Many clinically characteristic psoriatic plaques present histological evidence of relatively low mitotic activity. The mitotic index in individual lesions is related to the amount of parakeratosis at the base of the stratum corneum. Alternating layers of corneal orthokeratosis and parakeratosis, frequent in psoriasis, suggest that epidermal growth activity fluctuates in the lesions even without treatment. This indicates that a control mechanism operates to a variable degree in psoriatic lesions. It is suggested that this represents a mechanism which, when better understood, might be utilized in treatment or prevention of the disease.
Cox AJ, Watson W. Histological Variations in Lesions of Psoriasis. Arch Dermatol. 1972;106(4):503-506. doi:10.1001/archderm.1972.01620130035008