Steroid Resistant Hypereosinophilic Syndrome Suspected to Be Caused by Aberrant T-cell Subset

A 53-year-old male presented with cough, skin rash and lymphadenopathies complicated with hypereosinophilia (HE) in the blood, and patchy shadows in both lungs on chest computed tomography. Reactive causes for HE were excluded, and no clinical or laboratory features of myeloproliferative disorders could be found. HE caused by aberrant T-cell subsets was suspected because of serum hyper-immunoglobulin E level, and organ involvement of skin and lungs, though we could show neither aberrant T-cell surface markers nor T-cell receptor gene rearrangement. In the course of steroid monotherapy, tolerable maintenance dose could not be attained and the steroid-sparing agents of hydroxycarbamide, cyclosporine and interferon-α were introduced. However, the therapeutic response was inadequate, and organ involvement of lungs and intestinal tract developed. HE caused by aberrant T-cell subsets has steroid resistance and a risk of malignant transition, and we considered this progressive steroid refractoriness to be a sign of such a transition. Cytotoxic chemotherapy or bone marrow transplantation will likely be the next treatment modality in this patient.