What are the causes and treatments of eosinophilia?

Causes and Treatment of Eosinophilia

Eosinophilia is caused by a wide range of conditions including parasitic infections, allergic disorders, drug reactions, neoplastic disorders, and autoimmune diseases, with treatment directed at the underlying cause. 1

Definition and Classification

• Eosinophilia is defined as a peripheral blood eosinophil count >0.5 × 10⁹/L
• Severity classification:
  • Mild: >0.5 × 10⁹/L
  • Moderate: >1.5 × 10⁹/L
  • Severe: >5.0 × 10⁹/L 1

Major Causes of Eosinophilia

1. Parasitic Infections

• Helminth infections - most common cause globally:
  • Schistosomiasis (Schistosoma spp.) 2, 1
  • Strongyloidiasis (Strongyloides stercoralis) 1
  • Hookworm infections 1
  • Toxocariasis (Toxocara canis and T. cati) 2
  • Cutaneous larva migrans (Ancylostoma braziliense and A. caninum) 2
  • Onchocerciasis (Onchocerca volvulus) 2
  • Filariasis 1
  • Baylisascaris procyonis 2
  • Paragonimiasis 2

2. Allergic Disorders

• Asthma
• Allergic rhinitis
• Atopic dermatitis
• Food allergies
• Drug allergies 1

3. Hematologic/Neoplastic Disorders

• Primary (clonal) eosinophilia:
  • Chronic eosinophilic leukemia (CEL)
  • Myeloid/lymphoid neoplasms with eosinophilia and gene rearrangements (PDGFRA, PDGFRB, FGFR1, PCM1-JAK2) 3, 4
• Secondary to other malignancies:
  • Hodgkin lymphoma
  • Non-Hodgkin lymphoma
  • Acute lymphoblastic leukemia 4

4. Drug-Induced Eosinophilia

• Common culprits:
  • Antibiotics (especially beta-lactams)
  • Antiepileptics
  • NSAIDs
  • Allopurinol 1

5. Autoimmune/Inflammatory Disorders

• Eosinophilic granulomatosis with polyangiitis (EGPA/Churg-Strauss syndrome)
• Connective tissue disorders
• Inflammatory bowel disease 3

6. Organ-Specific Eosinophilic Disorders

• Eosinophilic esophagitis
• Eosinophilic gastroenteritis
• Eosinophilic pneumonia 1

7. Hypereosinophilic Syndrome (HES)

• Idiopathic HES (diagnosis of exclusion)
• Lymphocyte-variant HES (T-cell clone-driven) 4

8. Other Causes

• Endocrine disorders (Addison's disease)
• Immunodeficiency syndromes
• Radiation exposure 5

Treatment Approach

1. Parasitic Infections

• Schistosomiasis: Praziquantel 40 mg/kg twice daily for 5 days 1
• Strongyloidiasis: Ivermectin 200 μg/kg/day for 1-2 days 1
• Hookworm: Albendazole 400 mg daily for 3 days 1
• Cutaneous larva migrans: Ivermectin 200 μg/kg single dose or Albendazole 400 mg daily for 3 days 2, 1
• Toxocariasis: Albendazole for 3-4 weeks ± corticosteroids 2

2. Allergic Disorders

• Allergen avoidance
• Antihistamines
• Corticosteroids (topical or systemic)
• Leukotriene modifiers 1

3. Eosinophilic Esophagitis

• First-line: Topical steroids
• Proton pump inhibitors
• Dietary modifications
• Endoscopic dilatation for strictures 1

4. Hypereosinophilic Syndrome

• First-line: Corticosteroids
• Steroid-refractory cases: Hydroxyurea and interferon-α
• Targeted therapy: Mepolizumab (IL-5 antagonist) for idiopathic HES 1, 4

5. Clonal Eosinophilia

• FIP1L1-PDGFRA or PDGFRB rearrangements: Imatinib (highly effective) 4, 6
• Aggressive forms: Cytotoxic chemotherapy and hematopoietic cell transplantation 4

6. Drug-Induced Eosinophilia

• Immediate withdrawal of the causative medication 1

Monitoring and Follow-up

• Regular monitoring of blood counts to confirm resolution
• For persistent eosinophilia, monitor for end-organ damage, particularly cardiac complications
• Follow-up complete blood counts for mild and transient eosinophilia 1

Important Considerations

• Delayed treatment of persistent hypereosinophilia can lead to irreversible organ damage
• Cardiac complications are particularly concerning
• For patients with travel history to tropical/subtropical regions, parasitic infections should be high on the differential diagnosis
• Serological tests for parasitic infections may not become positive until 4-12 weeks after infection 1