Dermal and epidermal involvement in the evolution of acute eruptive guttate psoriasis vulgaris.

A light and electron microscopic study of the evolution of acute eruptive guttate psoriasis vulgaris (AEGP) following penicillin-treated streptococcal throat infection is presented. The earliest recognizable changes, distinguished in clinically normal psoriatic skin (CNPS) from patients with psoriasis of 2 days' duration, comprised mast cell degranulation (Type I MCD), a vascular pattern showing endothelial cell gaps in postcapillary venules and postcapillary venules with endothelial cell hypertrophy and compressed lumen as well as epidermal involvement with punctiform spongiotic areas (PSAs). These early dermal and epidermal changes suggest that Type I MCD represents a primary morphologic event. Inflammatory infiltrate of mononuclear cells and exocytosis of mononuclear cells into the PSAs appeared when the concomitant overt psoriasis was 5-21 days old, and these changes were persistent in psoriatic lesions (PLs) of 2 days' duration. They are suggested to be precursors of overt psoriasis. In 2-day-old PLs, MCD (Types I and II) was a prominent feature. It was associated with (1) more extensive vascular changes, (2) inflammatory infiltrate of mononuclear cells and scanty polymorphonuclear leukocytes, (3) epidermal hyperplasia, and (4) migration of a few polymorphonuclear leukocytes through the epidermis with formation of Munro microabscesses in parakeratotic areas of stratum corneum. From the morphologic viewpoint, the progression from 2-day-old to fully evolved PLs seemed basically to be quantitative. The demonstration of MCD as a salient feature in the evolution of AEGP may have future therapeutic and preventive implications for psoriasis.