Histology-based classifier to distinguish early mycosis fungoides from atopic dermatitis.

BACKGROUND: Histopathological differentiation of early mycosis fungoides (MF) from benign chronic inflammatory dermatoses remains difficult and often impossible, despite the inclusion of all available diagnostic parameters. OBJECTIVE: To identify the most impactful histological criteria for a predictive diagnostic model to discriminate MF from atopic dermatitis (AD). METHODS: In this multicentre study, two cohorts of patients with either unequivocal AD or MF were evaluated by two independent dermatopathologists. Based on 32 histological attributes, a hypothesis-free prediction model was developed and validated on an independent patient's cohort. RESULTS: A reduced set of two histological features (presence of atypical lymphocytes in either epidermis or dermis) was trained. In an independent validation cohort, this model showed high predictive power (95% sensitivity and 100% specificity) to differentiate MF from AD and robustness against inter-individual investigator differences. LIMITATIONS: The study investigated a limited number of cases and the classifier is based on subjectively evaluated histological criteria. CONCLUSION: Aiming at distinguishing early MF from AD, the proposed binary classifier performed well in an independent cohort and across observers. Combining this histological classifier with immunohistochemical and/or molecular techniques (such as clonality analysis or molecular classifiers) could further promote differentiation of early MF and AD.

Histopathological Spectrum and Immunophenotypic Characterization of Symmetrical Drug-Related Intertriginous and Flexural Exanthema.

INTRODUCTION: Symmetrical drug-related intertriginous and flexural exanthema (SDRIFE) is a clinically very well-defined drug eruption, but the histopathological findings are still considered to be nonspecific. OBJECTIVES: To characterize the histopathological and immunophenotypical features of SDRIFE. MATERIAL AND METHODS: We performed a retrospective study that identified 11 biopsies from 9 patients with SDRIFE. The histopathological features were analyzed in conjunction with the immunohistochemical findings. RESULTS: The most common histopathological feature was basal cell vacuolization, which was often associated with necrotic keratinocytes and focal spongiosis. TIA1+ T cells and neutrophils were frequently detected in the epidermis and at the dermoepidermal junction. The dermal inflammatory infiltrate was mixed, consisting of CD3+ T cells, macrophages, granulocytes, low numbers of CD20+ B cells, and plasma cells. A combination of histopathological patterns was observed in 5 cases. The most frequent combined histopathological patterns were interface dermatitis, spongiotic dermatitis, and psoriasiform dermatitis. Other histopathological patterns found in different combinations were pustular dermatitis, perivascular and interstitial neutrophilic dermatitis, and interstitial granulomatous dermatitis. In the other 4 cases, a single histopathological pattern predominated, such as psoriasiform dermatitis, vacuolar interface dermatitis of erythema multiforme-like type, or superficial and deep perivascular and interstitial dermatitis with eosinophils and neutrophils. CONCLUSIONS: SDRIFE is characterized histologically by a vacuolar interface dermatitis induced by cytotoxic T lymphocytes and neutrophilic granulocytes. This pattern may be obscured by accompanying spongiotic, psoriasiform, or pustular features combined with a mixed superficial and sometimes deep dermal infiltrate.