Mycosis fungoides is a cutaneous T-cell lymphoma that begins on the skin and may involve only the skin for years or decades. It may progress to systemic disease, including Sézary syndrome (erythroderma with circulating malignant T cells).
Localized or generalized erythematous scaly patches or plaques are present usually on the trunk. Plaques are almost always over 5 cm in diameter. Pruritus is a frequent complaint and can be severe. IL-31 may mediate the pruritus of Sézary syndrome. The lesions often begin as nondescript or nondiagnostic patches, and it is not unusual for the patient to have skin lesions for more than a decade before the diagnosis can be confirmed. Follicular involvement with hair loss is characteristic of mycosis fungoides, and its presence should raise the suspicion of mycosis fungoides for any pruritic eruption. In more advanced cases, tumors appear. Lymphadenopathy may occur locally or widely. Lymph node enlargement may be due to benign expansion of the node (dermatopathic lymphadenopathy) or by specific involvement with mycosis fungoides.
The skin biopsy remains the basis of diagnosis, though at times numerous biopsies are required before the diagnosis can be confirmed. In more advanced disease, circulating malignant T cells (Sézary cells) can be detected in the blood (T-cell gene rearrangement test). Eosinophilia may be present.
Mycosis fungoides may be confused with psoriasis, drug eruption, photoallergy, an eczematous dermatitis, or tinea corporis. Histologic examination can distinguish these conditions.
The treatment of mycosis fungoides is complex. Early and aggressive treatment has not been proven to cure or prevent disease progression. Skin-directed therapies, including topical corticosteroids, topical mechlorethamine, bexarotene gel, and UV phototherapy, are used initially. If the disease progresses, PUVA plus retinoids, PUVA plus interferon, extracorporeal photopheresis, bexarotene, histone deacetylase inhibitors (romidepsin or vorinostat), targeted immunomodulators (brentuximab, mogamulizumab), and total skin electron beam treatment are used.
Mycosis fungoides is usually slowly progressive (over decades). Prognosis is better in patients with patch or plaque stage disease and worse in patients with erythroderma, tumors, and lymphadenopathy. Survival is not reduced in patients with limited patch disease. Elderly patients with limited patch and plaque stage disease commonly die of other causes. Overly aggressive treatment may lead to complications and premature demise.
et al. Mycosis fungoides and Sézary syndrome: an update. Hematol Oncol Clin North Am. 2019 Feb;33(1):103–20.
et al. Guidelines for phototherapy of mycosis fungoides and Sézary syndrome: a consensus statement of the United States Cutaneous Lymphoma Consortium. J Am Acad Dermatol. ...