Corneocyte morphology and formation rate in lichen planus and experimental parakeratosis in subjects with and without psoriasis.

In a recent paper changes in corneocyte morphology and formation rate in psoriasis have been established. In the present study the specificity of these alternations were analysed in two situations. Early lichen planus papules were chosen as a model of hyperproliferation with hypergranulosis and orthohyperkeratosis. Hyperproliferation with parakeratosis was induced by nonanoic acid (CH3(CH2)7COOH) as an experimental model in psoriatics and non-psoriatics. In lichen planus papules, the rate of corneocyte layer formation was 2.4 times that of the non-involved skin. In psoriasis, a similar rate was found in parts with hypergranulosis. A 13% decrease in corneocyte diameter took place in lichen planus lesions--similar to that found in psoriasis. The corneocytes in lichen planus were also thicker than normal cells, though their volumes were similar. Thickness decreased in more superficial locations of these corneocytes. Swelling was a finding during the histological procedure, Corneocytes in the lesion increased markedly in volume, due to swelling. The parakeratosis elicited by nonanoic acid showed cells with irregular membranes and nuclei with non-flattened and irregular borders. The rate of corneocyte layer formation was 2.6 times that of the normal skin. The epidermal reaction to the superficial damage by nonanoic acid did not differ between psoriatics and non-psoriatics. This type of parakeratosis was distinctly different from that present in psoriasis.