Q&A: Causes Of Eosinophilia

Peripheral blood eosinophilia (≥500 eosinophils/microL) may be caused by numerous conditions, including allergic, infectious, inflammatory, and neoplastic disorders. The cause of eosinophilia is best identified by the patient's history, clinical presentation, and specific laboratory testing, and it is important to be aware of the absolute eosinophil count (AEC). The evaluation should seek to identify the cause of eosinophilia and assess the patient for associated organ involvement.

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In this article:
Eosinophils
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

Eosinophils

Eosinophils are white blood cells (WBCs) of the granulocytic lineage, which also includes neutrophils and basophils. The physiologic functions of eosinophils are incompletely understood, but they are involved in host immune response to infection, tissue remodeling, tumor surveillance, and maintenance of other immune cells. 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).

In peripheral blood, an absolute eosinophil count (determined by multiplying the total WBC count by the percentage of eosinophils) of 0 to 500 cells/microL (<0.5 x 109/L) is typically considered normal.

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.

MCQ exam: clinical scenario

The following are recognised causes of eosinophilia:

a). Malaria
b). Visceral leishmaniasis
c). Churg-Strauss syndrome
d). Drug hypersensitivity
e). Visceral larva migrans (toxocariasis)

MCQ exam: answer

The correct answer is F F T T T.
Churg-Strauss syndrome, drug hypersensitivity, and visceral larva migrans (toxocariasis) all cause eosinophilia.

MCQ exam: explanation

The upper limit of normal for eosinophils is usually taken to be 0.4x10⁹/l. The causes of eosinophilia may conveniently be divided into two groups: parasitic and nonparasitic. In general protozoal infections do not produce eosinophilia. Helminths do cause eosinophilia and the degree of eosinophilia is related to the extent of tissue invasion by the helminth. Filarial worms often cause a high eosinophilia whereas the intestinal nematodes tend to cause only a modest increase in the eosinophil count.

Important parasitic causes of eosinophilia include:

• Filarial worms
• Tapeworms
• Strongyloidiasis
• Hydatid disease
• Hookworm
• Fascioliasis
• Toxocariasis (visceral larva migrans)
• Schistosomiasis
• Trichinella spiralis
• Intestinal nematodes
• Tropical pulmonary eosinophilia(usually results from hypersensitivity to microfilariae)

Reference(s)
1). UpToDate: Eosinophil biology and causes of eosinophilia. Available online: https://www.uptodate.com/contents/eosinophil-biology-and-causes-of-eosinophilia