What is the initial workup and treatment for a patient presenting with eosinophilia?

Workup for Eosinophilia

The initial workup for eosinophilia should include a comprehensive history (focusing on travel, new medications, recurrent infections, and family history of eosinophilia), physical examination, CBC with differential, comprehensive metabolic panel with uric acid, lactate dehydrogenase, liver function tests, serum tryptase levels, and vitamin B12 levels. 1

Initial Laboratory Evaluation

• Complete blood count with differential to confirm eosinophilia
• Peripheral blood smear to evaluate blood cell morphology and other abnormalities
• Comprehensive metabolic panel with uric acid, lactate dehydrogenase, and liver function tests
• Serum tryptase levels (elevated in myeloproliferative variants and systemic mastocytosis)
• Vitamin B12 levels (commonly elevated in myeloid neoplasms with PDGFRA fusion gene)
• Peripheral blood smear review for evidence of other blood count abnormalities 1, 2

Additional Testing Based on Clinical Presentation

For Suspected Parasitic Infection

• Concentrated stool microscopy (at least 3 specimens on different days)
• Strongyloides serology (high yield across all regions)
• Stool PCR for parasites (higher sensitivity than microscopy)
• Schistosomiasis serology (especially with freshwater exposure history)
• HIV testing for unexplained eosinophilia 2

For Suspected Allergic Disorders

• Serum immunoglobulin levels (including IgE)
• Aspergillus IgE to evaluate for allergic bronchopulmonary aspergillosis
• Erythrocyte sedimentation rate and/or C-reactive protein 1

For Suspected Autoimmune Disorders

• Antineutrophil cytoplasmic antibodies
• Antinuclear antibodies 1

Imaging Studies

• Chest X-ray to assess for pulmonary infiltrates
• Abdominal ultrasound to evaluate for hepatosplenomegaly 2

Advanced Diagnostic Procedures

Bone Marrow Evaluation

For persistent unexplained eosinophilia or suspected hematologic malignancy:

• Bone marrow aspirate and biopsy with immunohistochemistry for CD117, CD25, tryptase, and reticulin/collagen stains for fibrosis
• Conventional cytogenetics
• Fluorescence in situ hybridization (FISH) and/or nested reverse transcription PCR to detect TK fusion gene rearrangements 1

Classification of Eosinophilia

• Mild: 500-1500 cells/μL
• Moderate: 1500-5000 cells/μL
• Severe: >5000 cells/μL 3

Diagnostic Algorithm

1. Rule out secondary causes:

   • Parasitic infections (particularly in returning travelers)
   • Medication reactions
   • Allergic disorders
   • Autoimmune conditions

2. If secondary causes excluded, evaluate for primary eosinophilic disorders:

   • Myeloid/lymphoid neoplasms with eosinophilia and TK fusion genes
   • Chronic eosinophilic leukemia, not otherwise specified (CEL, NOS)
   • Lymphocyte-variant hypereosinophilia
   • Idiopathic hypereosinophilic syndrome (diagnosis of exclusion) 4

Initial Treatment Approach

Treatment depends on the underlying cause:

For Parasitic Infections

• Strongyloidiasis: Ivermectin 200 μg/kg/day for 1-2 days
• Toxocariasis (VLM): Albendazole 400mg twice daily for 5 days
• Schistosomiasis: Praziquantel 40 mg/kg twice daily for 5 days 2

For Primary Eosinophilic Disorders

• PDGFRA or PDGFRB rearrangements: Imatinib (exquisitely responsive)
• Lymphocyte-variant hypereosinophilia and HES: Corticosteroids as first-line therapy
• Steroid-refractory HES: Hydroxyurea or interferon-alpha 4

For Eosinophilic Enteritis

• Oral corticosteroids: Prednisolone 0.5-1 mg/kg/day for 2-4 weeks
• Dietary elimination approach for patients preferring non-pharmacological options 2

Common Pitfalls and Caveats

1. Failure to exclude secondary causes before diagnosing primary eosinophilic disorders
2. Missing parasitic infections in travelers or migrants from endemic areas
3. Overlooking medication-induced eosinophilia
4. Inadequate monitoring for end-organ damage in persistent eosinophilia
5. Delayed bone marrow evaluation in cases of unexplained persistent eosinophilia 5

Monitoring and Follow-up

• Regular monitoring of eosinophil counts every 1-3 months
• Assessment for resolution of symptoms
• Vigilance for end-organ damage, particularly cardiac complications
• Repeat endoscopy with biopsy if symptoms recur while on treatment 2

For patients with mild eosinophilia (<1500/mm³) without symptoms or signs of organ involvement, a watch-and-wait approach with close follow-up may be appropriate 4.