What is the approach to managing a patient with eosinophilia?

Approach to Eosinophilia

Begin by determining the absolute eosinophil count (AEC) and obtaining a detailed travel history focusing on freshwater exposure in Africa/tropical regions, raw/undercooked meat consumption, and timing relative to symptom onset, as helminth infections account for 19-80% of cases in returning travelers and migrants. 1, 2

Initial Risk Stratification

Immediately assess for end-organ damage by evaluating for chest pain, dyspnea, heart failure symptoms, altered mental status, focal neurological deficits, or persistent respiratory symptoms, as these require urgent evaluation and carry significant mortality risk. 2, 3

Severity Classification by AEC:

• Mild eosinophilia: 0.5-1.5 × 10⁹/L 2
• Moderate eosinophilia: 1.5-5.0 × 10⁹/L 4
• Severe eosinophilia: >5.0 × 10⁹/L 4

Note that values >20,000 cells/μL are highly suggestive of myeloproliferative disorders rather than allergic or parasitic causes. 4

Diagnostic Evaluation Algorithm

Step 1: Detailed History (Essential Elements)

Obtain specific exposure details: 1

• Exact timing and location of freshwater swimming (especially Africa)
• Consumption of raw/undercooked fish, meat, or salads
• Walking barefoot in endemic areas
• New medications started within the timeframe
• Household contacts with similar symptoms

Identify symptom patterns by system: 1

• Respiratory: wheeze, dry cough (suggests Loeffler's syndrome from Ascaris, hookworm, or Strongyloides)
• Gastrointestinal: diarrhea, abdominal pain, dysphagia (consider eosinophilic esophagitis or intestinal helminths)
• Neurological: severe headache, meningism (suggests Angiostrongylus or neurocysticercosis)
• Cutaneous: urticarial rash, migratory serpiginous lesions (cutaneous larva migrans)

Step 2: Timing Considerations

Understand that eosinophilia may be transient during the tissue migration phase (prepatent period) when parasite eggs/larvae are not yet detectable in stool, and eosinophilia often resolves when organisms reach the gut lumen. 1 This explains why stool microscopy may be negative despite active infection.

Step 3: Laboratory Investigations

For all patients with eosinophilia and travel/migration history, order: 1

• Concentrated stool microscopy (minimum 3 samples on separate days)
• Schistosoma serology (if freshwater exposure in endemic areas)
• Strongyloides serology (critical to exclude before corticosteroid use)
• Filarial serology (if appropriate geographic exposure)

Critical pitfall: Cross-reactivity is common in helminth serology (e.g., low-level positive filarial serology in strongyloidiasis), so only request tests where epidemiology supports the diagnosis to avoid false positives. 1

For gastrointestinal symptoms (dysphagia, abdominal pain): 2

• Perform upper endoscopy with minimum 6 biopsies from at least 2 different esophageal sites to evaluate for eosinophilic esophagitis
• Note that peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis

Treatment Approach

Asymptomatic Mild Eosinophilia in Returning Travelers

Administer empiric treatment with albendazole 400 mg single dose PLUS ivermectin 200 μg/kg single dose to cover possible prepatent or undetected geohelminth infections (ascariasis/hookworm/strongyloidiasis) when stool microscopy is negative. 1, 2, 3

CRITICAL: Exclude Loa loa infection in people who traveled to endemic regions (Central/West Africa) BEFORE treating with ivermectin to prevent severe adverse reactions. 1, 3

For suspected schistosomiasis: Repeat praziquantel treatment at 8 weeks, as eggs and immature schistosomulae are relatively resistant to initial treatment. 1

Confirmed Strongyloidiasis

Treat with ivermectin 200 μg/kg daily for 2 days. 2, 3 In immunocompromised patients, use ivermectin 200 μg/kg on days 1,2,15, and 16, with prolonged treatment for hyperinfection syndrome requiring specialist consultation. 1

Eosinophilic Esophagitis

First-line treatment is topical swallowed corticosteroids (fluticasone or budesonide), which decrease blood eosinophil counts in 88% of patients. 2 Maintenance therapy is mandatory after achieving remission due to high clinical relapse rates. 2

Acute Schistosomiasis (Katayama Syndrome)

Treat with praziquantel 40 mg/kg as single dose, repeated at 6-8 weeks, PLUS prednisolone 20 mg/day for 5 days for acute presentations with fever, rash, and marked eosinophilia 2-8 weeks after freshwater exposure. 1, 3

Tropical Pulmonary Eosinophilia

Initiate diethylcarbamazine (DEC) promptly to prevent irreversible pulmonary fibrosis, but FIRST exclude Loa loa co-infection. 3

Common Pitfalls to Avoid

Do not assume eosinophilia alone is adequate screening for helminth infection, as many infected patients have normal eosinophil counts. 3 Conversely, do not wait for symptoms to develop before investigating persistent moderate-to-severe eosinophilia, as end-organ damage can be subclinical initially and progress to irreversible fibrosis. 3

Never administer corticosteroids before excluding Strongyloides infection, as this can precipitate fatal hyperinfection syndrome. 1

Beware requesting serological tests where epidemiology does not support the diagnosis, as false positives from cross-reactivity are common. 1

Follow-Up Monitoring

Repeat eosinophil counts after treatment to assess response. 2, 3 For patients on corticosteroids, monitor for bone mineral density loss and adrenal suppression, particularly in children and adolescents. 2, 3

If symptoms recur while on treatment for eosinophilic esophagitis, repeat endoscopy with biopsies. 2 For asymptomatic patients with persistent eosinophilia after empiric treatment, consider repeat evaluation every 2-3 years to assess for progressive disease, though the optimal surveillance strategy remains uncertain. 1