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Peter F. Weller

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date: 29 April 2017

Eosinophilia (eosinophil count >0.45 × 109/litre) is associated with some infections, some allergic diseases, and a variety of other conditions, often neoplastic.

Infectious diseases

Parasitic diseases—eosinophilia is a characteristic feature of infection by multicellular helminth parasites, e.g. Strongyloides stercoralis, with diagnosis typically based on geographical/dietary history and examination of stool for ova and larvae.

Other diseases—eosinophilia can be caused by the fungal disease coccidioidomycosis, and modest eosinophilia (0.45–1.5 × 109/litre) may accompany viral infections such as HIV and HTLV-1.

Allergic, immunological, neoplastic, and other disorders

Common allergic diseases—asthma, rhinitis, and atopic dermatitis are associated with modest eosinophilia.

Drug reactions—these are a frequent cause of eosinophilia, often in reactions characterized by rashes and pyrexia. More severe reactions may also manifest with (1) pulmonary eosinophilia and lung infiltrates; (2) interstitial nephritis; (3) hepatitis; (4) myocarditis; (5) drug-induced hypersensitivity vasculitis; (6) gastroenterocolitis; and (7) drug-induced rash, eosinophilia and systemic symptoms (DRESS syndrome).

Other conditions—these include (1) Churg–Strauss syndrome; (2) hyper-IgE syndrome—comprising recurrent staphylococcal abscesses, dermatitis, hyperimmunoglobulinaemia E, and eosinophilia; (3) chronic myeloid leukaemia, acute myeloblastic leukaemia (some types), Hodgkin’s disease (some types); (4) a variety of pulmonary, skin, gastrointestinal and endocrine diseases.

Hypereosinophilic syndromes

These are defined by (1) sustained eosinophilia (>1.5 × 109/litre), (2) lack of an identifiable cause precipitating a secondary eosinophilia, and (3) symptoms and signs of organ involvement. About 30% of patients will have either a myeloproliferative condition (chronic eosinophilic leukaemia) or hypereosinophilia mediated by clonal expansion of specific T cells producing interleukin 5 (IL-5).

Clinical features—common manifestations are (1) cardiac—endomyocardial damage typically leads to a restrictive cardiomyopathy; (2) neurological—strokes related to thromboemboli, encephalopathy, and polyneuropathy; (3) dermatological—e.g. angiooedema, urticarial lesions; (4) pulmonary—infiltrates of eosinophils may be seen in any part of the lung, sometimes leading to pulmonary fibrosis.

Treatment—patients without organ damage do not require treatment. Aside from supportive care (1) chronic eosinophilic leukaemia—may respond to tyrosine kinase inhibitors, e.g. imatinib; (2) nonmyeloproliferative hypereosinophilic syndrome—may respond to high-dose corticosteroids, with hydroxyurea, interferon-α‎ and anti-IL-5 monoclonal antibody (mepolizumab) used in refractory cases.

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