Methotrexate administration to patients with psoriasis results in clinical improvement over a period of weeks unaccompanied by any observable change in the uninvolved skin. Biochemically, enzyme activities are decreased in both the involved and noninvolved skin. The decreases in the involved areas correlate fairly well with the observed clinical improvement. The specific relative pattern of the increased enzyme activities characteristic of the psoriatic lesion is lost when enzyme activities are depressed by the action of methotrexate.
Halprin KM, Ohkawara A. MethotrexateEffects on the Enzymes of Carbohydrate Metabolism in Psoriasis. Arch Dermatol. 1967;96(5):565-571. doi:10.1001/archderm.1967.01610050087015