An immunohistochemical analysis of pseudomelanocytic nests mimicking melanoma in situ: report of 2 cases

Am J Dermatopathol. 2010 Aug;32(6):633-7. doi: 10.1097/DAD.0b013e3181d1537b.

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.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Biomarkers, Tumor / metabolism
  • Diagnosis, Differential
  • Diagnostic Errors / prevention & control
  • Drug Eruptions / diagnosis*
  • Drug Eruptions / metabolism
  • Female
  • Humans
  • Hyperpigmentation / metabolism
  • Hyperpigmentation / pathology
  • Immunohistochemistry
  • Lichenoid Eruptions / diagnosis*
  • Lichenoid Eruptions / metabolism
  • Melanocytes / metabolism
  • Melanocytes / pathology*
  • Melanoma / diagnosis*
  • Melanoma / metabolism
  • Microphthalmia-Associated Transcription Factor / metabolism
  • Skin Neoplasms / diagnosis*
  • Skin Neoplasms / metabolism

Substances

  • Biomarkers, Tumor
  • MITF protein, human
  • Microphthalmia-Associated Transcription Factor