OVERVIEW

What is eosinophilia?

Eosinophilia is characterized by a persistent increase in eosinophil count in the blood or bone marrow, along with significant eosinophil infiltration in tissues. It is often clinically associated with various diseases.

It represents a disease process, particularly a nonspecific response to parasitic infections, allergic diseases, connective tissue disorders, and tumors.

Eosinophilia is classified based on the degree of eosinophil elevation:

• Mild: Eosinophils (0.4–1.5)×10⁹/L;
• Moderate: Eosinophils (1.5–5)×10⁹/L;
• Severe: Eosinophils >5×10⁹/L.

Is eosinophilia common?

No, it is uncommon, occurring in approximately 1 in 100,000 hospitalized patients.

Who is more likely to develop eosinophilia?

It primarily affects individuals aged 20–50, though children and the elderly may also develop it. The male-to-female ratio is about 2:1.

SYMPTOMS

What are the manifestations of eosinophilia?

The clinical manifestations vary depending on the cause.

It may present as fever, bronchial asthma, urticaria, angioneurotic edema, abdominal pain, eczema, exfoliative dermatitis, dermatitis herpetiformis, pemphigus, psoriasis, pityriasis rubra, ichthyosis, pruritus, pigmentation, joint swelling and pain, etc.

• Eosinophilic dermatitis: More common in middle-aged and elderly men. Patients are generally in good condition with no systemic damage. Widespread polymorphic rashes are common, including erythema, papules, wheals, nodules, etc., with intense itching.
  Chronic cases may develop lichenified skin changes due to long-term scratching. Some patients may also experience fever, fatigue, superficial lymphadenopathy, and limb edema.

• Eosinophilic pneumonia: Presents with dry cough, low-grade fever, increased eosinophils in sputum, and migratory patchy shadows on chest X-ray.

• Eosinophilic gastroenteritis: Often related to food, accompanied by vomiting, abdominal pain, and diarrhea.

What other diseases can eosinophilia cause?

• Different causes may lead to different complications, such as asthma, urticaria, dermatitis herpetiformis, etc.

• Skin (including mucous membranes) erythema, edema/angioedema, ulcers, pruritus, and eczema.

• Fibrosis (in the lungs, heart, digestive tract, skin, and other organs/tissues).

What conditions should eosinophilia be differentiated from?

Eosinophilia needs to be differentiated from granulocytic sarcoma, eosinophilic angiomatous lymphoid hyperplasia, etc.

• Granulocytic sarcoma, also known as myeloid sarcoma, is a solid malignant tumor composed of immature granulocytes, often secondary to myeloid leukemia and more common in children and adolescents.
  It frequently involves flat and long bones, liver, spleen, lymph nodes, breast, gastrointestinal tract, skin, etc., and requires bone marrow aspiration for differentiation.

• Eosinophilic angiomatous lymphoid hyperplasia: This condition is more common in young adults, typically affecting the scalp and neck, and rarely other areas. Lesions appear as single or multiple subcutaneous or intradermal nodules, ranging from light red to dark red. Differentiation can be made based on blood tests, bone marrow aspiration, and pathological examination.

CAUSES

What are the causes of eosinophilia?

• Reactive eosinophilia:

  • Allergic: Bronchial asthma, allergic rhinitis, drug allergies, skin diseases, etc.;
  • Infections: Parasitic diseases, tuberculosis, chlamydia;
  • Skin diseases: Psoriasis, exfoliative dermatitis, eczema;
  • Connective tissue diseases: Rheumatoid arthritis, granulomatosis with polyangiitis, polyarteritis nodosa;
  • Tumors: Lymphoma, cystic fibrosis, etc.;
  • Endocrine diseases: Pituitary insufficiency, immunodeficiency disorders, IgA deficiency, graft-versus-host disease.

• Clonal eosinophilia: Chronic eosinophilic leukemia, myeloproliferative neoplasms, myelodysplastic syndromes, etc.

• Idiopathic hypereosinophilic syndrome: No specific cause can be identified.

• Others: Familial eosinophilia, radiation exposure, inflammatory bowel disease, eosinophilic cystitis, eosinophilic cholecystitis, eosinophilic meningitis, idiopathic hypereosinophilic syndrome.

DIAGNOSIS

How is eosinophilia diagnosed?

Eosinophilia can be diagnosed when the absolute eosinophil count in peripheral blood is elevated (eosinophils > 0.4×10⁹/L).

The key to this condition lies in identifying its underlying cause. Therefore, clinicians must conduct thorough examinations to determine the primary disease. Patients with uncertain diagnoses should undergo regular follow-ups.

What tests are required for patients with eosinophilia, and why?

Clinicians should obtain a detailed medical history and perform physical examinations to identify potential causes of eosinophilia.

• All patients with eosinophilia should undergo the following routine laboratory tests:

  • Complete blood count and peripheral blood smear differential count;
  • Standard biochemical tests, including liver and kidney function, electrolytes, and lactate dehydrogenase;
  • Erythrocyte sedimentation rate and/or C-reactive protein;
  • Serum vitamin B12;
  • Facial electromyography: Performed one week after onset to assess facial nerve damage and predict recovery.

