Discriminating clinical features

• Drugs: history of exposure, time course of eosinophilia with resolution on cessation of drug.

• Allergic conditions: history of eczema, urticaria or typical rashes. Symptoms and signs of asthma.

• Parasites: history of exposure from foreign travel, symptoms and signs of iron deficiency anaemia (hookworm is commonest cause worldwide). Blood film may show filariasis. Stool microscopy and culture for ova, cysts and parasites for amoebiasis, Ascaris, Taenia, schistosomiasis.

• Skin diseases: typical appearances confirmed by biopsy e.g. dermatitis herpetiformis and pemphigus.

• PAN: renal failure, neuropathy, angiography and ANCA positivity.

• Sarcoid: multi-system features with non-caseating granulomata in biopsy of affected tissue or on BM biopsy; high serum ACE.

• Hodgkin's: lymphadenopathy, hepatosplenomegaly—BM or node biopsy.

• Hypereosinophilic syndrome: history of allergy, cough, fever and pulmonary infiltrates on CXR, may be cardiac involvement. Eosinophils on blood film have normal morphology and granulation. Diagnosis on exclusion of similar causes.

• Eosinophilic leukaemia: eosinophils on blood film have abnormal morphology with hyperlobular and hypergranular forms. BM heavily infiltrated with same abnormal cells. Other signs of myeloproliferative disease may be present.

• AML M4Eo: blasts with myelomonoblastic features on BM and blood film (see p151).

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