Track

Abstract

An 81-year-old man presented with a left supraclavicular 1.5 cm subcutaneous nodule within a longstanding blue-grey 12 cm patch on the left upper chest; smaller patches were on the neck and upper back. Histopathologically, there were sheets of ovoid to spindle cells with amphophilic cytoplasm, open chromatin, and conspicuous nucleoli; the cells stained positively with S100, Mart-1, MiTF and HMB45. FISH detected mutations in RREB1, MYB, and MYC. Biopsy of the larger blue-gray patch revealed pigmented dendritic melanocytes haphazardly dispersed in the upper dermis with occasional balloon cell changes. An initial diagnosis of melanoma arising in a nevus of Ito with balloon cell changes was made. However, primary involvement of the anterior trunk led to reclassification as patch blue nevus. Upon review of the four previously reported cases of melanoma arising within a nevus of Ito, we posit that the latter were better classified as patch blue nevi or plaque blue nevi. We propose that patch blue nevus encompasses a range of lesions, including the primary lesion in this patient, with overlapping features of dermal melanocytoses and melanocytomas. These lesions may be congenital (e.g. congenital segmental dermal melanocytosis) or acquired (e.g. acquired, late-onset, and nevoid dermal melanocytoses; late-onset Ito’s nevus). By definition, a plaque blue nevus is palpable either in its entirety or focally, with histologic features that overlap with common and cellular blue nevi.  We suggest the use of the overarching term patch blue nevus in cases similar to ours to avoid overproliferation of narrowly defined, patient-specific terms.