Lymph node involvement by mycosis fungoides and Sézary syndrome mimicking angioimmunoblastic T-cell lymphoma

Clinical management of cutaneous T-cell lymphoma (CTCL) and angioimmunoblastic T-cell lymphoma (AITL) differs markedly. Diagnostic distinction is critical. Herein, we describe a series of 4 patients with clinically, molecularly, and histopathologically annotated mycosis fungoides or Sézary syndrome whose nodal disease mimicked AITL. The patients otherwise exhibited classic clinical manifestations of mycosis fungoides/Sézary syndrome preceding the onset of lymphadenopathy by 1 to 5 years. Skin biopsies revealed epidermotropic infiltrates characteristic of CTCL. Lymph node biopsies revealed dense CD4+ T-cell infiltrates that coexpressed follicular helper T-cell markers and were accompanied by proliferations of high endothelial venules and arborizing CD21+ follicular dendritic cell networks. Two patients had T-cell receptor gene rearrangement studies performed on their skin, lymph node, and peripheral blood demonstrating identical polymerase chain reaction clones in all 3 tissues. A small secondary clonal B-cell population was present in 1 patient that mimicked the B-cell proliferations known to accompany AITL and persisted on successive nodal biopsies over several years. This latter phenomenon has not previously been described in CTCL. The potential for patients to be misdiagnosed with AITL for lack of consideration of advanced-stage CTCL with nodal involvement underscores the necessity of information sharing among the various pathologists and clinicians involved in the care of each patient.