Localized areas of psoriasis in nine patients have been treated with topical methotrexate. Clinically, the lesion improved in all instances and in three there was complete clearing. All the patients except one had a reaction in the skin surrounding the treated lesions. This took the form of erythema, and purpura, and in three instances ulceration. Only two patients showed any similar reactions in the psoriatic lesion.
Histologically, there was improvement in the psoriasis in six of the patients within 48 hours. The first sign was the reformation of a granular layer, which in three specimens was normal after one week's treatment.
The action of topical methotrexate in psoriasis appears to be directly on the epidermal cells.
Fry L, McMinn RMH. Topical Methotrexate in Psoriasis. Arch Dermatol. 1967;96(5):483-488. doi:10.1001/archderm.1967.01610050005001