The main functions of eosinophils include involvement in defense against parasites, allergic responses, tissue inflammation and immunity. Eosinophilia is defined as a peripheral eosinophil count greater than 0.44 x 10⁹/L. In many cases the cause is clear, e.g. atopic disease. However, the differential diagnosis includes many serious diseases, including malignancy.

Epidemiology

• In the UK, eosinophilia is most often due to allergic conditions.
• Worldwide, helminth infections are the most common cause of eosinophilia.

Presentation

• Travel history to assess whether a patient has travelled to an area that is endemic for certain infections, including helminthic infections.
• Medication and diet history to evaluate for allergic reactions associated with eosinophilia.
• History of symptoms associated with possible underlying causes (see Causes below).
• A complete physical examination is required because diseases associated with eosinophilia can involve any part of the body.

Causes

• Allergy diseases: asthma, urticaria, eczema, allergic rhinitis, drug hypersensitivity, angioneurotic oedema
• Connective tissue diseases: Churg-Strauss syndrome, rheumatoid arthritis, eosinophilic fasciitis, polyarteritis nodosa, eosinophilia myalgia syndrome
• Infections:
  • Convalescence from any infection
  • Ascariasis, schistosomiasis, trichinellosis, visceral larva migrans, strongyloidiasis, echinococcosis, coccidioidomycosis
  • Human T-cell lymphotropic virus I (HTLV-I)
• Hypereosinophilic syndrome
• Neoplasia:
  • Lymphoma (e.g. Hodgkin's lymphoma, non-Hodgkin's lymphoma)
  • Leukaemia: chronic myeloid leukaemia, adult T-cell leukaemia/lymphoma (ATLL), eosinophilic leukaemia (very rare)
  • Gastric cancer or lung carcinoma (i.e. paraneoplastic eosinophilia)
• Endocrine: adrenal insufficiency, e.g. Addison's disease
• Skin disease - pemphigus, dermatitis herpetiformis, erythema multiforme
• Löffler's syndrome
• Löffler's endocarditis (restrictive cardiomyopathy with eosinophilia)
• Irradiation
• Post-splenectomy
• Cholesterol emboli
• Drugs, e.g. penicillins, streptomycin

Investigations

• Full blood count, including differential white cell count, renal function tests, liver function tests.
• Urine tests: all patients with blood eosinophilia and haematuria and who have been in Africa should have their urine examined for the eggs of Schistosoma haematobium. Cystoscopy may be required to confirm the diagnosis.
• Lumbar puncture: CSF eosinophilia due to worm infections (e.g. Angiostrongylus cantonensis), drug reactions, and coccidioidomycosis meningitis.
• CT scans of the lungs, abdomen, pelvis, and brain evaluate for focal defects due to diverse causes of eosinophilia, e.g:
  • Worm infections of the liver (e.g. Fasciola hepatica) can cause focal hepatic lesions.
  • Coccidioidomycosis can cause focal lesions in the lung, which are visible on a chest X-ray or CT scan.
  • Hodgkin's or non-Hodgkin's lymphoma can cause lymphadenopathy in the abdomen, which can be seen on a CT scan.
• Echocardiogram to assess for thrombi (e.g. mural, endocardial) due to hypereosinophilic syndrome.
• Bone marrow biopsy may be required.

Internet and further reading

• Liss M; Eosinophilia; eMedicine; May 2009.
• Peter Weller; Oxford Textbook of Medicine 4th edition; Section 22.35.

Acknowledgements