[Mycosis fungoides or inflammatory dermatitis: differential diagnosis between early lymphoma and inflammation in skin biopsies].

Mycosis fungoides is a cutaneous T-cell lymphoma with protracted clinical course and progression in different stages with increasing aggressiveness. The clinical picture as well as the histopathology of mycosis fungoides within the early patch and plaque phase is difficult to delineate from some inflammatory skin diseases. Thus, the diagnosis of these early stages of the lymphoma is only possible when clinical, histopathological, and molecular features are integrated into the diagnosis, especially as none of the individual disease criteria is specific. Important clues towards the diagnosis of mycosis fungoides are cytologically abnormal epidermotropic CD4-positive T-cells causing only minor epidermal alterations, the formation of Pautrier-abscesses and basal alignment of the epidermotropic T-cells. The findings of an aberrant T-cell immunophenotype of the intraepidermal lymphoid component as well as the molecular proof of T-cell clonality are important further features. In the differential diagnosis between early stage mycosis fungoides and parapsoriasis, there remains nevertheless a diagnostic and maybe also a true biological grey zone.