Interferon-α treatment of six patients with the idiopathic hypereosinophilic syndrome

Objective: To examine the response to interferon-α2B therapy in six patients with the idiopathic hypereosinophilic syndrome. Design: Prospective cohort study. Setting: Tertiary referral center, university hospital inpatient and outpatient clinics, and offices of private practice physicians. Patients: Six patients satisfying the criteria for the hypereosinophilic syndrome, five of whom were resistant to or intolerant of conventional treatment. Intervention: Individualized dosages of interferon-α based on clinical response and side effects. Measurements: Measurements of eosinophilia (peripheral and bone marrow counts), levels of serum eosinophil major basic protein, doses of glucocorticoid and cytotoxic medications, and transfusion requirements. Results: Various dosages of interferon-α from 1.5 MU/d to 8 MU/d decreased the total eosinophil count to less than 1000/mm³ in five of six patients. All patients were able to taper and discontinue prednisone and hydroxyurea. Both patients with incapacitating mucosal ulcers had resolution and no recurrence of these previously resistant lesions. Interferon-α was generally well tolerated except for dose-limiting side effects, including thrombocytopenia in one patient and in a second patient, temporary worsening of mucosal lesions and constitutional symptoms. Conclusions: Interferon-α is a valuable agent for patients with the hypereosinophilic syndrome who are resistant to or intolerant of conventional therapy and for patients with this syndrome who have incapacitating mucosal ulcers.