An eosinophil is a type of white blood cell produced in the bone marrow and is 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. The term eosinophilia refers to conditions in which abnormally high amounts of eosinophils are found in either the blood or in body tissues.
Eosinophilia occurs in a wide range of conditions. In modern countries, its commonest causes 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 and drug reactions. Other rarer causes include: lung diseases, eg Loeffler's syndrome, vasculitis (inflammation of blood vessels), eg Churg-Strauss syndrome, some tumors, e.g. lymphoma, liver cirrhosis, some antibody deficiencies (not typically AIDS), other rarer skin diseases, eg dermatitis herpetiformis and other unknown causes, labeled hypereosinophilic syndrome.
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.
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, diarrhea, 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.
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. If your doctor cannot make a diagnosis, then you may be referred to a hematologist.
Further tests may include blood tests to measure levels of antibodies, stool examination, chest X-ray, CT scans of the chest and abdomen, skin or lung biopsies, examination of the bone marrow, and bronchoscopy.
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. In hypereosinophilic syndrome there is a high risk of damage to the heart and other major organs. In some cases a blood cell tumor known as a T-cell lymphoma may also develop, so patients must be carefully monitored.
The conventional treatment for hypereosinophilic syndrome is oral corticosteroid therapy. In most cases, when the cause of eosinophilia is identified, treatment significantly reduces the symptoms of the condition. Corticosteroids, both local (inhaled, topical), and systemic (oral, intramuscular, intravenous), are used to manage several allergic conditions and reduce the number of eosinophils.
In one review of 225 North American outpatients with eosinophilia [Brigden & Graydon 1997] the breakdown of causes was:
The causes for various degrees of eosinophila are along these lines:Mild
- Allergic rhinitis
- Hay fever
- Extrinsic asthma
- Drug reaction
- Parasitic disease
- Parasitic disease
- Intrinsic asthma
- Drug reaction
- Pulmonary eosinophilia syndrome
- Visceral Larva Migrans (Toxocara Canis/Cati)
- Tissue migration larval-stage helminths (roundworms)
- Hypereosinophilic syndromes
An excellent summary of the causes of eosinophilia can be found on this page