• Patients with systemic symptoms or persistent eosinophilia (absolute eosinophil count ≥ 1.5×10⁹/L), with or without suspected organ involvement, should first undergo the following tests to confirm or rule out secondary causes:

  • For allergic causes: Serum IgE, allergen-specific IgE, and skin prick tests for specific allergies.
  • For non-allergic skin causes: Skin biopsy.
  • For infectious causes: Stool parasite and ova microscopy, serological tests for suspected parasitic infections, HIV, and human T-cell lymphotropic virus type 1 (HTLV-1).
  • For gastrointestinal causes: Upper gastrointestinal endoscopy, enteroscopy, or proctoscopy; serum amylase; serological tests for celiac disease-related autoantibodies.
  • For connective tissue diseases: Antinuclear antibody (ANA) or anti-double-stranded DNA antibody (dsDNA), cyclic citrullinated peptide (CCP) antibody.
  • For vasculitis: Anti-neutrophil cytoplasmic antibody (ANCA), serological tests for HBV, HCV, HIV, CMV, and B19 virus.
  • For respiratory diseases: Imaging studies, bronchoscopy.

• Patients with no identifiable secondary cause and eosinophilia (absolute eosinophil count ≥ 1.5×10⁹/L) should be evaluated for hematologic malignancies with clonal eosinophilia. The following tests are recommended to confirm or exclude possible diseases:

  • Bone marrow aspiration smear;
  • Bone marrow biopsy;
  • FISH or RT-PCR for FIP1L1-PDGFRA fusion gene;
  • Chromosomal karyotyping;
  • Serum mast cell tryptase;
  • T-cell immunophenotyping ± TCR gene rearrangement;
  • RT-PCR or sequencing to identify relevant fusion genes.

• If organ damage due to eosinophilia is suspected, the affected organs should be assessed:

  • Cardiac evaluation: Chest X-ray, electrocardiogram, echocardiogram, serum troponin T.
  • Pulmonary evaluation: Spirometry, oxygen saturation, and carbon monoxide transfer factor (TLCO).

TREATMENT

Which department should I visit for eosinophilia?

Dermatology, hematology, rheumatology, or oncology.

Does eosinophilia require hospitalization?

Patients with no obvious symptoms and a clear cause can be treated as outpatients with regular follow-ups based on the treatment plan. Patients with severe symptoms and an unclear cause should be hospitalized to identify the underlying condition and screen for hematologic, rheumatic, oncologic, or familial diseases.

How is eosinophilia treated?

• Treatment of eosinophilia should focus on addressing the underlying disease. If caused by parasitic allergies, removing the trigger is sufficient, and no special treatment is needed, with a good prognosis. If organ damage is present, treatment to reduce eosinophil counts or block their effects should be given, regardless of the degree of eosinophilia.

• Secondary eosinophilia mainly involves treating the primary disease. Primary or idiopathic eosinophilia generally requires treatment based on major organ involvement and dysfunction.

• Emergency treatment:

  • In cases of severe or life-threatening organ involvement, especially in the heart or lungs, emergency treatment is necessary. First-line therapy includes intravenous methylprednisolone at 1 mg/(kg·d) or oral prednisone at (0.5–1.0) mg/(kg·d). If eosinophilia is extreme, allopurinol should be added. Gradually taper the dose over 1–2 weeks, reducing to the minimal maintenance dose over 2–3 months.

  • Patients diagnosed with hereditary (familial) eosinophilia, primary (clonal) eosinophilia, or eosinophilia of undetermined significance (idiopathic) should seek immediate medical attention. Treatments such as imatinib, ruxolitinib, glucocorticoids, hydroxyurea, azathioprine, cyclosporine A, or antitumor drugs require hospitalization for detailed treatment planning, with timely adjustments based on response and efficacy.

  • For refractory or treatment-intolerant patients with an unknown cause, hematopoietic stem cell transplantation should be considered if a suitable donor is available and the patient's condition permits.

DIET & LIFESTYLE

What should patients with eosinophilia pay attention to in their diet?

If allergens can be identified, avoid consuming allergenic foods. Eat more vitamin-rich foods and minimize spicy or irritating foods.

What should patients with eosinophilia pay attention to in daily life?

• Keep warm, avoid catching cold or exposure to wind, maintain a regular routine, prevent excessive fatigue and insufficient sleep, and quit smoking and alcohol.

• Avoid allergenic foods and medications, and stay away from radioactive substances.

• Frequently air bedding to prevent parasites.

• Minimize contact with pets such as cats and dogs.

Does eosinophilia require follow-up examinations? How?

Yes. Typically, a follow-up blood test is conducted at the outpatient clinic. Since medications are mostly metabolized by the liver and kidneys, liver and kidney function tests should also be performed. Depending on secondary causes, additional tests may include serum IgE, rheumatism-related markers, and ANCA.

For patients with heart or lung involvement, further evaluations such as chest X-rays, electrocardiograms, echocardiograms, and serum troponin T tests should be conducted.

PREVENTION

Can eosinophilia be prevented?

Eosinophilia secondary to bronchial asthma, allergic rhinitis, drug allergies, parasitic infections, tuberculosis, etc., can be prevented. In daily life, exposure to relevant allergens should be avoided, as well as catching cold or being exposed to wind. Maintain a regular lifestyle, avoid excessive fatigue, and insufficient sleep.