What Are the Causes of Eosinophilia?

Eosinophilia is the technical name for an increased eosinophil count. Eosinophils are a type of white blood cells that destroy substances in the body like parasites and participate in allergic reactions. 

If you have eosinophilia, your symptoms will partially be determined by the cause of the elevated eosinophilia count. If your eosinophil count is mildly elevated you may not have any symptoms. Common symptoms include:

• Rash
• Itching
• Diarrhea, in the case of parasite infections
• Asthma
• Runny nose, particularly if associated with allergies

There are numerous reasons your eosinophil count may be elevated. Some of the causes are benign and require little treatment. It is not uncommon for the elevated count to be transient and resolve without treatment. Let's review some of the causes now.

• Parasite infections: Worldwide the most common cause of eosinophilia is a parasite infection. Names of these infections include schistosomiasis, trichinosis, strongyloidiasis, and ascariasis. These parasites can be found worldwide including the United States. Travel history is an important part of the work-up for eosinophilia although a lack of recent travel does not rule out parasitic infections. Travelers' diarrhea is a type of parasite infection but is not commonly associated with eosinophilia. 
• Drug reactions: Medications can trigger eosinophilia, sometimes without any obvious signs or symptoms. The most common medications associated with eosinophilia include antibiotics (penicillin, cephalosporins), non-steroidal anti-inflammatory medications (aspirin, ibuprofen), ranitidine (for gastroesophageal reflux), phenytoin (anti-seizure) and allopurinol (used to treat gout). The most severe form is called drug reaction with eosinophilia and systemic symptoms (DRESS). Fortunately, most people will not have these reactions when they receive these medications.
• Atopy: Atopy is a particular reaction that occurs in the body. Typically, atopy refers to asthma, seasonal allergies (also called allergic rhinitis), and eczema. It is not uncommon for someone to have more than one of these medical conditions as they are related. These are some of the most common causes of mild to moderate eosinophilia, particularly in children. Similarly, food allergies can also cause elevated eosinophil counts.
• Eosinophilia Esophagitis (EoE): This is a disorder characterized by eosinophils spreading to the esophagus which normally does not contain eosinophils. About 50% of people with EoE will also have elevated eosinophil counts in the blood.
• Hypereosinophilic Syndromes: Hypereosinophilic syndromes (HES) are a group of disorders characterized by very high eosinophil counts and evidence of organ damage from a large number of eosinophils. Organs commonly targeted are skin, lung, and gastrointestinal tract. HES can be primary (also called neoplastic) secondary (reactive) or idiopathic (cause unknown).  
• Churg-Strauss Syndrome: Churg-Stauss vasculitis, now called eosinophilic granulomatosis with polyangiitis, can cause eosiniophilia. People with this condition present with asthma and other lung issues initially, then develop eosinophilia, and eventually vasculitis, inflammation of the blood vessels. 
• Cancers: There are several cancers, particularly blood cancers, that are known for increasing the eosinophil count. These include a rare type of acute myeloid leukemia (AML) called eosinophilic leukemia. Other causes include several of the myeloproliferative neoplasms (such as essential thrombocythemia, polycythemia vera) B-cell and T-cell lymphoma, as well as adenocarcinomas of the gastrointestinal tract, lung, and cervix.

Like most blood disorders, eosinophilia is identified on complete blood count (CBC). Eosinophils are one of the white blood cells and are found in the portion of the CBC called the differential. The differential reports how many of each type of white blood cells (neutrophil, lymphocyte, monocyte, eosinophil, and basophil) are present in the blood.

After identification of eosinophilia, your healthcare provider will start working towards identifying the cause, sometimes this requires referral to a hematologist. Eosinophilia can be categorized by the number of eosinophils (absolute eosinophil count).

• Mild: 500 - 1500 cells/mL
• Moderate: 1500 - 5000 cells/mL
• Severe: > 5000 cells/mL

Determining the cause of your eosinophilia will be based on your symptoms. Eosinophilia esophagitis may cause difficulty swallowing, chest and/or abdominal pain, vomiting or food getting stuck in the esophagus. Diagnosis requires a biopsy of the esophagus. Many of the parasite infections are diagnosed by taking stool samples and testing them. There may not be a test to determine if a medication is the cause of your eosinophilia. If your eosinophil count returns to normal after discontinuing the medications, it is usually presumed that the medication was the cause. 

Similar to what diagnostic may be needed, treatment is determined by the cause of eosinophilia. Options include:

• Observation: If your eosinophilia is mild, observation with repeat labs may be recommended.
• If a medication is causing your elevated eosinophil count, it may be discontinued
• Maximizing therapy for asthma, eczema, and allergies
• Parasite infections are treated with anti-parasitic medications.
• Steroids such as prednisone may be used to treat hypereosinophilic syndromes

Hypereosinophilia is a scary-sounding word. Fortunately, for most people with this condition, it is transient and requires little to no treatment. For some, diagnosis and treatment may require referral to a specialist. If you have additional concerns, make sure to discuss them with your physician.