Early mycosis fungoides vs. inflammatory mimics: How reliable is histology?

Background: The histologic diagnosis of early mycosis fungoides (MF) and its distinction from inflammatory dermatoses is challenging, owing to the overlap of several features. Aims: 1) To assess the efficacy of histologic criteria to diagnose early MF, 2) to study their utility in differentiating inflammatory mimics of MF. Methods: We retrospectively reviewed slides from 50 cases clinically/histologically suspicious for MF. The diagnoses were established based on response to treatment and follow-up. The slides were analyzed double-blinded by two observers independently. Twenty-eight histologic criteria were assessed and each criterion was graded. Univariate analysis was performed on the results. Results: There were 17 cases of MF and 33 of inflammatory dermatoses. Of the 28 criteria, the following 15 achieved significance on univariate analysis: disproportionate epidermotropism, tagging of lymphocytes along the basal layer, haloed lymphocytes, convoluted lymphocytes, Pautrier's abscesses, larger epidermal lymphocytes, wiry dermal collagen, absence of edema, eccrine infiltration, folliculotropism, follicular mucin, involvement of papillary and reticular dermis, monomorphous infiltrates, and atypia of dermal lymphocytes. The criteria that were 100% specific for MF included convoluted lymphocytes, eccrine infiltration, and follicular mucin. Absence of edema was 100% sensitive and specific in distinguishing MF from its inflammatory mimics. Conclusions: A combination of histologic patterns and cytology of lymphocytes is reliable in distinguishing MF from inflammatory dermatoses. No single criterion is effective in achieving this. Rather than merely recording the presence or absence of a criterion, grading each of them adds objectivity to the diagnosis.