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Eosinophil biology and causes of eosinophilia

Authors:

Peter F Weller, MD, FACP

Amy D Klion, MD

Section Editors:

Donald H Mahoney, Jr, MD

Bruce S Bochner, MD

Deputy Editors:

Alan G Rosmarin, MD

Anna M Feldweg, MD

Contributor Disclosures

All topics are updated as new evidence becomes available and our peer review process is complete.

Literature review current through: Nov 2016. | This topic last updated: Nov 03, 2015.

INTRODUCTION — Eosinophils are predominantly tissue-dwelling cells whose functions in health are not entirely understood. Eosinophils in the peripheral blood or tissues can increase in a wide array of disease states, ranging in severity from mild to life-threatening, and as a result of several mechanisms. When activated, eosinophils are capable of releasing mediators and substances that can damage tissues and contribute to disease pathology.

Normal eosinophil biology, the mechanisms of eosinophilia, tissue damage by eosinophils, and the major causes of eosinophilia are discussed in this topic review. An approach to the patient with eosinophilia and the diagnosis and management of the hypereosinophilic syndromes are reviewed separately. (See "Approach to the patient with unexplained eosinophilia" and "Hypereosinophilic syndromes: Clinical manifestations, pathophysiology, and diagnosis" and "Hypereosinophilic syndromes: Treatment".)

EOSINOPHIL BIOLOGY — Eosinophils are white blood cells (WBCs) of the granulocytic lineage, which also includes neutrophils and basophils [1]. The true physiologic function(s) of eosinophils remain largely unknown although they are likely involved in host immune response to infection, tissue remodeling, tumor surveillance, and maintenance of other immune cells [2]. Eosinophils develop and differentiate in the bone marrow under the influence of interleukin (IL)-5, IL-3, and granulocyte-macrophage colony-stimulating factor (GM-CSF) [3].

Normal levels — In peripheral blood, an absolute eosinophil count (determined by multiplying the total WBC count by the percentage of eosinophils) of 0 to 500/microL (1500/microL are relatively infrequent in this disorder. Marked eosinophilia, dramatic elevation of serum immunoglobulin E (IgE), recurrent infections, or other atypical features should prompt evaluation for other causes of eosinophilia. (See "Pathogenesis, clinical manifestations, and diagnosis of atopic dermatitis (eczema)".)

●Eosinophilic panniculitis – Eosinophilic panniculitis is characterized by a prominent eosinophil infiltration of subcutaneous fat [31]. Lesions often are nodular but may present as plaques or vesicles. This pathology is commonly associated with gnathostomiasis, leukocytoclastic vasculitis, and erythema nodosum [31-33]. Eosinophilic panniculitis can also develop in response to injected medications [34-36].

●Episodic angioedema with eosinophilia – Although blood eosinophilia does not usually accompany angioedema, the entity of episodic angioedema with eosinophilia (Gleich syndrome) is characterized by recurrent episodes of angioedema, urticaria, pruritus, fever, weight gain, elevated serum immunoglobulin M (IgM), and leukocytosis with marked blood eosinophilia. (See "Hypereosinophilic syndromes: Clinical manifestations, pathophysiology, and diagnosis", section on 'Episodic angioedema with eosinophilia (Gleich syndrome)'.)

●Kimura disease and angiolymphoid hyperplasia with eosinophilia – Kimura disease presents as large subcutaneous masses on the head or neck of East Asian males, whereas angiolymphoid hyperplasia with eosinophilia (also known as epithelioid hemangioma) occurs in all races and is characterized by generally smaller and more superficial lesions. Eosinophilia is common to both conditions, which are of unknown origin [37-39]. One report described a series of 21 cases of Kimura disease in the United States, the majority of which had eosinophilia [39]. The posterior auricular or cervical lymph nodes were most often involved. Consistent histologic features included follicular hyperplasia, eosinophilic infiltrates, and proliferation of postcapillary venules. Treatment usually consists of surgical resection. In addition, some case reports suggest a beneficial effect from glucocorticoids [40], the selective H1 receptor antagonistcetirizine [41], radiotherapy [42,43], topical tacrolimus [44], and thalidomide [45].

●Eosinophilic fasciitis – Eosinophilic fasciitis, also known as Shulman's syndrome, is characterized by symmetrical induration of the skin. The onset is typically acute, and findings include erythema, swelling, and induration of the extremities that is accompanied by eosinophilia in up to two-thirds of patients. A subacute course may also occur. The thickening and hide-bound quality of the affected skin is somewhat similar to that seen with the scleroderma-spectrum disorders. However, the irregular, woody, peau d'orange texture of eosinophilic fasciitis is distinct from the smooth, shiny skin surface seen in patients with systemic sclerosis or localized scleroderma (picture 5). Skin involvement most commonly occurs on the extremities, neck, and trunk. (See "Eosinophilic fasciitis".)

