Itchy Skin: A Challenging Differential Diagnosis Between Mycosis Fungoides and Sézary Syndrome

Primary cutaneous lymphomas represent a diverse spectrum of T-cell and B-cell lymphomas with their primary skin manifestation. Among these, mycosis fungoides (MF) and Sézary syndrome (SS) represent classic forms of cutaneous T-cell lymphomas (CTCLs). This report details the case of a 67-year-old female who presented with longstanding pruritic skin lesions, initially misdiagnosed and managed as eczema. The diagnostic process ultimately revealed the presence of Sézary cells in the peripheral blood smear (PBS). The SS diagnosis was confirmed based on CD4 positivity and CD7 negativity as determined by flow cytometry. The disease was staged as IVA1 (T2N0M1B2). The patient exhibited partial improvement with oral corticosteroid therapy. This report underscores the critical importance of integrating clinical evaluation and blood findings to distinguish between MF and SS. The progression of a circulating clone signals a poor prognosis, requiring surveillance and consideration of targeted therapies to enhance patient outcomes and improve their quality of life. Early detection remains paramount in the management of these rare cutaneous lymphomas, which are associated with unique therapeutic challenges.