Contributor: Gordon K. Klintworth
Mycosis fungoides (granuloma fungoides, epidermotropic T-cell lymphoma) is is the most common cutaneous T-cell lymphoma [lymphoma - cell] and it often presents initially as with flat poorly circumscribed irregular cutaneous macules. The lesions contain erythematous areas and evolve over years to by enlarging and forming plaques and nodules. The erythematous tumors become almost purple in color and frequently ulcerate. Parts of the lesions undergo regression and this accounts for their irregular arcuate, serpiginous and ring shapes. Pruritus may be marked and some hypopigmentation may be present. Mycosis fungoides usually affects elderly individuals and males> females. The lesions have a predilection for non-sun exposed areas, such as the lower abdomen, buttocks and upper thighs. The initial lesions are characterized by a lymphocytic infiltration that is scattered throughout the epidermis with minimal involvement of the dermis. The lower epidermis is mainly involved and Darier-Pautrier microabscesses are present in ~50% of cases. Parakeratosis is common, but spongiosis is not a feature, unless the lesions that have been scratched. Melanocytes may be disrupted in areas of depigmentation. Early lesions may contain more Langerhans cells than normal. Reactive CD8 cells and B-cells may be present, especially in association with spongiosis. The lymphocytes in the lesions are hyperchromatic and slightly enlarged. They have irregular nuclei and their nuclear envelopes have irregular convolutions. Small nucleoli may be evident. Mitotic figures may be present. The neoplastic T-cells express CD4, HLA-DR, but they frequently lack or only partially express other pan T-cell antigens (Leu-8, CD7, CD2, CD3, CD5). In contrast to melanocytes and Langerhans cells in the skin they are S100 protein negative. HTLV-1 is suspected of causing mycosis fungoides.