Superimposed linear psoriasis unmasked by therapy with adalimumab.

Several inflammatory skin disorders with a polygenic mode of inheritance (e.g. psoriasis, atopic dermatitis, vitiligo, and lichen planus) sometimes show, by way of exception, a segmental distribution. Superimposed linear psoriasis is an exceedingly rare disorder, but it has been found in both vulgaris and pustular types. This manifestation is probably either due to postzygotic allelic loss at one of the responsible gene loci, or to a postzygotic new mutation at an additional predisposing gene locus. In our case, a unilateral Blaschko-linear distribution was unmasked after treatment of severe non-segmental psoriasis with adalimumab (Humira(R)), reflecting an increased mutational burden of the segmentally involved area.