Light and electron microscopy of excoriated psoriatic lesions in patients during topical treatment.

This is a light- and electron-microscopic study of excoriated, recalcitrant psoriatic lesions in ambulatory patients undergoing topical treatment. During regeneration of a stratum corneum without scales, in areas showing excoriations bounded by a non-cornified epidermis, horny cell layers, designated I and II, are formed. In areas in which excoriations are delimited by an epidermis with a retained stratum corneum, the latter is composed of a horny cell layer I and/or II or III. The horny cell layers differ, as shown by light- and electron-microscopy. In the less fresh excoriations, a homogeneous substance, which includes fibrin deposits, is observed. This substance is also seen frequently in the stratum corneum. In the less fresh excoriations and in the stratum corneum there are numerous polymorphonuclear leukocytes. In these locations, however, they are only found simultaneously with the homogeneous substance containing fibrin deposits. Polymorphonuclear leukocytes are also seen in the dermal papillae and in the non-cornified epidermis, particularly in the macroscopically "old" excoriations. The changes observed in these recalcitrant lesions have been interpreted as secondary and are believed to be expressions of a non-specific reaction to the mechanical damage to which the ambulatory patients have constantly exposed the lesions. They are not interpreted as changes in the psoriatic condition per se.