Discohesive malignant melanoma simulating a bullous dermatoses.

A variety of clinical and histological presentations can accompany the evolution of malignant melanoma. Unusual cytological variants of malignant melanoma include balloon cell, signet ring cell, myxoid and other metaplastic changes. With the exception of a case of pemphigus-like changes associated with malignant melanoma in paraneoplastic pemphigus, acantholysis is not a common histopathological feature of malignant melanoma. We present two unique cases of malignant melanoma with varying degrees of extensive melanocytic discohesion in an acantholytic pattern mimicking pemphigus vulgaris, further referred to in this article as 'discohesive melanoma'. Routine direct immunofluorescence studies for pemphigus-related antibodies (IgG and C3) were negative. In one case, indirect immunofluorescence for desmoglein autoantibodies characteristic of pemphigus were negative, although positive antibodies to desmoglein 1 was detected using immunosorbent assay. The differential diagnoses and pitfalls in recognition of this unusual presentation of malignant melanoma along with possible pathogenetic mechanisms are discussed.