Systemic administration of methotrexate produced histologically damaged cells in biopsy specimens of skin taken from areas clinically consistent with psoriasis. These cells were not found in the epidermis of uninvolved, normal appearing skin biopsy specimens taken from the same patient at the same time intervals. In addition, the appearance of the damaged cells was related to the dosage of methotrexate administered.
Similarly damaged cells were seen after administration of hydroxyurea. Again, selective cytotoxicity was noted in that damaged appearing cells were present in involved psoriatic epidermis and were absent in uninvolved normal appearing epidermis.
No damaged cells were seen in biopsy specimens obtained from untreated psoriatic patients or patients treated with steroids administered topically or systemically.
Smith C, Gelfant S. Effects of Methotrexate and Hydroxyurea on Psoriatic EpidermisPreferential Cytotoxic Effects on Psoriatic Epidermis. Arch Dermatol. 1974;110(1):70-72. doi:10.1001/archderm.1974.01630070038006