hematology and oncology
Eosinophilia
Introduction
Eosinophilia is defined as a peripheral blood eosinophil count>500/mcL (> 0.5 × 109/L). Causes and associated disorders are myriad but often represent an allergic reaction or a parasitic infection. Eosinophilia can be reactive (secondary) or the primary manifestation of a hematologic disorder. Diagnosis involves selective testing directed at clinically suspected causes. Treatment is directed at the cause. invokes a primary response with relatively low levels of eosinophils, whereas repeated exposures result in an augmented or secondary eosinophilic response. Several compounds released by mast cells and basophils induce IgE-mediated Eosinophil Production and Function . Such substances include eosinophil chemotactic factor of anaphylaxis, leukotriene B4, complement complex (C5-C6-C7), and histamine (over a narrow range of concentration). Peripheral eosinophilia is characterized as Mild: 500 to 1500/mcL (0.5 to 1.5 × 109/L) Moderate: 1500 to 5000/mcL (1.5 to 5 × 109/L) Severe: > 5000/mcL (> 5 × 109/L) Mild eosinophilia itself does not cause symptoms, but levels≥1500/mcL (≥ 1.5 × 109/L) may cause organ damage if they persist. Organ damage typically occurs because of tissue inflammation and reaction to the cytokines and chemokines released by the eosinophils as well as to immune cells that are recruited to the tissues. Although any organ may be involved, the heart, lungs, spleen, skin, and nervous system are typically affected (for manifestations, see table). Occasionally, patients with very severe eosinophilia (eg, eosinophil counts of>100,000/mcL [> 100 × 109/L]), usually with eosinophilic leukemia, develop complications when eosinophils form aggregates that occlude small blood vessels, causing tissue ischemia and microinfarctions. Manifestations typically include those of brain or lung hypoxia (eg, encephalopathy, dyspnea, respiratory failure). Hypereosinophilic Syndrome is a condition characterized by peripheral blood eosinophilia with manifestations of organ system involvement or dysfunction directly related to eosinophilia in patients who do not have a parasitic or allergic disorder, a clonal disorder of hematopoiesis, or another cause of eosinophilia. 