The idiopathic eosinophilia syndromes are a heterogeneous group of diseases which are characterized by a persistent eosinophilia > 1.5 x 109/L for more than six months with tissue lesions. The diagnosis is established after excluding other causes of an eosinophilia. Hypereosinophilic syndrome must be differentiated from other secondary reasons of eosinophilia (parasites, fungal and viral infections, allergic states, hematological and non-hematological neoplasms, drugs, rheumatoid diseases). BCR-ABL must be negative. If blasts are increased and clonality of the eosinophils can be proved, the diagnosis is chronic eosinophilic leukemia.
Hypereosinophilic syndromes like other states with eosinophilia can manifest with urticaria, fever, cough, shortness of breath, diarrhea or peripheral neuropathy. Tissue infiltration can lead to chronic congestive cardiomyopathy with valvular change and thickening of the endocardium with mural thrombi.
Eosinophils look normal for the most part. Often, however, they are also hypogranular and vacuolated with hyposegmented or hypersegmented nuclei. Additionally, anemia, anisocytosis, poikilocytosis, basophilia, thrombocytopenia or thrombocytosis as well as neutrophilia can occur.
Cellularity of the bone marrow is usually increased. The number of eosinophilic elements is variable and can be just above the normal (>7%) or constitute the majority of all nuclear elements. Cytologically. the eosinophilic cells are mostly inconspicuous. Scanning the bone marrow, special attention should be given to other causes of eosinophilia, such as parasites (e.g. leishmania), infiltrations of solid tumors, hints for myeloproliferative neoplasms or myelodysplastic syndromes, an increase of blasts, lymphocytic infiltrations and signs of systemic mastocytosis.