What is the initial approach to treating eosinophilic leucocytosis?

Initial Approach to Eosinophilic Leucocytosis

The initial approach to eosinophilic leucocytosis must prioritize identifying and treating life-threatening causes—particularly parasitic infections in travelers and end-organ damage—before pursuing extensive hematologic workup. 1, 2

Immediate Risk Assessment

Any patient with evidence of end-organ damage requires urgent medical assessment and consideration of emergency treatment regardless of the absolute eosinophil count. 2 The most critical complications include:

• Cardiac involvement (Löeffler endocarditis): This is the primary cause of mortality in hypereosinophilic syndromes, presenting with myocardial fibrosis, systemic thromboembolism, and acute heart failure 2
• Eosinophilic meningitis or encephalitis: Requires immediate corticosteroids plus albendazole 1
• Severe respiratory involvement: Including Loeffler's syndrome with pulmonary infiltrates 3

Initial Diagnostic Workup

History and Physical Examination

Focus on specific high-yield elements 3, 1:

• Travel history: Particularly fresh water exposure in Africa (schistosomiasis), tropical regions (strongyloidiasis, hookworm)
• New medications: Drug-induced eosinophilia
• Recurrent infections: Suggesting immunodeficiency syndromes
• Skin evaluation: Urticaria, rash patterns
• Hepatosplenomegaly: Palpation for organomegaly
• Cardiac and neurological examination: For end-organ involvement

Laboratory Testing

All patients with eosinophilia returning from the tropics should be investigated with concentrated stool microscopy. 3 The initial panel should include 3, 1:

• CBC with differential: Define degree of eosinophilia
• Comprehensive metabolic panel: Including liver function tests, uric acid, lactate dehydrogenase
• Serum tryptase and vitamin B12 levels: Elevated in myeloproliferative variants, particularly PDGFRA fusion genes 3
• Serology for parasites: Strongyloides, Schistosoma, and other helminths based on travel history 3, 1
• Stool ova and parasites: Three separate specimens 1
• IgE levels: Nonspecific but elevated in allergies, infections, and lymphocyte-variant hypereosinophilia 3

Treatment Algorithm Based on Clinical Context

For Asymptomatic Eosinophilia in Travelers (Age >24 months)

Empirical treatment is recommended when investigations are negative: Albendazole 400 mg single dose plus ivermectin 200 μg/kg single dose 1, 2

For Specific Parasitic Infections Identified

• Strongyloidiasis: Ivermectin 200 μg/kg daily for 2 days 1
• Schistosomiasis (Katayama syndrome): Praziquantel 40 mg/kg as a single dose, repeated at 6-8 weeks; add prednisone 20 mg/day for 5 days to reduce symptom duration 3
• Neuroschistosomiasis: Praziquantel 40 mg/kg twice daily for 5 days plus dexamethasone 4 mg four times daily 1
• Toxocariasis with neurological involvement: Corticosteroids plus albendazole 1

For Persistent Hypereosinophilia (≥1.5 × 10⁹/L)

If eosinophilia ≥1.5 × 10⁹/L persists for more than 3 months after excluding or treating infectious causes, refer to hematology for evaluation of primary eosinophilic disorders. 2, 4 This workup requires 3, 4:

• Bone marrow aspirate and biopsy: With immunohistochemistry for CD117, CD25, tryptase
• Conventional cytogenetics and FISH: To detect tyrosine kinase fusion genes (PDGFRA, PDGFRB, FGFR1)
• Molecular testing: Next-generation sequencing for clonal markers 4, 5
• Flow immunophenotyping: To detect aberrant T-cell clones 4

For Primary Eosinophilic Disorders

Identification of rearranged PDGFRA or PDGFRB is critical because of the exquisite responsiveness of these diseases to imatinib. 4, 5 Treatment hierarchy:

• Myeloid/lymphoid neoplasms with tyrosine kinase fusions: Imatinib is first-line 4, 5
• FGFR1-rearranged neoplasms: Pemigatinib recently approved for relapsed/refractory disease 4
• Lymphocyte-variant hypereosinophilia and idiopathic HES: Corticosteroids are first-line therapy 4, 5
• Steroid-refractory HES: Hydroxyurea or interferon-α 4, 5
• Idiopathic HES: Mepolizumab (IL-5 antagonist) is FDA-approved 5

Watch-and-Wait Approach

For patients with milder eosinophilia (<1.5 × 10⁹/L) without symptoms or signs of organ involvement, close follow-up without immediate treatment is appropriate. 4, 5 However, serial monitoring for end-organ damage is essential.

Critical Pitfalls to Avoid

• Do not delay treatment in patients with end-organ damage: This is a medical emergency requiring prompt aggressive therapy 2
• Do not rely on eosinophilia alone to screen for helminth infection: Many infected patients do not have eosinophilia 2
• Do not miss Strongyloides stercoralis: This can persist lifelong and cause fatal hyperinfection syndrome in immunocompromised patients 2
• Do not overlook cardiac involvement: Perform echocardiography or cardiac MRI if any cardiac symptoms are present, as this determines prognosis 2
• Do not assume asymptomatic means benign: Persistent eosinophilia of any degree can cause significant end-organ damage, particularly affecting the heart, lungs, and central nervous system 1

Follow-Up Monitoring

Obtain follow-up eosinophil counts after treatment to assess response. 1 For patients with identified end-organ damage, serial cardiac imaging is recommended if cardiac involvement was present. 2