What is the appropriate diagnosis and treatment approach for a pediatric patient presenting with thrombocytosis and eosinophilia?

Thrombocytosis with Eosinophilia in Pediatric Patients

In a pediatric patient presenting with both thrombocytosis and eosinophilia, the most likely diagnosis is secondary (reactive) thrombocytosis triggered by an underlying condition causing the eosinophilia—most commonly parasitic infection, allergic disease, or less frequently, a myeloproliferative disorder. 1, 2

Initial Diagnostic Approach

Immediate Assessment Priorities

• Obtain a detailed travel history focusing on fresh water exposure in Africa/tropical regions, raw/undercooked meat consumption, and timing relative to symptom onset, as helminth infections account for 19-80% of eosinophilia cases in returning travelers 3

• Assess for atopic conditions including allergic rhinitis, asthma, and atopic dermatitis, which are present in 50-80% of pediatric patients with eosinophilia 4, 5

• Evaluate for gastrointestinal symptoms such as dysphagia or food impaction that would warrant endoscopy for eosinophilic esophagitis 4, 3

• Document the degree of thrombocytosis: mild (500,000-700,000/μL), moderate (700,000-900,000/μL), severe (>900,000/μL), or extreme (>1,000/μL) 6

• Document the degree of eosinophilia: mild (0.5-1.5 × 10⁹/L), moderate-to-severe (≥1.5 × 10⁹/L) 3

Critical Red Flags Requiring Urgent Evaluation

Screen immediately for end-organ damage if eosinophilia is ≥1.5 × 10⁹/L or if any concerning symptoms are present 3, 7:

• Cardiac involvement: chest pain, dyspnea, heart failure symptoms, arrhythmias—obtain ECG, cardiac troponin, NT-proBNP, and echocardiography 3

• Pulmonary involvement: persistent cough, wheezing, infiltrates on imaging—perform chest X-ray and pulmonary function tests 3

• Neurological involvement: altered mental status, focal deficits, peripheral neuropathy—consider electromyography 3

• Bleeding manifestations: can occur despite elevated platelet counts due to acquired von Willebrand syndrome in the setting of extreme thrombocytosis 4

Diagnostic Workup Algorithm

First-Line Laboratory Studies

• Complete blood count with differential to confirm thrombocytosis and eosinophilia, and evaluate for other cytopenias or abnormalities 4, 2

• Peripheral blood smear examination looking for:

  • Normal platelet morphology (giant platelets approaching RBC size suggest primary disorder) 4
  • Atypical lymphocytes (can occur with eosinophilia in children) 4
  • Immature or abnormal cells (would suggest myeloproliferative disorder) 4

• Stool microscopy for ova and parasites (3 separate concentrated specimens) 8, 3

• Serology for Strongyloides and schistosomiasis if fresh water exposure in endemic areas 8, 3

• Serum ferritin to exclude iron deficiency as a cause of reactive thrombocytosis 1, 6

Second-Line Studies Based on Clinical Context

• Bone marrow aspiration is indicated if:

  • Atypical presenting features are present 4
  • Extreme thrombocytosis (>1,000/μL) persists without clear reactive cause 2, 6
  • Peripheral smear shows immature or abnormal cells 4
  • Eosinophilia ≥1.5 × 10⁹/L persists >3 months after excluding/treating infections 3

• Endoscopy with multiple biopsies if gastrointestinal symptoms present, as peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis (likely similar in children) 4, 3

• JAK2, CALR, MPL mutation testing if primary thrombocytosis suspected (extremely rare in children—incidence 1 per million) 6

Most Likely Diagnoses by Clinical Pattern

Pattern 1: Mild-Moderate Thrombocytosis + Mild Eosinophilia

Most likely: Reactive thrombocytosis secondary to:

• Parasitic infection (especially with travel history) 8, 3, 1
• Atopic disease (eczema, asthma, allergic rhinitis) 4, 5
• Acute or chronic infection 1, 6
• Iron deficiency 1, 6

Management approach:

• Treat underlying condition (empiric antiparasitic therapy if travel history: albendazole 400 mg single dose plus ivermectin 200 μg/kg single dose) 8
• No platelet-directed therapy needed 1, 6
• Avoid aspirin due to risk of Reye syndrome and platelet dysfunction 4
• Monitor platelet count until resolution 6

Pattern 2: Extreme Thrombocytosis (>1,000/μL) + Eosinophilia

Requires more aggressive evaluation for:

• Primary myeloproliferative disorder (essential thrombocythemia, chronic myeloid leukemia) 4, 2, 6
• Severe reactive process (malignancy, severe infection) 2, 6

Management approach:

• Immediate hematology consultation 1, 2, 6
• Bone marrow aspiration with cytogenetics 2
• Assess for bleeding risk (acquired von Willebrand syndrome can occur with extreme thrombocytosis) 4
• Consider cytoreduction if symptomatic or platelet count continues rising 4

Pattern 3: Moderate-Severe Eosinophilia (≥1.5 × 10⁹/L) + Thrombocytosis

Raises concern for:

• Hypereosinophilic syndrome (requires eosinophilia ≥1.5 × 10⁹/L with end-organ damage) 7, 5
• Eosinophilic granulomatosis with polyangiitis (usually >1,500 cells/μL or >10%) 9
• Parasitic infection with reactive thrombocytosis 8, 5

Management approach:

• Systematic evaluation for end-organ damage (cardiac, pulmonary, neurologic, GI, dermatologic) 3
• Complete parasitic workup regardless of eosinophil level if any travel history 3
• Hematology referral if eosinophilia ≥1.5 × 10⁹/L persists >3 months after infectious causes excluded/treated 3
• Corticosteroids are first-line for hypereosinophilic syndrome once diagnosed 8

Common Pitfalls to Avoid

• Do not assume normal eosinophil counts exclude parasitic infection—many helminth-infected patients have normal counts 8, 3

• Do not use aspirin for thrombocytosis prophylaxis in children due to Reye syndrome risk and platelet dysfunction 4

• Do not delay parasitic workup in children with travel history, even with mild eosinophilia, as Strongyloides can persist lifelong and cause fatal hyperinfection if immunosuppressed 3

• Do not rely solely on peripheral eosinophil counts to assess tissue eosinophilia in conditions like eosinophilic esophagitis—tissue biopsy is gold standard 4, 3

• Do not overlook atypical lymphocytes and eosinophilia on smear as these can occur in children with ITP and do not necessarily indicate malignancy 4

Monitoring and Follow-Up

• Repeat CBC in 2-4 weeks after treating underlying condition to confirm resolution 8, 6

• If thrombocytosis persists unexplained beyond 4-6 weeks, hematology consultation is warranted 1, 6

• If eosinophilia ≥1.5 × 10⁹/L persists >3 months after infectious causes excluded/treated, refer to hematology for hypereosinophilic syndrome evaluation 3, 7

• Close monitoring without treatment is appropriate for most cases of reactive thrombocytosis once underlying cause is addressed 1, 6