What is the appropriate initial approach to a patient presenting with peripheral eosinophilia?

Initial Approach to Peripheral Eosinophilia

Begin by obtaining a detailed travel and exposure history, calculating the absolute eosinophil count, and immediately ordering three concentrated stool specimens for ova and parasites plus Strongyloides serology, as helminth infections account for 19-80% of cases in travelers/migrants and can cause fatal hyperinfection syndrome even decades after exposure. 1, 2

Immediate Risk Stratification

Red Flags Requiring Urgent Evaluation

• Any patient with eosinophilia presenting with chest pain, dyspnea, heart failure symptoms, altered mental status, focal neurological deficits, or peripheral neuropathy requires immediate assessment for end-organ damage. 1
• Cardiac involvement is the leading cause of mortality in hypereosinophilic syndrome, occurring in 20% of cases. 3
• Pulmonary infiltrates with persistent cough or wheezing demand urgent evaluation to prevent irreversible fibrosis. 1

Severity Classification by Absolute Eosinophil Count

• Mild eosinophilia (0.5-1.5 × 10⁹/L): Most commonly allergic disorders or medications in non-endemic populations; helminth infections in travelers. 1, 2
• Moderate-to-severe eosinophilia (≥1.5 × 10⁹/L): Never explained by allergy alone and always requires comprehensive workup. 3
• Hypereosinophilia (≥1.5 × 10⁹/L persisting >3 months or >5.0 × 10⁹/L at any time): Carries significant risk of end-organ damage and mortality. 1

Essential History Elements

Geographic and Exposure Details

• Document exact travel locations, timing relative to symptom onset (eosinophilia typically appears 4-12 weeks post-exposure during tissue migration), freshwater swimming in Africa/tropical regions, walking barefoot, raw/undercooked meat or fish consumption, and water sources. 1, 3
• Migrants tend to have higher infection burden; travelers have more pronounced immune responses with marked eosinophilia. 2

Medication Timeline

• Review all medications added within the past 3 months, as drug-induced eosinophilia is a common non-infectious cause. 3

Atopic History

• Assess for asthma, eczema, and allergic rhinitis, which account for approximately 80% of eosinophilia in non-tropical populations. 2, 3

Symptom-Specific Inquiries

• Dysphagia or food impaction: Warrants endoscopy with multiple biopsies (minimum 6: 2-3 proximal, 2-3 distal esophagus) for eosinophilic esophagitis. 1
• Fever, weight loss, night sweats: Raise concern for malignancy or systemic vasculitis. 1
• Gastrointestinal symptoms: May indicate helminth infection or eosinophilic gastrointestinal disease. 1

First-Line Laboratory Workup

Mandatory Initial Tests

• Three separate concentrated stool specimens for ova and parasites on different days, regardless of symptoms. 2, 3
• Strongyloides serology for all patients given risk of fatal hyperinfection syndrome (70% mortality in immunocompromised), even >50 years after exposure. 2, 3
• Schistosomiasis serology if freshwater exposure in endemic areas (particularly Africa) within past 4-8 weeks. 3
• Complete blood count with differential to calculate absolute eosinophil count. 3

Additional Testing Based on Exposure

• Filariasis serology if travel to endemic regions with appropriate exposure history. 2
• Critical warning for Loa loa: If microfilariae seen on blood film, do NOT use diethylcarbamazine as it may cause fatal encephalopathy; use corticosteroids with albendazole first to reduce microfilarial load to <1000/ml. 1

Organ Damage Assessment (for Hypereosinophilia ≥1.5 × 10⁹/L)

Cardiac Evaluation

• Obtain electrocardiogram, cardiac troponin, and NT-proBNP in all patients with hypereosinophilia. 1
• Echocardiography when cardiac troponin elevated or clinical features suggest cardiac injury. 1
• Cardiac MRI indicated when elevated troponin or clinical cardiac features present. 1

Pulmonary Evaluation

• Chest X-ray to identify infiltrates (migratory infiltrates suggest Loeffler's syndrome; interstitial/reticulonodular patterns suggest tropical pulmonary eosinophilia). 1
• Pulmonary function tests if respiratory symptoms present. 1

Neurologic Evaluation

• Electromyography if sensory or motor deficits present to confirm eosinophil-induced peripheral neuropathy. 1

Treatment Approach

Empiric Antiparasitic Therapy

• For asymptomatic eosinophilia in patients >24 months with suspected helminthic infection: albendazole 400 mg single dose PLUS ivermectin 200 μg/kg single dose. 2
• For Strongyloidiasis: Ivermectin 200 μg/kg daily for 2 days. 1
• For Schistosomiasis: Praziquantel 40 mg/kg as single dose, repeated at 6-8 weeks; add prednisolone 20 mg/day for 5 days in acute Katayama syndrome. 1
• For tropical pulmonary eosinophilia: Diethylcarbamazine (after excluding Loa loa) plus adjunctive prednisolone 20 mg/day for 5 days; 20% relapse requiring re-treatment. 1

Eosinophilic Esophagitis Management

• First-line treatment is topical swallowed corticosteroids (fluticasone or budesonide), which decrease blood eosinophil counts in 88% of patients. 1
• Maintenance therapy mandatory after achieving remission due to high relapse rates. 1
• Endoscopic dilation safe for fibrostenotic disease but must combine with anti-inflammatory therapy. 1

Critical Pitfalls to Avoid

• Do NOT assume normal eosinophil counts exclude parasitic infection—many helminth-infected patients have normal counts. 1
• Do NOT rely solely on peripheral eosinophil counts for eosinophilic esophagitis—only 10-50% of adults have peripheral eosinophilia; tissue biopsy is gold standard. 1
• Do NOT wait for symptoms before investigating persistent moderate-to-severe eosinophilia—end-organ damage can be subclinical initially. 1
• Do NOT use diethylcarbamazine if Loa loa microfilariae present on blood film. 1
• Only tissue-invasive helminths cause eosinophilia, limiting its application as general screening tool. 4

Follow-Up and Referral

• Monitor eosinophil counts after treatment to confirm resolution. 2
• Refer to hematology if eosinophilia persists ≥1.5 × 10⁹/L for >3 months without identified cause after treatment or exclusion of infectious causes. 1, 2, 3
• For eosinophilic esophagitis, repeat endoscopy with biopsies if symptoms recur during treatment. 1