Investigations of the 'active' edge of plaque psoriasis: vascular proliferation precedes changes in epidermal keratin.

We have investigated markers of epidermal proliferation and differentiation in terms of keratin expression, the morphology of the cutaneous vasculature, and numbers of cutaneous mast cells, in patients with chronic plaque psoriasis. Using the phenomenon of the 'active edge', we have studied these features in the psoriatic plaque itself, and in the clinically normal active and inactive edges of the same plaque. Our results confirm the anticipated changes in keratin profiles, mast cell numbers and psoriatic morphology of the vasculature within the plaque itself. They further indicate that the vascular changes precede the epidermal and mast cell features at the active edge, and that the inactive edge is inactive for all of these variables. Mediators responsible for the vascular proliferation and elongation must be present in increased amounts at the active edge when compared with the inactive, and include locally produced and circulating factors.