Mycosis fungoides

At a Glance

Mycosis fungoides is a form of primary cutaneous T-cell lymphoma. Mycosis fungoides is characterized by evolution of skin patches, plaques, and tumors, which often prompt a skin biopsy.

The histologic diagnosis is difficult in the early stages of mycosis fungoides. Skin biopsies classically show epidermotropic (lymphocytes infiltrating the epidermis) neoplastic T lymphocytes, with a dermal lymphoid infiltrate of varying intensity. Immunohistochemical stains for T-cell antigen expression on the skin biopsy may be helpful and classically demonstrate the lymphocytes to be CD4 positive but CD7 negative. Paraffin embedded tissue may be sent for T-cell receptor gene rearrangement detection by polymerase chain reaction (PCR) to prove the clonality/neoplastic nature of the T cells. The presence of histologic transformation, defined as greater than 25% large lymphoid cells, which may also be CD 30 positive, should also be assessed.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Patients will typically be referred to dermatologists or oncologists specialized in the treatment of cutaneous T-cell lymphomas. Mycosis fungoides may be an indolent disease. The most important factors for prognosis are the extent of cutaneous disease and extracutaneous spread, the detection of histologic transformation as described, and other indicators of tumor burdens, such as serum LDH.

Clinical staging systems incorporate pathologic assessment of clinically suspicious lymph nodes (>1.5 cm, involving excisional biopsies), for the number of abnormal lymphocytes: none, scattered atypical and large lymphocytes with cerebriform nuclei, or clusters and sheets of cells with replacement of lymph node architecture. Quantitation of neoplastic T lymphocytes within the peripheral blood (Sezary cells) is also performed, either by manual differential, flow cytometry, or both. A count of 1000 cells per micrometer is the cutoff between clinical stages III and IV. A more aggressive histologic variant of mycosis fungoides, “folliculotropic mycosis fungoides,” predominantly involves the head and neck.