Mycosis Fungoidessezary Syndrome

General: Mycosis fungoides (MF) is defined as a primary cutaneous T-cell lymphoma that clinically presents with patches and plaques and histologically displays an epidermotropic infiltrate of small- to intermediate-sized cells with atypical, cerebriform nuclei.113 Although some have used the term "cutaneous T-cell lymphoma (CTCL)" synonymously with MF, this practice is to be strongly discouraged because many other types of T-cell lymphoma may also present with primary cutaneous disease. Within the spectrum of MF is a clinical variant condition designated "granulomatous slack skin" characterized by folds of atrophic skin, usually within the axilla or groin. Sezary syndrome is also regarded as a variant of MF and is characterized by peripheral blood involvement by malignant T-cells with cerebriform nuclei, usually associated with adenopathy and erythro-derma.

Pathology: The skin lesions of MF are histologically characterized by an epidermal infiltrate of small- to intermediate-sized cells with irregular, cerebriform nuclei. The presence of such cells in small clusters, known as "Pautrier's microabscesses," is very characteristic of the disease, but in most cases the epidermal infiltrate is present predominantly as scattered, single atypical cells.114 The dermal component may be variable, ranging from a sparse, often band-like, infiltrate in earlier lesions to an extensive collection of malignant cells filling the dermis in advanced stages (Figures 52.19 and 52.20). In a variant form of MF, known as "pagetoid reticulosis," the dermal component is characteristically absent. Some cases of MF are associated with follicular mucinosis, a condition of mucinous changes within a hair follicle accompanied by an infiltrate of malignant cells within the follicular epithelium. The variant known as granulomatous slack skin typically shows a granulomatous infiltrate within the infiltrate, where the admixed lymphocytes include a population of cerebriform cells, similar to those seen in typical MF. In Sezary syndrome, cerebri-form malignant cells are present within the peripheral blood.

Figure 52.19 Mycosis fungoides. At low power, a bandlike lymphocytic infiltrate is seen in the upper dermis

In more advanced disease, there is frequently involvement of lymph nodes, and several schemes have been proposed to grade the extent of nodal involvement. The WHO classification recommends a modification of earlier criteria 113,115,116 to divide cases into three grades of lymph node involvement. In grade I cases, there is no definitive morphologic evidence of nodal involvement. Such cases may show dermato-pathic lymphadenopathy and scattered cerebriform cells, but clusters of atypical cells are not present. In grade II cases, clusters of atypical, cerebriform cells focally efface the lymph node architecture. Lastly, grade III cases demonstrate complete effacement of the nodal architecture by a diffuse infiltrate of malignant cells. Importantly, this scheme is intended to quanti-tate lymph node involvement with a previous diagnosis of MF, and should not be definitively applied to patients without prior, biopsy-proven MF.

Figure 52.20 Mycosis fungoides. At high power, collections of atypical lymphocytes are identified in the epidermis

Immunophenotype: Typically, the malignant cells of MF are positive for T-cell antigens including CD3, CD2, CD5, and, usually, CD4. Occasional cases may lack CD4 and express CD8, especially in the variant form known as pagetoid reticulosis. Most cases display aberrant loss of the CD7 antigen. The finding of CD7 loss must be interpreted with caution, however, as some inflammatory dermatoses also contain significant populations of CD7- T-cells.

Molecular genetics: T-cell receptor gene rearrangements are generally detectable by PCR and/or Southern blot studies. Information regarding the cytogenetic findings in MF is limited by the difficulties of successful karyotypic analysis of small skin biopsies. Analysis of peripheral blood lymphocytes in patients with Sezary syndrome generally display complex karyotypes,117 but specific recurrent abnormalities have not been identified. Recent comparative genomic hybridization studies have suggested losses of chromosomes 1p and 17p may be common.118

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