The hypereosinophilic syndrome is a sustained elevation in this count above 1.5 × 109/L (i.e. 1,500/μL) that is also associated with evidence of eosinophil-based tissue injury.
Diagnosis of eosinophilia is via a complete blood count (CBC), but diagnostic procedures directed at the underlying cause vary depending on the suspected condition(s).
Eosinophils represent a small percentage of peripheral blood leucocytes (usually less than 8%), have a half-life in the circulation of only 8–18 hours, but persist in tissues for at least several weeks.
[6][7] Eosinophils are one form of terminally differentiated granulocytes; they function to neutralize invading microbes, primarily parasites and helminthes but also certain types of fungi and viruses.
In conducting these functions, eosinophils produce and release on demand a range of toxic reactive oxygen species (e.g. hypobromite, hypobromous acid, superoxide, and peroxide) and they also release on demand a preformed armamentarium of cytokines, chemokines, growth factors, lipid mediators (e.g. leukotrienes, prostaglandins, platelet activating factor), and toxic proteins (e.g. metalloproteinases, major basic protein, eosinophil cationic protein, eosinophil peroxidase, and eosinophil-derived neurotoxin).
These agents serve to orchestrate robust immune and inflammatory responses that destroy invading microbes, foreign tissue, and malignant cells.
When overproduced and over-activated, which occurs in certain cases of hypereosinophilia and to a lesser extent eosinophilia, eosinophils may misdirect their reactive oxygen species and armamentarium of preformed molecules toward normal tissues.
These genes code for dysfunctional protein products capable of enhancing proliferation and/or survival of their parent cells which, in consequence, become an evolving and constantly growing clone of eosinophils.
For this diagnosis, immature eosinophil (e.g. myeloblast) cell counts in the bone marrow and peripheral blood must be less than 20% and the chromosomal alterations (inv(16)(p13.1q22)) and t(16;16)(p13;q22) as well as other features diagnostic of acute myelogenous leukemia must be absent.
[5][18] The idiopathic hypereosinophilic syndrome is a disorder characterized by hypereosiophilia that is associated with eosinophil-based tissue or organ damage.
While almost any organ or tissue may be damaged, the lung, skin, heart, blood vessels, sinuses, kidneys, and brain are the most commonly affected.
[5][7] Secondary (or reactive) eosinophilias are non-clonal increases in blood eosinophil levels caused by an underlying disease.
[citation needed] Helminths are common causes of hypereosinophilia and eosinophilia in areas endemic to these parasites.
Helminths infections causing increased blood eosinophil counts include: 1) nematodes, (e.g. Angiostrongylus cantonensis and Hookworm infections), ascariasis, strongyloidiasis trichinosis, visceral larva migrans, Gnathostomiasis, cysticercosis, and echinococcosis; 2) filarioidea, e.g. tropical pulmonary eosinophilia, loiasis, and onchocerciasis; and 3) flukes, e.g. schistosomiasis, fascioliasis, clonorchiasis, paragonimiasis, and fasciolopsiasis.
Drug- induced hepatitis marked by immunoallergic pathology, which has much bidirectional crossover with DRESS syndrome, is typically accompanied by some severity of eosinophilia.
Other drugs and drug classes often reported to cause increased blood eosinophil levels accompanied by less severe (e.g. non-DRESS syndrome) symptoms include tetracyclins, doxycycline, linezolid, nitrofurantoin, metronidazole, carbamazepine, phenobarbital, lamotrigine, valproate, desipramine, amitriptyline, fluoxetine, piroxicam, diclofenac, ACE inhibitors, abacavir, nevirapine, ranitidine, cyclosporin, and hydrochlorothiazide.
Other types of lymphoid malignancies have been associated with eosinophilia, as in lymphoblastic leukemia with a translocation between chromosomes 5 and 14 or alterations in the genes which encode platelet-derived growth factor receptors alpha or beta.
The disorder is clonal with regard to the production of abnormal T-cell lymphocytes not eosinophils which appear phenotypically normal.
In on study of 16 lymphocyte-variant hypereosinophilia patients with the aberrant CD3 negative, CD41 positive immunophenotype, good responds to corticosteroid drugs were uniform but 16 ultimately required corticosteroid-sparing agents.
Hydroxyurea and imatinib are less likely to have efficacy in this variant of hypereosinophilia than in many cases of clonal eosinophilia or chronic eosinophilic leukemia.
Similar to lymphocyte-variant hypereosinophilia, the increased levels of blood eosinophils in Gleich's syndrome is thought to be secondary to the secretion of eosinophil-stimulating cytokines by a T cell clones.
[29] Angiolymphoid hyperplasia with eosinophilia is a disorder initially classified as a form of IgG4-related diseases but now considered a distinct entity.
The tumors consist of histiocytoid endothelial cells prominently infiltrated by lymphocytes and eosinophils and is associated with hypereosinophilia or eosinophilia.
Affected tissues exhibit acute inflammation involving eosinophils, neutrophils, monocytes, lymphocytes, and plasma cells.
[31] A class of steroid hormones secreted by the adrenal gland, glucocorticoids, inhibit eosinophil proliferation and survival.
[32] Hypereosinophilia may occur in the setting of damage to a single specific organ due to a massive infiltration by eosinophils.
Other examples of organ-restricted hepereosinophilia include those involving the heart, kidney, liver, colon, pulmonary pleurae, peritoneum, fat tissue, myometrium, and synovia.
During an allergic reaction, the release of histamine from mast cells causes vasodilation which allows eosinophils to migrate from the blood and localize in affected tissues.
Eosinophils, like other granulocytes, contain granules (or sacs) filled with digestive enzymes and cytotoxic proteins which under normal conditions are used to destroy parasites but in eosinophilia these agents can damage healthy tissues.
[3] Elevated serum B12 or low white blood cell alkaline phosphatase, or leukocytic abnormalities in a peripheral smear indicates a disorder of myeloproliferation.