifying the clinical settings in which such reactions may occur, such as autoimmune skin diseases sharing features with graft vs host disease, as well as recognizing that lymphocyte mediated inflammation may lead to a morphologically distinct group of vasculitides, apart from those associated with angiodestruction. Lymphocytic endovasculitis, lymphocytic lichenoid vasculitis and granulomatous vasculitis are potential examples of lymphocytic vasculitis that differ from the histological pattern seen in association with immune complex leukocytoclastic vasculitis. Ultimately, the proof that these vasculitides are examples of lymphocytic vasculitis will rest on new techniques emerging in molecular pathology that have the capacity of analysing the immunological events beyond the current limitations posed by routine histopathology.