Sezary syndrome is characterized clinically by pruritic erythroderma, generalized lymphadenopathy and the presence of circulating malignant T lymphocytes (Sezary cells) [1-3]. Other typical cutaneous changes include palmoplantar hyperkeratosis, alopecia and onychodystrophy . Differentiation from non-neoplastic erythroderma may be extremely difficult. The main causes of erythroderma, besides cutaneous T-cell lymphoma, are atopic dermatitis, psoriasis and drug reactions . Erythrodermic mycosis fungoides should be distinguished from true Sezary syndrome (see Chapter 2).
One of the major problems in Sezary syndrome is that variable diagnostic criteria have been used in different studies, which hinders comparison of clinicopathological and prognostic data. The presence of a monoclonal population of T lymphocytes within the peripheral blood has been recently proposed by the European Organization for Research and Treatment of Cancer (EORTC) Cutaneous Lymphoma Study Group, by the International Society for Cutaneous Lymphomas and by others as an important criterion for the diagnosis of Sezary syndrome [1,6-10]. Other useful criteria include the presence of more than 1000 circulating Sezary cells/mm ; an expanded CD4+ population in the peripheral blood resulting in a markedly increased CD4+: CD8+ ratio (> 10); an increased population of CD4+ : CD7- cells in the peripheral blood; Sezary cells larger than 14 |m in diameter; and Sezary cells representing more than 20% of circulating lymphocytes [1,2,10,11].
Although Sezary syndrome is regarded as the leukaemic variant of cutaneous T-cell lymphoma, involvement of the bone marrow is rare in the early phases but may be found at a later stage . The exact relation to mycosis fungoides is unclear, although some authors consider the two diseases as variations of the same entity (see Chapter 2). In 1975, the term 'cutaneous T-cell lymphoma' was introduced to encompass mycosis fungoides, Sezary syndrome and related disorders . The EORTC classification lists mycosis fungoides and Sezary syndrome as separate entities . By contrast, in the classification of tumours of the haematopoietic system proposed recently by the World Health Organization (WHO), Sezary syndrome, although listed separately, is discussed in a chapter together with mycosis fungoides, mentioning that 'the disease is by tradition regarded as a variant of mycosis fungoides' .
Patients usually present with an abrupt onset of erythroderma, or with erythroderma preceded by itching and a nonspecific skin rash. Rarely, a classic Sezary syndrome may develop in patients with preceding mycosis fungoides; it has been suggested to classify these cases as 'Sezary syndrome preceded by mycosis fungoides', as it remains unclear whether the clinical features and prognosis are similar . The presence of neoplastic T cells within the peripheral blood alone should not prompt a diagnosis of Sezary syndrome unless all other main diagnostic criteria are met .
The aetiology of Sezary syndrome is unknown. One case with a complex p53 gene mutation has been observed in a Chernobyl survivor, suggesting a possible relationship with environmental factors . The association with viral infections or previous long-standing dermatoses is unclear [14-16]. Much information on the neoplastic cells has been gathered by studies on tissue samples and cell lines. In most cases, so-called Sezary cells express a predominantly helper T-cell type 2 (Th2) cytokine profile, characterized by expression of interleukin 4 (IL-4), IL-5 and IL-10. Several genetic aberrations as well as aberrant antigen, cytokine or other molecular profiles have been documented in patients with Sezary syndrome, but the diagnostic and therapeutic implications of these findings are still unclear [17-31].
The TNM staging classification used for mycosis fungoides has also been adopted for Sezary syndrome. According to this system, Sezary syndrome is classified as stage III by definition (see p. 10).
Similarly to mycosis fungoides, patients with Sezary syndrome have an increased risk of developing second malignancies [32,33].
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