What is a hallmark of Sezary syndrome?

Sezary syndrome is a type of cutaneous T-cell lymphoma, specifically a leukemic form of mycosis fungoides. A key feature of this condition is the presence of malignant T cells in the blood. These atypical T cells typically have proliferative and neoplastic characteristics, contributing to both the diagnosis of the syndrome and the associated clinical manifestations, which include erythroderma, lymphadenopathy, and circulating leukemic cells.

The malignant T cells in Sezary syndrome can be detected through blood tests and are characterized by a distinct phenotype, often displaying aberrant expression of various surface markers. This hallmark is critical for diagnosing Sezary syndrome and differentiating it from other conditions that might present with skin lesions or systemic symptoms.

In contrast, the other options do not characterize Sezary syndrome as effectively. While high immunoglobulin levels or abnormal monocyte counts might be present in various conditions, they are not definitive indicators of Sezary syndrome. Severely decreased T cells would imply a different type of immunodeficiency or hematologic disorder rather than the neoplastic proliferation of T cells seen in this syndrome.