Prevalence and spectrum of T-cell lymphoproliferative disorders in patients with Hypereosinophilia: A reference laboratory experience.

Hypereosinophilia (HE) is defined as persistently elevated absolute eosinophil count (AEC) ≥ 1.5 × 109/L, which can be due to a variety of underlying causes. In this study, we investigated the prevalence and spectrum of T-cell lymphoproliferative disorders in 124 consecutive patients with HE by flow cytometric immunophenotyping. Available medical records, pathology reports and T-cell receptor (TCR) gene rearrangement were reviewed. Fifteen patients (12%) with HE had abnormal T-cell populations that were initially detected by flow cytometry. The presence of immunophenotypically abnormal T cells was not associated with higher AEC or higher absolute lymphocyte count levels, in comparison to those without abnormal T cells. Molecular studies concordantly identified a clonal TCR gene rearrangement in 8 of 10 cases tested. Based on the combination of clinical presentation, morphologic findings and laboratory studies, seven patients were diagnosed with the lymphocytic variant of hypereosinophilic syndrome and five with overt T-cell lymphoma (4 peripheral T-cell lymphoma NOS, 1 primary cutaneous T-cell lymphoma). The remaining three had an unknown diagnosis due to lack of information and additional workup would be warranted. These findings underscore the importance of flow cytometry as a screening tool to identify T-cell lymphoproliferative disorders in patients with HE.