Large melanocytic nevi in hereditary epidermolysis bullosa.
Large melanocytic nevi occurring in areas of former blistering in patients with hereditary epidermolysis bullosa (EB) pose a problem to the clinician with regard to prognosis and therapy because they may show clinical and histopathologic features strikingly resembling malignant melanoma. To investigate clinical and histologic criteria as well as the biologic behavior of these nevi, pigmented lesions of 12 patients (EB simplex, n = 1; junctional EB, n = 7; dystrophic EB, n = 4) of the Austrian EB registry were analyzed. Clinically, the nevi are up to palm sized, are initially very dark, and may exhibit stippled pigmentation and irregular borders that outline areas of former blisters. Over time they usually lose pigment, the surface gets papillomatous, and finally they acquire a shagreen-like appearance. Histopathologically, the nevi frequently exhibit a compound congenital or persisting nevus/pseudomelanoma pattern. Despite this combination of features, no malignant transformation of the nevi has been seen by us even after 20 years of prospective surveillance. Because nevi with these criteria do not fit in any of the known categories, we suggest the term EB nevi.