What is the initial approach to evaluate and manage eosinophilia?

Initial Approach to Eosinophilia Workup

The evaluation of eosinophilia should follow a systematic approach based on geographical exposure history, symptom presentation, and degree of eosinophilia, with concentrated stool microscopy being the essential first-line investigation for all returning travelers and migrants with eosinophilia. 1

Definition and Classification

• Eosinophilia: Peripheral blood eosinophil count >0.45 × 10^9/L 1
• Severity classification:
  • Mild: >0.5 × 10^9/L
  • Moderate (hypereosinophilia): >1.5 × 10^9/L
  • Severe: >5.0 × 10^9/L 2

Initial Diagnostic Workup

Step 1: Laboratory Assessment

• Complete blood count with differential to confirm eosinophilia
• Peripheral blood smear to evaluate blood cell morphology
• Comprehensive metabolic panel with liver function tests
• Urinalysis with protein-to-creatinine ratio
• C-reactive protein
• Serum tryptase
• Vitamin B12 levels 2

Step 2: Travel and Exposure History

Obtain detailed information about:

• Geographic areas visited (helminth infections vary by region)
• Exact timing of possible exposures
• Activities: swimming in freshwater, walking barefoot
• Consumption patterns: drinking water, raw foods (salads, raw fish) 1

Step 3: Targeted Testing Based on Geography and Exposure

For returning travelers and migrants:

• All patients should undergo concentrated stool microscopy regardless of symptoms 1

For travelers/migrants from Africa:

• Schistosomiasis serology (especially with freshwater exposure)
• Strongyloides serology
• Filariasis serology
• Stool microscopy (3 samples)

For travelers/migrants from Asia:

• Strongyloides serology
• Filariasis serology
• Stool microscopy
• Consider Clonorchis/Opisthorchis serology if history of raw fish consumption 1

For travelers/migrants from Latin America:

• Strongyloides serology
• Stool microscopy
• Consider Trypanosoma cruzi serology 1

Clinical Syndromes to Recognize

Asymptomatic Eosinophilia

• Common in 12-81% of returning travelers and migrants 1
• Most common causes: intestinal helminths, schistosomiasis, strongyloidiasis, filariasis
• Multiple infections may coexist in up to 28% of cases 1

Katayama Syndrome (Acute Schistosomiasis)

• Occurs 2-9 weeks after freshwater exposure in Africa
• Presents with high-grade eosinophilia, fever, dry cough, urticarial rash
• May have abdominal pain, diarrhea, pulmonary infiltrates 1

Loeffler's Syndrome

• Associated with tissue migration phase of helminth infection
• Presents with transient pulmonary infiltrates, dry cough, wheeze 1

Important Considerations

Timing of Infection

• Eosinophilia may be transient during tissue migration phase
• Stool microscopy may be negative during prepatent period
• Eosinophilia often resolves when organisms reach gut lumen 1

Serological Testing

• Most serological tests become positive 4-12 weeks after infection
• Cross-reactivity is common (e.g., filarial serology may be positive in strongyloidiasis)
• Avoid requesting tests where epidemiology doesn't support diagnosis 1

Non-Infectious Causes to Consider

• Medications (NSAIDs, beta-lactams, nitrofurantoin)
• Allergic conditions (asthma, eczema, hay fever)
• Hematologic malignancies
• Connective tissue disorders 1

Follow-up and Monitoring

• If eosinophilia persists at ≥1.5 × 10^9/L for >3 months, refer to hematology
• Consider bone marrow aspirate and biopsy with immunohistochemistry
• For suspected hypereosinophilic syndrome, perform molecular testing for tyrosine kinase gene fusions (PDGFRA rearrangement) 2, 3
• Evaluate for organ damage with cardiac assessment (ECG, echocardiogram) in persistent cases 2

Treatment Approach

Treatment depends on identified cause:

• For parasitic infections: appropriate antiparasitic therapy
• For medication reactions: discontinue offending drug
• For allergic disorders: antihistamines, corticosteroids, allergen avoidance
• For hypereosinophilic syndrome with PDGFRA/B rearrangements: imatinib 2, 4
• For idiopathic hypereosinophilic syndrome: corticosteroids (prednisone 1 mg/kg/day) as first-line treatment 2

Common Pitfalls to Avoid

1. Failing to obtain concentrated stool microscopy in all returning travelers with eosinophilia
2. Overlooking Strongyloides infection, which can persist for decades and cause hyperinfection syndrome in immunocompromised patients
3. Requesting serological tests where epidemiology doesn't support diagnosis
4. Ignoring the timing of infection when interpreting negative stool microscopy results
5. Failing to recognize that normal blood eosinophil count doesn't exclude tissue eosinophilia 1, 2