Lymphocytic Variant Hypereosinophilic Syndrome: Case Series From a Tertiary Referral Center in Canada.

BACKGROUND

Lymphocytic variant hypereosinophilic syndrome (L-HES) is a rare disorder characterized by persistent eosinophilia driven by aberrant T-cell populations. Diagnosis remains challenging due to the lack of standardized diagnostic criteria.

METHODS

We retrospectively analyzed 18 patients diagnosed with L-HES between 2016 and 2023. Comprehensive flow cytometry was performed on peripheral blood samples.

RESULTS

Nine patients demonstrated the classic sCD3-CD4+CD5+CD2+CD45RO+CD45RA- immunophenotype, ranging from 0.6% to 70% of total lymphocytes. Two patients showed variant sCD3-CD4+ phenotypes, five had expanded (> 10%) sCD3+CD4+CD7- T-cells, and two displayed aberrant CD8+ T-LGL populations. Clonality was established in all patients with nonclassic phenotypes by molecular TCR testing or based on uniform TRBC1. We assessed a serial gating strategy to quantify the classic L-HES phenotype and found this to be highly sensitive and specific with an estimated limit of detection of 0.06% of lymphocytes. Using this strategy, we identified decreased but detectable abnormal T-cells in all classic phenotype patients reassessed posttreatment, down to as low as 0.3% of lymphocytes. The identification of T-LGL phenotypes with eosinophilia is a novel finding.

CONCLUSION

Our study highlights the diverse immunophenotypic spectrum of L-HES, emphasizing the importance of comprehensive flow cytometry analysis for accurate diagnosis.