Eosinophilia

Written by M Y Karim, lecturer in immunology

What are eosinophils?

An eosinophil is a type of white blood cell.

Eosinophils are produced in the bone marrow and are normally found in the bloodstream and the gut lining. They contain proteins that help the body to fight infection from parasitic organisms, such as worms. But in certain diseases these proteins can damage the body.

What is eosinophilia?

The term eosinophilia refers to conditions in which abnormally high amounts of eosinophils are found in either the blood or in body tissues.

When does eosinophilia occur?

Eosinophilia occurs in a wide range of conditions. Its commonest causes in the UK are allergic diseases such as asthma and hay fever, whereas worldwide the main cause is parasitic infection. It can also occur in relation to common skin diseases, medicine reactions, and parasitic infections. Other rarer causes include:

lung diseases, eg Loeffler's syndrome

vasculitis (inflammation of blood vessels), eg Churg-Strauss syndrome

some tumours, eg lymphoma

liver cirrhosis

some antibody deficiencies; not typically AIDS

other rarer skin diseases, eg dermatitis herpetiformis

uknown causes, labelled hypereosinophilic syndrome.

How does eosinophilia occur?

Increased numbers of eosinophils are produced to fight off allergic disease or parasitic infections. This is helpful in combating parasitic infections but not in cases of allergic diseases as they accumulate in tissues and cause damage. For example, in asthma, eosinophilia causes damage to the airways of the lung.

What are the symptoms of eosinophilia?

The symptoms of eosinophilia are those of the underlying condition. For example, eosinophilia due to asthma is marked by symptoms such as wheezing and breathlessness, whereas parasitic infections may lead to abdominal pain, diarrhoea, fever, or cough and rashes.

Medicine reactions often give rise to skin rashes, and they often occur after taking a new drug.

Rarer symptoms of eosinophilia can include weight loss, night sweats, lymph node enlargement, other skin rashes, and numbness and tingling due to nerve damage.

Hypereosinophilic syndrome

Hypereosinophilic syndrome is a condition where there is no apparent cause for eosinophilia.

This rare condition can affect the heart, resulting in heart failure with breathlessness and ankle swelling, cause enlargement of the liver and spleen, resulting in swelling of the abdomen, and give rise to skin rashes.

How is eosinophilia diagnosed?

Eosinophilia in the bloodstream is diagnosed from a simple blood test. Tissue eosinophilia is diagnosed by the examination of the relevant tissue. For example, a piece of skin tissue can be removed (a skin biopsy) and examined under a microscope.

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