Spontaneous Resolution of Hypereosinophilic Syndrome in an Infant Without TreatmentHerrero, Blanca MD; de la Fuente, Jorge Ruiz PharmD; Aleo, Esther MD, PhD; Carceller, Fernando MD; Lassaletta, Álvaro MD; Orellana, Manuel Ramírez MD, PhD; Pérez-Martínez, Antonio MD, PhDJournal of Pediatric Hematology/Oncology: August 2012 - Volume 34 - Issue 6 - p 450–452 doi: 10.1097/MPH.0b013e318249579b Clinical and Laboratory Observations Abstract Author Information We report on a 4-month-old boy with hypereosinophilic syndrome (HES) and spontaneous progressive resolution without treatment. Differential diagnosis excluded myeloproliferative, lymphocytic, familiar, associated, and overlap HES. The final diagnosis was undefined HES. Repeated measurements of blood eosinophil counts, monitoring of clonal T cells, and observation of skin lesions and organ involvement were carefully performed as an outpatient. Departments of *Hemato-Oncology and Stem Cell Transplantation †Clinical Analysis, Hospital Infantil Universitario Niño Jesús, Madrid, Spain The authors declare no conflict of interest. Reprints: Antonio Pérez-Martínez, MD, PhD, Servicio de Hemato-Oncología y Trasplante Hematopoyético, Av. Menéndez Pelayo 65, Madrid 28009, Spain (e-mail: firstname.lastname@example.org). Received May 31, 2011 Accepted January 3, 2012 Copyright © 2012 Wolters Kluwer Health, Inc. All rights reserved.