Eosinophilic Disorders
Eosinophils usually account for less than 7% of the circulating leukocytes (100 to 500 eosinophils per microliter of blood). These cells have a role in the protective immunity against certain parasites but also contribute to the inflammation that occurs in allergic disorders.
An increased number of eosinophils in the blood (eosinophilia) usually indicates the response of the body to abnormal cells, parasites, or substances that cause an allergic reaction (allergens). A low number of eosinophils in the blood (eosinopenia) can occur with Cushing's syndrome and stress reactions but does not usually cause problems because other parts of the immune system compensate adequately.
Idiopathic hypereosinophilic syndrome is a disorder in which the number of eosinophils increases to more than 1,500 cells per microliter of blood for more than 6 months without an obvious cause.
People of any age can develop idiopathic hypereosinophilic syndrome, but it is more common in men older than 50. The increased number of eosinophils can damage the heart, lungs, liver, skin, and nervous system. For example, the heart can become inflamed in a condition called Löffler's endocarditis, leading to formation of blood clots, heart failure, heart attacks, or malfunctioning heart valves.
Symptoms may include weight loss, fevers, night sweats, fatigue, cough, chest pain, swelling, stomachache, skin rashes, pain, weakness, confusion, and coma. Additional symptoms of this syndrome depend on which organs are damaged. The syndrome is suspected when the number of eosinophils is persistently increased in people who have these symptoms. The diagnosis is confirmed when a doctor determines that the eosinophilia is not caused by a parasitic infection, an allergic reaction, or another diagnosable disorder.
Without treatment, generally more than 80% of the people who have this syndrome die within 2 years; with treatment, more than 80% survive. Heart damage is the principal cause of death. Some people need no treatment other than close observation for 3 to 6 months, but most need drug treatment with prednisone or hydroxyurea. If these drugs fail, a variety of other drugs may be used, and they can be combined with a procedure to remove eosinophils from the blood (leukapheresis).
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