This polymorphous lymphoma involves the skin only, except in some rare cases that terminally invade the lymph nodes and the visceral organs. As is true with most lymphomas, the histology may change gradually to another form of lymphoma, with progression of the disease. However, most cases of mycosis fungoides begin as such and terminate unchanged.
Mycosis fungoides is a T (thymus-derived) helper cell lymphocyte malignancy. The name cutaneous T-cell lymphoma is preferred by many. Monoclonal antibodies and gene rearrangement studies may help in the histologic diagnosis of this disease.
Associations with human T-cell lymphotrophic virus types I and II and Epstein-Barr virus are found in some patients with mycosis fungoides.
DESCRIPTION. The clinical picture of this disease is classic and is divided into three stages: the erythematous stage, the plaque stage, and the tumor stage. The course usually proceeds in order, but all stages may be evident at the same time, or the first two stages may be bypassed (the d'emblée type of tumor stage mycosis fungoides).
Erythematous stage: Commonly seen are scaly, red, rather sharply defined patches that resemble atopic eczema, psoriasis, or parapsoriasis. The eruption may become diffuse as an exfoliative dermatitis. Itching is usually quite severe.
Plaque stage: The red scaly patches develop induration and some elevation, with central healing that results in ring-shaped lesions. This stage is to be differentiated from tertiary syphilis, psoriasis, erythema multiforme perstans, mycotic infections, and other lymphomas.
Tumor stage: This terminal stage is characterized by nodular and tumor growths of the plaques, often with ulceration and secondary bacterial infection. These tumors are to be differentiated from any of the granulomas (see Chap.20). Prognosis is poor.
COURSE. The early stages may progress slowly, with exacerbations and remissions over many years, or the disease may be rapidly fulminating. Once the tumor stage is reached, the eventual fatal outcome is more imminent. Gene rearrangement studies may help make the diagnosis in skin lesions and may help predict the prognosis of positive lymphadenopathy.
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