title: An immunohistochemical analysis of pseudomelanocytic nests mimicking melanoma in situ: report of 2 cases.
abstract: Several case reports have discussed the difficulty in differentiating junctional pseudomelanocytic nests as a result of lichenoid inflammation from a true melanocytic neoplasm. Even immunohistochemistry can be misleading in these cases with both Melan-A and Mart-1 frequently resulting in false positivity as a result of nonspecific labeling of nonmelanocytic cells containing melanosomes. We present a series of 2 similar cases which were initially misdiagnosed as melanoma in situ likely as a result of Mart-1 positivity of the pseudomelanocytic nests. However, in our review, a significant lichenoid reaction was apparent at the dermal-epidermal junction. Staining with microphthalmia-associated transcription factor (MITF) showed a normal density of melanocytes along the dermal-epidermal junction and failed to uniformly label the Mart-1-positive pseudomelanocytic nests. In both patients, medications frequently resulting in fixed drug eruptions were identified, and a final diagnosis of fixed drug eruption was rendered in both cases. In light of these findings we suggest MITF is a more useful marker for evaluating lentiginous proliferations along the dermal-epidermal junction particularly when dealing with the differential diagnosis of lichenoid reaction with pseudomelanocytic nests versus melanoma in situ.
authors.affiliation: Department of Dermatology, Northwestern University Feinberg School of Medicine, Chicago, IL, USA.
authors.forename: Kimberly M
authors.initials: KM
authors.lastname: Nicholson
authors.forename: Pedram
authors.initials: P
authors.lastname: Gerami
mesh_terms: D000328:Adult; D000368:Aged; D014408:Biomarkers, Tumor / Q000378:metabolism; D003937:Diagnosis, Differential; D003951:Diagnostic Errors / Q000517:prevention & control; D003875:Drug Eruptions / Q000175:diagnosis* / Q000378:metabolism; D005260:Female; D006801:Humans; D017495:Hyperpigmentation / Q000378:metabolism / Q000473:pathology; D007150:Immunohistochemistry; D017512:Lichenoid Eruptions / Q000175:diagnosis* / Q000378:metabolism; D008544:Melanocytes / Q000378:metabolism / Q000473:pathology*; D008545:Melanoma / Q000175:diagnosis* / Q000378:metabolism; D051739:Microphthalmia-Associated Transcription Factor / Q000378:metabolism; D012878:Skin Neoplasms / Q000175:diagnosis* / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; C497234:MITF protein, human; D051739:Microphthalmia-Associated Transcription Factor