Reassessment of histologic parameters in the diagnosis of mycosis fungoides.

The histologic diagnosis of mycosis fungoides (MF) can be difficult to establish and is based on interpretation of numerous subtle changes, most of which may be present to some degree in many inflammatory and neoplastic cutaneous conditions. To reassess the diagnostic criteria for making a histologic diagnosis of MF, we retrospectively reviewed histologic sections from 64 patients with mycosis fungoides (MF+) and compared the findings with sections from 47 patients who were biopsied to exclude MF and were shown not to have the disease (MF-). Patients were selected as MF+ or MF- independent of histologic findings based on the clinical course with at least 3 years of follow-up and immunophenotyping results. Following patient selection, at least two observers reviewed each slide without knowledge of final diagnosis and graded the intensity of approximately 25 histologic parameters. On univariate analysis, the following parameters were significant at beyond the p = 0.01 level: Pautrier's abscesses, haloed lymphocytes, exocytosis, disproportionate epidermotropism, epidermal lymphocytes larger than dermal lymphocytes, hyperconvoluted intraepidermal lymphocytes, and lymphocytes aligned within the basal layer. Haloed lymphocytes proved to be the most robust discriminator of MF from non-MF on multivariate analysis. These findings show that whereas many previously described features do discriminate between MF and inflammatory mimics, others are much less specific. Furthermore, few cases demonstrate all histologic features; for example, Pautrier's microabscesses were seen in only 37.5% of our cases. We conclude that a combination of specific histologic parameters can be used to establish a microscopic diagnosis of MF without the necessity of confirmatory immunophenotyping in the vast majority of cases.