Histopathologic approach to epidermotropic lymphocytic infiltrates

Mycosis fungoides is the most common and therefore quintessential cutaneous lymphoma and is typically characterized by an epidermotropic infiltrate of atypical monoclonal CD4+ lymphocytes. Classical histopathologic findings include epidermotropism, lymphocytes with convoluted nuclear contours and surrounding perinuclear "halos," and papillary dermal fibrosis. Atypical lymphocytes may occasionally form Pautrier's microabscesses with tagging of lymphocytes along the basal keratinocytes. Unfortunately, a variety of benign inflammatory infiltrates, as well as other cutaneous lymphomas, may demonstrate some similar histopathologic findings. Herein, we review the wide array of epidermotropic T-cell lymphomas and discuss distinguishing features between these entities. We also offer an algorithmic approach utilizing histopathologic, immunophenotypic, and molecular techniques that can be used for analyzing an epidermotropic T-cell infiltrate in order to render a specific diagnosis.