‘Could it be mycosis fungoides?’: an approach to diagnosing patch stage mycosis fungoides

Abstract

Mycosis fungoides (MF) is the most common primary cutaneous T cell lymphoma, which is characterised in its early stages by epidermotropism of small to medium-sized T lymphocytes with cerebriform nuclei. Originally described by Alibert in 1806, MF is classically a disease of adults, although children and adolescents can be affected, and it typically has a protracted, indolent course. Routine dermatopathology practice involves many biopsies submitted with a clinical query regarding the possibility of MF. These are not always straightforward, as the histological features can be variable and are not always readily distinguishable from several other clinical differential diagnoses. Whilst modern molecular testing modalities can assist, even these do not always enable a definitive diagnosis of MF in its early stages. We have reviewed the histopathological features of early MF and currently recognised subtypes and the role of immunohistochemistry and emerging molecular techniques in the diagnosis of this condition. We also outline our approach to a biopsy where the question of ‘Could it be MF?’ has been proposed.