Interface change in early mycosis fungoides: A potential mimicker of benign dermatoses

Background: Histopathologic features of interface dermatitis can occasionally be seen in mycosis fungoides (MF), particularly in early patch-stage disease. Materials and Methods: We identified six patients with MF whose early biopsy specimens showed such prominent interface dermatitis that a benign diagnosis was favored. All subsequent specimens were reviewed for these patients, and the histopathologic evolution of disease was documented. Immunohistochemistry (IHC) for CD2, CD3, CD4, CD5, CD7, CD8, CD30, and CD123 was performed retrospectively. Educational archives were reviewed to assess the incidence of interface dermatitis in biopsies otherwise diagnostic of MF. Results: A spectrum of vacuolar and lichenoid patterns of interface change was observed in this series of six patients eventually diagnosed as having MF, and was seen as a recurring pattern in multiple specimens over time. In retrospect, findings described in early MF such as lining up of lymphocytes along the dermal-epidermal junction within the basal layer, papillary dermal fibrosis, and intraepidermal lymphocyte atypia could be appreciated to varying degrees in the confounding specimens. CD123 was negative in all cases, putatively excluding a connective tissue disease (CTD). None of the early biopsies showed loss of pan-T antigens CD2, CD5, and CD7. Forty-six of 164 cases (28%) of MF in an archival study set showed varying degrees of interface dermatitis in the setting of otherwise diagnostic changes of MF. Conclusions: Early MF can show prominent interface change and mimic inflammatory dermatoses. Histopathologic clues suggestive of MF should be carefully assessed, and IHC for CD123 may be helpful in distinguishing MF from CTD. Repeat biopsies over time may be necessary to arrive at a definitive diagnosis, in conjunction with ancillary studies and strong clinicopathologic correlation.