What Causes Eosinophilia?

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Normally, eosinophils make up one to three percent of the peripheral blood leukocytes (i.e., circulating white blood cells), or 350 to 650 per cubic millimeter. Eosinophilia is defined as an abnormally high number of eosinophils in the blood. Eosinophilia is considered mild when there are less than 1,500 eosinophils per cubic millimeter, moderate with 1,500 to 5,000 per cubic millimeter, and severe if there are more than 5,000 eosinophils per cubic millimeter.

There are a number of possible causes and conditions associated with eosinophilia. The most common causes involve allergic conditions, infectious diseases, or neoplastic disorders (cancer). To pinpoint the cause, a patient's medical history and a physical examination are essential, especially for providing initial clues.

Medications are often behind allergic reactions. Any medication may be responsible, but usually antibiotics or nonsteroidal anti-inflammatory drugs (NSAIDs) are linked to peripheral eosinophilia. When allergic eosinophilic inflammation develops, rash, fever, and pulmonary infiltrates may occur.

Infectious causes are often suspected for patients who developed eosinophilia after traveling out of the country. Helminth infections are associated with eosinophilia. One such condition, called Loeffler's syndrome, is characterized by transient pulmonary infiltrates with eosinophilia in response to the passing of helminth larvae through the lungs. Fungal infections, other parasitic infections, and tuberculosis have also been associated with eosinophilia.

With regard to malignancy as a possible cause of eosinophilia, hematologic (blood) malignancies may be eosinophilic. With lymphoid neoplasms, there may be a reactive eosinophilia. Peripheral eosinophilia may also occur with solid organ malignancies.

Eosinophilia may also be associated with certain cases of connective tissue diseases, Sjogren's syndrome and rheumatoid arthritis. There are various autoimmune, inflammatory, or systemic conditions that may be related to eosinophilia. While these conditions are generally considered a less common cause for eosinophilia, the diagnostician must consider the possibility. Let's look at a few.

Eosinophilic Granulomatosis With Polyangiitis

Eosinophilic granulomatosis with polyangiitis, a condition formerly known as Churg-Strauss Syndrome, is classified as a systemic vasculitis. The disease, according to The Johns Hopkins Vasculitis Center, was first described in 1951 by Dr. Jacob Churg and Dr. Lotte Strauss as a syndrome that consisted of asthma, eosinophilia, fever, and "accompanying vasculitis of various organ systems."

Eosinophilic Fasciitis (aka Diffuse Fasciitis With Eosinophilia)

Eosinophilic fasciitis is a rare disorder in which the skin and the tissue beneath the skin become painful, inflamed, and swollen, with gradual hardening in the arms and legs. Diagnosis relies on biopsy of skin and fascia (the tough fibrous tissue on top of and between the muscles). Because of the characteristic hardening and thickening, it must be distinguished from scleroderma. Treatment of eosinophilic fasciitis typically involves the use of corticosteroids (usually oral prednisone). While the cause is not known, there seems to be a precipitating event involving exertion in many cases.

Eosinophilic Myalgia Syndrome

Eosinophilia myalgia syndrome is a disorder in which abnormally high numbers of eosinophils cause inflammation in nerve, muscle, and connective tissue. Along with pain, rash, swelling, cough, and fatigue, severe muscle pain that worsens is the chief complaint. The condition was first identified in 1989, after being linked to the health supplement, L-tryptophan. The supplement was banned but not before people died from it. There are cases of eosinophilic myalgia that are not related to L-tryptophan.

Hypereosinophilic Syndrome

Hypereosinophilic syndrome is characterized by peripheral blood eosinophilia, with greater than 1500 eosinophils per cubic millimeter that persists for six months or more, causing organ system involvement but without parasitic, allergic, or any other apparent cause of eosinophilia. Symptoms are dependent of which organs are involved. Diagnosis involves excluding other causes of eosinophilia, as well as bone marrow and cytogenetic testing. Treatment usually begins with prednisone.

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