Powell FC, et al.: Pyoderma gangrenosum: classification and management. J Am Acad Dermatol 34: 395-409, 1996
van der Sluis I: Two cases of pyoderma (ecthyma) gengraenosum associated with the presence of an abnormal serumprotein (beta-2-A-paraprotein). With a review of the literature. Dermatologica 132: 409-424, 1966