What is the recommended workup for hypereosinophilia?

Hypereosinophilia Workup

Begin by confirming hypereosinophilia (≥1.5 × 10⁹/L eosinophils on two examinations at least 1 month apart) and immediately assess for end-organ damage, as this constitutes a medical emergency requiring urgent corticosteroids before completing the diagnostic workup 1, 2.

Initial Assessment Priority

The workup must first distinguish between life-threatening and non-urgent presentations:

• Emergency evaluation needed if: Evidence of cardiac involvement (troponinemia, elevated NT-proBNP, abnormal echocardiogram), neurologic deficits, or any signs of end-organ damage 2
• Urgent corticosteroids: Start immediately if end-organ damage suspected—do not delay for complete diagnostic workup 2

Systematic Diagnostic Algorithm

Step 1: Exclude Secondary (Reactive) Causes

For returning travelers/migrants, helminths are the most common identifiable cause (19-80% of cases) 1:

• Stool examination: Three samples for ova and parasites
• Helminth serology: First-line test for strongyloides, schistosoma, filaria
• Filarial testing: Only for patients with West Africa exposure (day/night blood films no longer recommended as first-line) 1
• Geographic-specific testing: Based on travel history

For all patients, systematically exclude 1, 3:

• Medications: Review all current and recent drugs (common cause)
• Allergic conditions: Asthma, eczema, hay fever (most common in non-endemic areas) 1
• Autoimmune diseases: ANCA testing for EGPA, consider IgG4 levels
• Infectious diseases: HIV, fungal infections, parasites beyond helminths

Step 2: Evaluate for Primary (Neoplastic) Causes

If secondary causes excluded, proceed with hematologic workup 2, 4:

Blood and bone marrow evaluation:

• Complete blood count with differential
• Peripheral blood smear review
• Bone marrow aspirate and biopsy with morphologic assessment
• Flow cytometry for immunophenotyping

Molecular/genetic testing (critical for treatment decisions) 2, 4:

• PDGFRA rearrangements (especially FIP1L1-PDGFRA fusion)
• PDGFRB rearrangements
• FGFR1 rearrangements
• PCM1-JAK2 fusion
• BCR-ABL1 (if features suggest CML)
• T-cell receptor gene rearrangement studies (for lymphocytic variant)

Cytogenetics:

• Standard karyotype
• FISH for specific fusion genes

Caveat: Finding somatic mutations doesn't automatically indicate neoplastic disease—clonal hematopoiesis of indeterminate potential (CHIP) occurs in 20-25% of idiopathic cases and must be interpreted with bone marrow morphology 5.

Step 3: Assess for End-Organ Involvement

Cardiac evaluation (most critical organ system) 2:

• Troponin, NT-proBNP
• Electrocardiogram
• Echocardiogram
• Consider cardiac MRI if abnormalities detected

Other organ systems 1, 2:

• Pulmonary: Chest imaging, pulmonary function tests if symptomatic
• Neurologic: Clinical examination, imaging if deficits present
• Dermatologic: Skin biopsy if lesions present
• Gastrointestinal: Endoscopy with biopsy if symptoms present

Classification After Workup

Based on findings, classify as 2, 4:

1. Myeloid/lymphoid neoplasm with eosinophilia and TK fusion (MLN-eo-TK): PDGFRA/PDGFRB/FGFR1 rearrangements identified
2. Chronic eosinophilic leukemia (CEL): Blast phase or clonal markers without TK fusions
3. Lymphocytic variant HES: Aberrant T-cell clone identified
4. Secondary (reactive) HES: Underlying condition identified with end-organ damage
5. Idiopathic HES: No cause identified after complete workup, with end-organ damage
6. HE of undetermined significance (HE-US): No cause identified, no end-organ damage

Special Populations

Asymptomatic patients >24 months with travel history 1:

• Consider empirical treatment with albendazole 400 mg single dose plus ivermectin 200 μg/kg single dose after initial testing

Persistent eosinophilia ≥1.5 × 10⁹/L for >3 months without end-organ damage 1:

• Refer to hematology after infectious causes excluded or treated

Critical Pitfalls to Avoid

• Don't assume allergy alone causes hypereosinophilia: Eosinophilia >1.5 × 10⁹/L is rarely explained by allergy and always requires further workup 3
• Don't delay corticosteroids if cardiac involvement suspected: Cardiac damage is irreversible and potentially fatal 2
• Don't miss PDGFRA/PDGFRB rearrangements: These respond dramatically to imatinib 100-400 mg daily with high cure rates 2, 4
• Don't overlook Strongyloides: Can cause fatal hyperinfection syndrome if immunosuppressed later 1
• Don't interpret somatic mutations as definitive neoplasia: Requires correlation with bone marrow morphology 5