●Eosinophilic cellulitis – Eosinophilic cellulitis, also known as Wells syndrome, is marked by recurrent lesions on the extremities; blood eosinophilia is present in 50 percent of cases (picture 6) [46,47]. There are several different clinical variants [47]. Involved skin appears cellulitic but is not tender or warm; the diagnosis may be suspected when patients do not respond to appropriate antibiotic treatment for bacterial cellulitis. Histology of a lesion in the acute stage shows edematous dermis infiltrated by eosinophils in a perivascular pattern. In the chronic stage, distinctive "flame figures" composed of masses of collagen and intact and degranulated eosinophils may be seen [48]. The skin findings usually resolve in two to eight weeks. Wells syndrome may be idiopathic, drug-related, or associated with myeloproliferative, immunologic, or infectious disorders [49-51].

●Eosinophilic pustular folliculitis – Human immunodeficiency virus (HIV)-associated eosinophilic pustular folliculitis is characterized by recurrent, pruritic crops of discrete, erythematous, urticarial follicular papules and rare pustules, with a diameter of 3 to 5 mm (picture 7 and picture 8). The most common areas of involvement are the scalp, face, neck, and upper trunk; all are areas with a high concentration of sebaceous glands. It is found primarily in HIV-positive patients, patients undergoing treatment for hematologic malignancies and bone marrow transplant recipients [52]. However, it can also be seen in infants in a self-limited form [53]. (See "HIV-associated eosinophilic folliculitis".)

●Recurrent cutaneous necrotizing eosinophilic vasculitis – In this distinct vasculitis of small dermal vessels, skin biopsies show necrotizing vasculitis with minimal or absent leukocytoclasis and an almost exclusive eosinophilic infiltration in vessel walls and lumen [54-56]. Patients usually respond to systemic glucocorticoid treatment and pursue a chronic but relatively benign course.

●Eosinophilic ulcer of the oral mucosa – These ulcerated lesions appear to result from trauma, are usually tender and multiple, and often involve the tongue. Eosinophilic infiltration is prominent, and the lesions usually heal spontaneously over several weeks [57-60].

●Other dermatologic conditions – Tissue eosinophilia may be seen in blistering diseases such as bullous pemphigoid, pemphigus vulgaris, dermatitis herpetiformis, and herpes gestationis. Eosinophils or deposited eosinophil granule proteins can also be prominent in drug-induced lesions, chronic urticaria, solar urticaria, delayed pressure urticaria [61], the pregnancy-related dermatosis pruritic urticarial papules and plaques syndrome (PUPPS), and in orbital pseudotumors [62]. An uncommon disorder, characterized by the association of nodules, eosinophilia, rheumatism, dermatitis, and swelling (NERDS), includes prominent para-articular nodules, recurrent urticaria with angioedema, and tissue and blood eosinophilia [63].

Sinonasal and pulmonary — A variety of pulmonary diseases can be associated with eosinophilic inflammation of the airways and pleura. These are described briefly here and reviewed in detail elsewhere. (See "Causes of pulmonary eosinophilia" and "Tropical pulmonary eosinophilia" and "Pleural fluid eosinophilia"and "Chronic eosinophilic pneumonia".)

●Allergic rhinitis – Allergic rhinitis is a common disorder that presents with sneezing, rhinorrhea, and nasal congestion. If present, blood eosinophilia is usually mild to moderate. (See "Allergic rhinitis: Clinical manifestations, epidemiology, and diagnosis", section on 'Routine laboratory findings'.)  

●Chronic rhinosinusitis – Eosinophilia of involved tissues is frequent in several forms of chronic rhinosinusitis. Specific disorders that may be accompanied by blood and tissue eosinophilia include allergic fungal rhinosinusitis, chronic rhinosinusitis with nasal polyposis, often associated with aspirin sensitivity, and the sinusitis of eosinophilic granulomatosis with polyangiitis ([EGPA] previously called Churg-Strauss syndrome). (See "Allergic fungal rhinosinusitis" and "Chronic rhinosinusitis: Clinical manifestations, pathophysiology, and diagnosis", section on 'CRS with nasal polyposis' and "Aspirin-exacerbated respiratory disease" and "Clinical features and diagnosis of eosinophilic granulomatosis with polyangiitis (Churg-Strauss)".)

●Asthma – Asthma can cause eosinophilia, and other causes of eosinophilia (eg, helminthic infection, fungal infection) can present with bronchospasm mimicking asthma. Thus, it is helpful to establish the temporal relationship between development of asthma symptoms and eosinophilia, if possible. Helminthic infections that can cause wheezing are reviewed separately. (See "Causes of pulmonary eosinophilia", section on 'Transpulmonary passage of helminth larvae (Löffler syndrome)'.)  

Asthma-associated eosinophilia is usually mild to moderate (eg,  ................
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