Mycosis fungoides is an indolent, CD4+ cutaneous T-cell lymphoma that presents on the skin. It is characterized by scaly, pruritic, well-demarcated skin plaques and patches that are refractory to initial treatment. In the later stages of the disease, mushroom-shaped tumors develop within the plaque lesions, and ultimately lymphadenopathy and hepatosplenomegaly can develop. Mycosis fungoides, which is based on the fungus-like growth pattern of the lesions, is misleading as the disease is not fungal in origin. Histopathological evidence is essential for diagnosis and typically consists of atypical lymphocytes found in the upper dermis or aggregates of such cells within the epidermis (known as Pautrier microabscesses). Early treatment consists of topical glucocorticoids, while treatment for later stages involves a combination of localized radiation, electron beam therapy, and systemic chemotherapy. Sézary syndrome, a cutaneous T-cell lymphoma with leukemic dissemination of mutated T cells can be an advanced form of mycosis fungoides or arise de novo.
- Approx. 4% of non-Hodgkin lymphoma cases
- Mycosis fungoides and Sézary syndrome are the two most common cutaneous T-cell lymphomas (CTCL).
- Age: mostly middle-aged or elderly patients
- Sex: ♂ > ♀
Epidemiological data refers to the US, unless otherwise specified.
- Initially, pruritic cutaneous plaques, patches, and brownish nodules develop. 
- Subsequently, systemic spread occurs, including lymphadenopathy and hepatosplenomegaly.
- Atypical CD4+ T-cells with cerebriform nuclei (from clumped chromatin) infiltrating the dermis and epidermis
- Pautrier microabscesses: aggregates of atypical CD4+ T-cells within the epidermis that are indicative of the disease 
- Definition: a cutaneous T-cell lymphoma with leukemic dissemination of mutated T cells
- Exact prevalence unknown
- Can be an advanced form of mycosis fungoides or arise de novo
Systemic skin lesions
- Erythroderma accompanied by palmar and plantar hyperkeratosis
- Intense pruritus
- Generalized lymphadenopathy
- Systemic skin lesions
- Diagnostics: : based on the characteristic triad of pruritic erythroderma, lymphadenopathy, and atypical T cells (Sézary cells) on peripheral blood smear 
The leukemic dissemination present in Sézary syndrome distinguishes it from mycosis fungoides.
Adult T-cell leukemia (ATL) 
- Definition: a non-Hodgkin lymphoma associated with infection with the human T-cell lymphotropic virus I (HTLV-I)
- Rare in the US; most commonly seen in Japan, West Africa, and the Carribean
- Associated with IV drug use
- Generalized lymphadenopathy
- Skin lesions: may be similar to those seen in mycosis fungoides
- Lytic bone lesions
- Peripheral blood smear: lymphocytes with condensed chromatin and hyperlobulated nuclei that resemble clover leaves
- Laboratory tests: hypercalcemia, ↑ LDH
- Immunophenotype: stain positive for CD2, CD4, CD5, CD29, and CD45RO
- Initial lesions of mycosis fungoides can be confused with eczema due to the erythematous and pruritic patches or plaques.
- Mycosis fungoides is less likely to respond to initial treatment for eczema (including topical glucocorticoids).
The differential diagnoses listed here are not exhaustive.
Treatment for early stage disease 
- Topical corticosteroids (first-line)
- Topical nitrogen mustard (second-line)
Treatment for moderate to late stage disease 
- Total electron skin beam therapy (TSEBT)
- Systemic chemotherapy (e.g., bexarotene)
- Topical corticosteroids may also be used.