Sézary syndrome

Sézary syndrome is a rare, aggressive form of cutaneous T-cell lymphoma (CTCL) derived from mature CD4+ helper T cells. It is considered the leukemic phase/variant of mycosis fungoides, though it can arise de novo. Pathophysiology involves malignant clonal expansion of CD4+ T cells with a memory/skin-homing phenotype (CLA+, CCR4+), which infiltrate the skin, blood, and lymph nodes.

Clinical triad: (1) diffuse erythroderma (generalized red, scaly, pruritic skin), (2) generalized lymphadenopathy, and (3) circulating atypical lymphocytes called Sézary cells—T cells with characteristic cerebriform (brain-like folded) nuclei seen on peripheral blood smear. Patients often have severe pruritus, alopecia, palmoplantar hyperkeratosis, and nail dystrophy. Immunophenotype is typically CD3+, CD4+, CD8-, with loss of CD7 and/or CD26 (useful for flow cytometry diagnosis).

Diagnosis requires skin biopsy showing epidermotropism with Pautrier microabscesses (collections of atypical lymphocytes in the epidermis), plus demonstration of a significant Sézary cell count in blood (absolute Sézary cell count ≥1000 cells/microL), an expanded CD4+/CD8+ ratio (>10), and/or evidence of a T-cell clone via TCR gene rearrangement studies (PCR or Southern blot) matching in skin and blood.

Staging follows the TNMB (tumor, node, metastasis, blood) system for CTCL. Sézary syndrome is classified as stage IVA or higher due to blood involvement.

Treatment options include skin-directed therapy (topical steroids, phototherapy with PUVA), systemic therapies such as extracorporeal photopheresis (ECP)—often first-line, retinoids (bexarotene), histone deacetylase inhibitors (vorinostat, romidepsin), interferon-alpha, and monoclonal antibodies (mogamulizumab targeting CCR4, brentuximab vedotin if CD30+). Allogeneic stem cell transplant may be considered in eligible patients for potential cure.

Prognosis is generally poor, with median survival of 2-4 years, worse than mycosis fungoides due to systemic involvement and associated immunosuppression predisposing to opportunistic infections, which are a common cause of death.

High-yield board points: Sézary cells with cerebriform nuclei on blood smear, association with mycosis fungoides, CD4+ T-cell origin, and the classic triad are frequently tested.