Metabolic changes at the margin of the spreading psoriatic lesion.

Keratotome slices were cut across the margins of rapidly-spreading psoriatic plaques. Each slice was divided into eight sections and in each section we measured the percentage cells in S phase and the levels of glucose-6-phosphate dehydrogenase (both related to epidermal proliferation), acid phosphatase (associated with keratinization) and alkaline phosphatase (a marker for dermal capillaries). Disturbances in the epidermis extended only 2 to 4 mm into the 'uninvolved' skin, whereas the capillaries were metabolically abnormal for a distance of about 2 cm ahead of the advancing edge of the plaque. This implies that changes in the capillary may precede those in the epidermis during the spread of the psoriatic lesion.