The rate of corneocyte formation in microscopic lesions in patients with active psoriasis

Microscopic lesions in active psoriasis were identified after careful examination with a magnifying glass in areas free of macroscopic lesions and of hair follicles. Biopsies were excised without anesthesia, immediately frozen and cryostat-sectioned. Care was taken to preserve the horny layer which was stained to reveal corneocyte membranes and nuclei when present. The interlocking sheets of corneocyte layers made it feasible to outline and trace intercellular spaces parallel to the surface and count the number of corneocyte layers between pairs of these. It was assumed that the location of such a space in the horny layer indicates the period of time from its formation. This information was used to assess the rate of corneocyte layer formation at specified intervals of time. The result shows that adjacent areas of the horny layer could be compared and relative rates of corneocyte layer formation computed. In the parakeratotic part of the early lesions of psoriasis studied the rate of corneocyte layer formation was 15 times higher than that in the non-involved skin. The peak rate, coincident with parakeratosis, was preceded by a number of thickened corneocyte layers. These also showed an increased rate of formation, up to 6.6 times that in non-involved skin. There was no acanthosis in the lesions studied. A subepidermal cellular infiltrate was observed. Periods of rapid corneocyte formation with parakeratosis were often short (not more than one day). These were interrupted by periods with a lower rate. The relationship between corneocyte morphology and stratum corneum kinetics is a distinct feature in the early psoriatic lesion.