Eosinophilia

Disease Description (Causes and Symptoms)

• Definition and criteria
  • Eosinophilia is a condition in which the eosinophil count in peripheral blood exceeds the normal range. It is generally defined as an absolute eosinophil count (AEC) ≥ 400–500 cells/µL, and is classified as mild (400–1,500/µL), moderate (1,500–5,000/µL), or severe (>5,000/µL).
• Main causes
  • Parasitic infections (particularly tissue-invasive roundworms), allergies and atopy, drug reactions, certain fungal infections, autoimmune and rheumatic diseases, hematologic malignancies (leukemia and lymphoma), idiopathic or primary eosinophilic disorders (e.g., hypereosinophilic syndrome, HES), adrenal insufficiency, etc.
• Summary of pathophysiology
  • Cytokines such as IL-5, IL-3, and GM-CSF induce eosinophil proliferation and activation in the bone marrow. Eosinophils then infiltrate tissues and cause tissue damage and inflammation through degranulation (including major basic protein and eosinophil cationic protein). In some cases, persistent proliferation occurs due to gene rearrangements such as PDGFRA.
• Main symptoms and organ involvement
  • Common symptoms: itching (pruritus), rash, cough and shortness of breath, generalized edema, fatigue, fever, and weight loss.
  • Major complications in severe cases: cardiac involvement (endocardial fibrosis, restrictive cardiomyopathy, and valvular damage), nervous system involvement (peripheral neuropathy, encephalopathy, and embolism), and respiratory, hepatic, gastrointestinal, and renal involvement.
  • Special form: When eosinophilia occurs with asthma, pulmonary infiltrates, and vasculitis, it may correspond to eosinophilic vasculitis (e.g., eosinophilic granulomatosis with polyangiitis, EGPA / Churg–Strauss).

Treatment

• General principles
  • Treatment for eosinophilia varies depending on whether it is symptomatic, whether there is organ involvement, and its cause. The underlying disease should be identified, and treatment of the cause (such as treatment of parasitic infection, discontinuation of a drug, or treatment of a tumor) should be prioritized.
• Drug treatment (main options)
  • Treatment of the cause: Appropriate anthelmintics for parasitic infections (e.g., albendazole or an agent appropriate for the type of parasite); discontinuation of the causative drug in drug-induced cases.
  • Acute/severe organ involvement or severe symptoms: Systemic corticosteroids (e.g., prednisone) — the dose and duration are determined according to the clinical situation.
  • Specialized treatments:
    • Primary eosinophilia/HES with a confirmed PDGFRA gene rearrangement: Tyrosine kinase inhibitors (e.g., imatinib) may be highly effective.
    • Severe or steroid-dependent/refractory HES and EGPA: Anti-IL-5 treatments (such as mepolizumab) are being used increasingly.
    • Cytotoxic agents (hydroxyamide/hydroxyurea, vincristine, and cyclophosphamide) or interferon-α may be considered in idiopathic or refractory cases.
• Procedures/surgery
  • Surgical treatment is generally uncommon, but surgical management may be necessary depending on complications (e.g., intestinal perforation).
• Lifestyle management and precautions
  • Do not take steroids long term without a doctor’s instructions; management of side effects is necessary.
  • Be sure to inform your doctor about travel to areas where parasites are prevalent or exposure to pets.
  • When starting a new medication, monitor for allergic reactions and side effects.
  • Seek emergency medical care immediately if cardiac symptoms (chest pain, fainting, or shortness of breath) or acute neurological symptoms (paralysis or decreased consciousness) occur.

Checklist Before an Outpatient Visit (Including Sample Questions)

• Items and documents to prepare
  • A list of all medications and supplements currently being taken (if possible, bring medication packets and prescriptions).
  • Previous test results (recent CBC/differential, chest X-ray/echocardiogram, etc.).
  • Travel history and place of residence (including possible exposure to poor sanitation or parasites), as well as a history of exposure to pets or livestock products.
  • The timing and course of symptom onset (including weight changes, fever, itching, and respiratory symptoms) and a record of when severe symptoms occurred.
  • If possible, urine and stool samples for stool testing (when parasite testing is recommended).
• Information to tell the doctor first at the outpatient visit
  • Whether acute chest pain, fainting, rapidly worsening shortness of breath, or acute neurological symptoms have occurred recently.
  • Any medications started recently (including prescription drugs, OTC medications, herbal medicines, and nutritional supplements) and a history of allergic reactions.
• Tips for preparing for tests
  • Blood tests (complete blood count and repeat AEC), peripheral blood smear, stool parasite testing (recommended at least twice), parasite serology/ELISA, ANCA (including MPO-ANCA), and parathyroid, thyroid, and adrenal function tests may be performed as needed. Depending on the situation, chest imaging, echocardiography, electrocardiography, pulmonary function tests, bone marrow testing, and genetic testing (such as FIP1L1–PDGFRA) may be recommended.

General Sample Questions to Ask the Doctor

• "What is my absolute eosinophil count (AEC), and how is its severity classified?"
• "Is there a risk that this condition will affect my organs, especially my heart or nervous system? What additional tests are needed?"
• "Are there any medications or infections suspected as the cause? Should I stop any of the medications I am taking?"
• "What treatment options are recommended, and what are the expected benefits and side effects of each?"
• "Once treatment begins, how often will follow-up testing be needed?"

Examples of Condition-Specific Questions

• If a parasitic infection is suspected: "Which parasites should be checked for in stool and serologic tests, and which antiparasitic medication is recommended if the diagnosis is confirmed?"
• If organ involvement (e.g., the heart) is suspected: "When should echocardiography, electrocardiography, and markers of myocardial injury (such as troponin) be performed to rule out cardiac involvement? If cardiac involvement is confirmed, how will the treatment plan change?"

Additional guidance: In cases of persistent or severe eosinophilia, or suspected unexplained decline in organ function (such as the heart or central nervous system), prompt specialist consultation (including hematology, allergy, cardiology, or neurology) and detailed testing are necessary.