How is eosinophilia evaluated and treated?

Evaluation and Treatment of Eosinophilia

For patients with eosinophilia, begin with a detailed travel and exposure history to identify helminth infections (the most common identifiable cause in travelers/migrants), then proceed with stool microscopy and serology for specific parasites based on geographic exposure, while simultaneously evaluating for common non-infectious causes including allergic/atopic disorders and medications. 1, 2

Initial Diagnostic Approach

Define the Severity

• Mild eosinophilia: 0.5-1.5 × 10⁹/L 1
• Hypereosinophilia: >1.5 × 10⁹/L 1, 3
• Critical threshold: ≥1.5 × 10⁹/L for >3 months requires hematology referral after excluding/treating infectious causes 1, 2

Essential History Elements

• Travel history: Geographic regions visited help narrow differential (West Africa for filariasis, Africa for schistosomiasis, Southeast Asia for strongyloidiasis) 1
• Timing of exposure: Eosinophilia may be transient during tissue migration phase of helminth infections 4
• Medication review: NSAIDs, beta-lactam antibiotics, and nitrofurantoin are common culprits 4
• Atopic history: Asthma, eczema, allergic rhinitis, and food allergies account for ~80% of secondary eosinophilia in non-endemic regions 4, 5
• Gastrointestinal symptoms: Dysphagia or food impaction suggests eosinophilic esophagitis 1, 2

First-Line Laboratory Testing

• Stool microscopy (concentrated specimens) for helminth eggs 1, 2
• Serology for helminths based on travel history (note: may not be positive until 4-12 weeks post-infection) 1, 4
• Filarial testing only for West Africa exposure (day/night blood samples no longer recommended first-line) 1
• Complete blood count with differential to quantify eosinophil level 6

Treatment Algorithm

For Asymptomatic Eosinophilia in Travelers/Migrants

Empirical treatment for patients >24 months old: albendazole 400 mg single dose PLUS ivermectin 200 μg/kg single dose 1, 2, 4

This combination covers the most common helminth infections including:

• Hookworm (Ancylostoma, Necator) 2, 4
• Ascaris lumbricoides 4
• Strongyloides stercoralis 2, 4

For Specific Diagnosed Infections

• Strongyloidiasis: Ivermectin 200 μg/kg daily for 2 days 2
• Schistosomiasis: Praziquantel 40 mg/kg in two divided doses for 1 day 2
• Hookworm: Albendazole 400 mg single dose 2, 4
• Trichuriasis: Albendazole 400 mg single dose 1

For Eosinophilic Esophagitis

Initial approach: Proton pump inhibitor (PPI) twice daily for 8-12 weeks to identify PPI-responsive esophageal eosinophilia 1, 2

If PPI trial fails:

• Topical corticosteroids (swallowed fluticasone or budesonide) induce remission in 88% of patients 2, 5
• Two-food elimination diet (milk +/- wheat or egg) for 8-12 weeks with dietitian support 2, 5
• Diagnostic confirmation: Endoscopy with ≥6 biopsies from ≥2 sites showing ≥15 eosinophils/hpf 1, 5

For Hypereosinophilia with Organ Involvement

Any patient with evidence of end-organ damage (cardiac, pulmonary, neurologic) requires urgent medical assessment and emergency treatment consideration 1, 2

• Eosinophilic meningitis (Angiostrongylus): Corticosteroids (prednisolone 60 mg daily for 14 days) plus albendazole 15 mg/kg/day for 14 days 1, 2
• Neuroschistosomiasis: Praziquantel 40 mg/kg twice daily for 5 days plus dexamethasone 4 mg four times daily 2
• Toxocariasis with neurologic involvement: Corticosteroids plus albendazole 2

Monitoring and Follow-Up

Post-Treatment Assessment

• Repeat eosinophil counts after treatment to confirm response 2, 5
• For eosinophilic esophagitis: Histological remission defined as <15 eosinophils per 0.3 mm² on repeat endoscopy 2, 5
• Persistent elevation: If eosinophilia ≥1.5 × 10⁹/L persists >3 months despite treatment, refer to hematology 1, 2

Hematology Referral Indications

Refer to hematology when:

• Eosinophilia ≥1.5 × 10⁹/L for >3 months with no identified infectious cause 1, 2
• Evidence of end-organ damage (cardiac, pulmonary, neurologic) 1, 4
• Suspicion for primary/clonal eosinophilia 7, 3

Hematology workup includes:

• Bone marrow morphology and cytogenetics 7, 3
• FISH for PDGFRA, PDGFRB, FGFR1 rearrangements 7, 3
• Flow cytometry and T-cell clonality assessment 7, 3
• Next-generation sequencing for molecular markers 3

Critical Pitfalls to Avoid

• Do not rely on eosinophilia alone for helminth screening: Many helminth infections do not cause eosinophilia, particularly during chronic intestinal phase 1, 4
• Timing matters: Stool microscopy may be negative during tissue migration phase when eosinophilia is highest 4
• Serologic cross-reactivity: Helminth serologies may cross-react between species 4
• PPI trial essential: Always trial PPI before diagnosing eosinophilic esophagitis, as PPI-responsive esophageal eosinophilia is a distinct entity 1
• Peripheral eosinophils don't predict tissue eosinophilia: In eosinophilic esophagitis, peripheral counts may be normal despite significant tissue involvement 5
• Organ damage can occur at any level: Persistent eosinophilia of any degree can cause cardiac, pulmonary, and CNS damage 1, 4

Special Populations

Immunocompromised Patients

Strongyloides hyperinfection syndrome carries high mortality in immunosuppressed patients; aggressive screening and treatment is mandatory before initiating immunosuppression 1, 4

Patients with Refractory Disease

• Consider joint management with appropriate specialists (gastroenterology, allergy, rheumatology) 5
• Optimize treatment of underlying atopic conditions 5
• For idiopathic hypereosinophilic syndrome: Corticosteroids first-line, hydroxyurea or interferon-α for steroid-refractory cases 7, 3
• Mepolizumab (anti-IL-5 antibody) approved for idiopathic HES 3