Mycosis fungoides is the most common cutaneous lymphoma (50%) but is still very uncommon. Radiotherapy often plays a role in its management. Distinguished from Sézary syndrome by a much more indolent course, better response to treatment, and lack of circulating Sézary cells in the blood.
Most cases present in the elderly or adults; the disease has been seen in younger age groups. Worldwide, the incidence is about 0.3-1 per 100,000 people per year; the disease is twice as common in men than in women.
Aetiology and Pathogenesis
The aetiology of mycosis fungoides is unknown
The lesions seen in mycosis fungoides are caused by a circulating population of dermatotrophic (skin-seeking) T-lymphocytes.
Mycosis fungoides is typically an indolent disease:
- Early stages present with patches of erythema
- These patches may develop into plaques as the disease progresses
- Eventually tumours begin forming within the skin, which may ulcerate
- Late in disease progression the tumour begins involving lymph nodes
- The final stage of disease occurs when visceral involvement develops
There are no 'premalignant' lesions known for mycosis fungoides.
Presentation depends on the stage of disease.
Symptoms and Signs
Patients usually present complaining of skin symptoms which may have been present for years - the average time for development of lesions to diagnosis is about 6 years. Lesions may be painful, itchy or ulcerated. Rarely, the disease may present with generalised erythroderma but lack the number of cerebriform cells in the bloodstream for a diagnosis of Sézary syndrome.
The earliest lesions are patches, non-elevated erythematous regions that represent infiltration by the T-lymphocytes. Plaques are raised lesions that are also erythematous, with poorly defined borders. Tumours of the skin are raised lumps that may be ulcerated. Examination may uncover peripheral lymphadenopathy in advanced cases.
It is important to exclude Sézary Syndrome, a variant of mycosis fungoides that presents rapidly with generalised erythema and circulating Sézary cells in the blood. This is accomplished by a simple blood test and counting of the cell numbers.
Imaging of the abdomen and pelvis should be performed when advanced disease is suspected; imaging of the chest is also warranted.
Biopsies of suspected mycosis fungoides lesions should be taken. This is important to confirm diagnosis of the disease, which can be elusive.
The macroscopic appearance of mycosis fungoides has been described above.
Biopsies of patches shows infiltration of the basal layer of epidermis by haloed lymphocytes. Plaques show an increased number of lymphocytes, often including cerebriform lymphocytes that tend to exist in the epidermis. Tumours may show further infiltration of the dermis. If over 25% of lymphocytes are large, transformation is suspected and the patient is at higher risk of lymph node involvement.
Usually: CD2+, CD3+, CD4+, CD5+ and TCRβ +, with CD7 and CD8 negativity.
Rarely CD8+ may be seen, particularly in paediatric cases. Cutaneous lymphocyte antigen is commonly seen.
There are no specific genetic changes that have been identified.
Unlike other lymphomas, mycosis fungoides and Sézary syndrome are not staged with Ann Arbor; instead, a unique staging system is used:
|IA||Patches, papules or plaques limited to < 10% of skin surface|
|IB||Patches, papules or plaques covering > 10% of skin surface|
|IIA||Patches, papules or plaques associated with early lymph node involvement (N1-2, see next table)|
|IIB||One or two skin tumours, no nodes|
|III||Erythroderma, with no nodal involvement, and < 1,000/μl circulating Sézary cells|
|IV||High blood tumour burden (> 1,000/μl), extensive lymph node involvement (N3+) or visceral disease|
|N1||Dermatopathic lymphadenopathy, no atypical cerebriform cells|
|N2||Dermatopathic lymphadenopathy, clusters of cerebriform cells with preservation of architecture|
|N3||Partial effacement of nodal architecture by cerebriform cells|
|N4||Complete effacement of architecture by cerebriform cells|