Strict anatomical coexistence of vitiligo and psoriasis vulgaris--a Koebner phenomenon?

We describe a patient who developed typical psoriatic plaques covering completely or partly the vitiliginous areas of her skin. Her psoriasis was strictly limited to the vitiliginous patches with no involvement of the normal skin. Strict anatomical coexistence of both diseases is extremely rare and suggests a causal mechanism, possibly due to a Koebner phenomenon, but genetic and environmental factors may also be involved.