Identification of patients with lymphocytic variant hypereosinophilic syndrome (L-HES) is challenging, and has important prognostic and therapeutic implications.

This study was undertaken to assess diagnostic tools for L-HES and to develop evidence-based diagnostic recommendations.

Biomarkers of T-cell-driven disease were compared between patients with L-HES versus idiopathic HES (I-HES) variants. Those performed routinely (serum immunoglobulin levels, T-cell phenotyping, T-cell receptor [TCR] gene rearrangement patterns) were collected from medical files, whereas others were prospectively assessed on stored blood samples (serum CCL17/thymus and activation regulated chemokine [TARC] levels, in vitro cytokine production).

This study included 48 patients with I-HES and 20 with L-HES associated with a CD3CD4 T-cell subset, including 7 with less than 5% aberrant cells. Neither increased serum immunoglobulin levels nor clonal TCR gene rearrangements were sufficiently sensitive or specific for L-HES. In contrast, systematically enhanced expression of the T-cell surface antigens CD2, CD5, CD45RO, and CD95 by these cells allowed for accurate detection by flow cytometry. Serum CCL17/TARC levels were significantly higher in patients with L-HES compared with those with I-HES, and a threshold of 3000 pg/mL allowed for detection of all subjects with L-HES with 75% specificity. Quantification of intracytoplasmic cytokine production by flow cytometry is the most reliable method for detection of enhanced type 2 cytokine expression, most notably for IL-4 and IL-13.

Adapting the standard of procedure for T-cell phenotyping in patients with unexplained hypereosinophilia is currently the most reliable means of identifying those with CD3CD4 L-HES.