Psoriasis was associated with vitiligo in two cases. In both cases, psoriatic lesions appeared sharply demarcated in vitiliginous skin. The phenomenon is regarded as a significant biologic response and more than a chance coincidence of the two diseases in the same location.
De Moragas JM, Winkelmann RK. Psoriasis and Vitiligo. Arch Dermatol. 1970;101(2):235-237. doi:10.1001/archderm.1970.04000020105017