What is the appropriate treatment for elevated eosinophil (Eos) counts?

Management of Elevated Eosinophil Count

The appropriate treatment for elevated eosinophils depends entirely on identifying and treating the underlying cause through a systematic diagnostic workup, with parasitic infections, allergic conditions, and eosinophilic gastrointestinal disorders being the most common etiologies requiring specific interventions. 1

Initial Diagnostic Evaluation

Before initiating any treatment, you must systematically evaluate for the underlying cause:

Assess Severity and Duration

• Mild eosinophilia (500-1500 cells/μL): Most commonly due to allergic disorders including asthma, allergic rhinitis, and atopic dermatitis 2
• Moderate eosinophilia (1500-5000 cells/μL): Consider eosinophilic esophagitis and other tissue eosinophilic disorders 2
• Persistent eosinophilia ≥1.5 × 10⁹/L for >3 months: Requires hematology referral to exclude clonal disorders 1

Key Historical and Clinical Features to Elicit

• Travel history: Parasitic infections are common causes, particularly helminth infections 1, 3
• Gastrointestinal symptoms (dysphagia, food impaction): Suggests eosinophilic esophagitis requiring endoscopy 1, 3
• Atopic history: Assess for allergic rhinitis, asthma, and atopic dermatitis 1, 3
• Respiratory symptoms: Chronic cough alone causes eosinophilia in up to 40% of cases 2

Essential Diagnostic Testing

• Stool microscopy and serology for parasitic infections based on exposure history 1, 3
• Endoscopy with multiple biopsies (six biopsies from at least two different sites) if gastrointestinal symptoms present 3
• Evaluation for aeroallergen sensitivity given high rates (50-80%) of allergic diatheses 3

Treatment Based on Etiology

For Parasitic Infections

Empiric treatment is appropriate for returning travelers with asymptomatic eosinophilia:

• Albendazole 400 mg single dose PLUS ivermectin 200 μg/kg single dose 1, 3

For specific identified parasites:

• Strongyloidiasis: Ivermectin 200 μg/kg daily for 1-2 days 1
• Schistosomiasis: Praziquantel 40 mg/kg in two divided doses for 1 day 1
• Most other helminth infections: Albendazole 400 mg single dose 1, 3

For Eosinophilic Esophagitis

The diagnosis requires tissue biopsy showing >15 eosinophils per 0.3 mm² (or >15 eos/HPF) in esophageal tissue 4, 3

First-line treatment options:

• Proton pump inhibitor therapy twice daily for 8-12 weeks 1
• Topical steroids (fluticasone or budesonide) decrease blood eosinophil counts in 88% of patients 3, 2
• Two-food elimination diet (milk +/- wheat or egg) for 8-12 weeks with dietitian support 1, 3

Important caveat: Allergy testing to foods is NOT recommended for choosing dietary restriction therapy 1, 3

For Allergic Conditions

• Optimize treatment for underlying atopic disease (asthma, allergic rhinitis, atopic dermatitis) 3
• Corticosteroids are highly effective, with eosinophil counts decreasing 2- to 7-fold, with effects visible as early as 6 hours 2
• Management strategies targeting eosinophil normalization reduce severe asthma exacerbations by up to 60% 2

For Hypereosinophilic Syndrome and Idiopathic Eosinophilia

Corticosteroids are first-line therapy for hypereosinophilic syndrome 1, 5

For clonal eosinophilia with PDGFRA/PDGFRB rearrangements:

• Imatinib shows exquisite responsiveness and should be initiated immediately upon identification 6, 5

For steroid-refractory cases:

• Hydroxyurea and interferon-alfa have demonstrated efficacy 6, 5
• Anti-IL-5 antibodies (mepolizumab) or anti-IL-5 receptor antibodies (benralizumab) are under investigation 6

For Mild Asymptomatic Eosinophilia (<1.5 × 10⁹/L)

• Watch and wait approach with close follow-up is appropriate if no symptoms or signs of organ involvement 6

Monitoring Treatment Response

• Follow-up eosinophil counts after treatment to assess response 1, 3
• For eosinophilic esophagitis: Histological remission is <15 eosinophils per 0.3 mm², with deep remission being <5 eosinophils per 0.3 mm² 3
• If symptoms recur during treatment: Repeat endoscopy for assessment and histology 3
• For persistent eosinophilia despite treatment: Refer to hematology for further investigation 1

Critical Pitfalls to Avoid

• Peripheral blood eosinophil counts may not correlate with tissue eosinophilia, particularly in eosinophilic esophagitis where tissue biopsy remains the gold standard 3, 2
• Many people with helminth infection do not have eosinophilia, so testing for eosinophilia alone is inadequate screening 1
• Persistent eosinophilia of any degree can cause significant end-organ damage, particularly affecting the heart, lungs, and central nervous system 1
• Do not delay hematology referral for persistent eosinophilia ≥1.5 × 10⁹/L for >3 months, as clonal disorders require molecular testing for PDGFRA/PDGFRB rearrangements 1, 6