Hypereosinophilia (HE) is rare but often secondary to a nonhematologic disease such as allergic disorders and parasitic infections. HE can also be associated with hematologic malignancies and be the result of a clonal proliferation or reactive to another hematologic condition. Association of HE with acute lymphoblastic leukemia (ALL) is rare in children. We reported a case of a teenager presented with HE secondary to B-ALL who experienced severe cardiac complications with severe absolute eosinophil count. We compared his clinical evolution with other published cases and we reported 2 mutations linked to B-ALL never described before in this context.

Case Study A seven-year-old boy was admitted to the emergency service for left elbow pain after a fall. On examination, his left elbow was swollen with limited movements and pain centered on the fifth ray. Diagnostic workup was completed with radiographs (Figure 1). The lateral view showed a positive fat pad sign due to joint effusion (arrows). On the frontal view, medial soft tissue swelling was noticed (arrowheads). Correct alignment between the bones was present on lateral and front views. Capitellum (C) and radius (R)