What is the appropriate diagnosis and treatment for a patient with back pain and elevated eosinophils (high eosinophil count)?

Back Pain and High Eosinophils: Diagnostic Approach and Management

Immediate Assessment for Life-Threatening Causes

In a patient presenting with back pain and elevated eosinophils, you must immediately evaluate for hypereosinophilic syndrome with cardiac or neurological involvement, as these conditions carry significant mortality risk and require urgent treatment. 1

Red Flag Symptoms Requiring Emergency Evaluation

• Cardiac symptoms (chest pain, dyspnea, heart failure, arrhythmias) suggest endomyocardial involvement, which is particularly associated with neoplastic hypereosinophilic syndromes and can be fatal 2, 1
• Neurological deficits (altered mental status, focal weakness, peripheral neuropathy) indicate potential CNS or spinal cord involvement requiring immediate imaging and treatment 1
• Spinal cord compression can occur with chronic schistosomiasis and presents as back pain with neurological symptoms 2, 1

Systematic Diagnostic Approach Based on Eosinophil Level

Mild Eosinophilia (0.5-1.5 × 10⁹/L)

• Most commonly caused by allergic disorders or medications in non-endemic areas 1
• In patients with travel history to tropical regions, helminth infections account for 19-80% of cases 1
• Back pain with mild eosinophilia suggests possible musculoskeletal causes coinciding with allergic or parasitic conditions 2

Moderate to Severe Eosinophilia (≥1.5 × 10⁹/L)

• Requires urgent hematology referral if persisting >3 months after infectious causes excluded 1, 3
• Absolute eosinophil count ≥1.5 × 10⁹/L carries significant risk of end-organ damage affecting heart, lungs, and nervous system 1, 3
• Any count >5.0 × 10⁹/L at any time requires immediate evaluation regardless of duration 1

Essential Diagnostic Workup

Travel and Exposure History

For any patient with eosinophilia, obtain detailed travel history focusing on:

• Fresh water exposure in Africa (schistosomiasis causing Katayama syndrome or chronic spinal involvement) 2, 1
• Tropical regions where Strongyloides stercoralis is endemic, as this parasite can persist lifelong and cause fatal hyperinfection in immunocompromised patients 2, 1
• Raw or undercooked meat consumption (trichinellosis causing severe myalgia and back pain) 2

Initial Laboratory Investigations

• Concentrated stool microscopy (minimum 3 samples) for helminth ova and parasites 2
• Serology for schistosomiasis and strongyloidiasis if travel history positive 2, 1
• Peripheral blood smear to assess eosinophil morphology and exclude myeloid neoplasms 3, 4
• Serum tryptase and vitamin B12 if myeloid neoplasm suspected (elevated in PDGFRA fusion-positive cases) 2, 5

Imaging and Specialized Testing

• Cardiac evaluation (ECG, echocardiogram, troponin) for any patient with eosinophilia ≥1.5 × 10⁹/L to detect endomyocardial involvement 2, 1
• Spinal MRI if back pain accompanied by neurological symptoms or signs of cord compression 2, 1
• Chest radiograph to evaluate for pulmonary infiltrates (Loeffler's syndrome, eosinophilic pneumonia) 2, 1

Hematologic Evaluation When Indicated

• Bone marrow biopsy with cytogenetics and molecular testing for PDGFRA, PDGFRB, FGFR1, and JAK2 rearrangements if primary eosinophilia suspected 2, 3, 4
• Flow cytometry and T-cell clonality assessment to exclude lymphocyte-variant hypereosinophilia 3, 4

Treatment Algorithm

For Parasitic Infections (Most Common in Travelers)

Empiric treatment is recommended for returning travelers with eosinophilia when initial testing is negative:

• Albendazole 400 mg single dose PLUS ivermectin 200 μg/kg single dose covers most helminth infections 2, 6
• For confirmed strongyloidiasis: Ivermectin 200 μg/kg daily for 1-2 days 6
• For schistosomiasis (Katayama syndrome): Praziquantel 40 mg/kg single dose, repeated at 6-8 weeks, plus prednisone 20 mg daily for 5 days to reduce symptom duration 2, 6
• For trichinellosis with severe myalgia/back pain: Albendazole 400 mg daily for 8-14 days in severe disease 2

For Primary Hypereosinophilic Syndrome

• Imatinib is first-line for PDGFRA or PDGFRB rearrangements due to exquisite responsiveness 3, 4
• Corticosteroids are first-line for idiopathic HES and lymphocyte-variant HE 6, 3, 4
• Mepolizumab (anti-IL-5 antibody) is FDA-approved for idiopathic HES refractory to other treatments 3, 4

Monitoring and Follow-Up

• Repeat eosinophil counts 2-4 weeks after antiparasitic treatment to assess response 6
• Serial cardiac monitoring for patients with eosinophilia ≥1.5 × 10⁹/L even if asymptomatic initially 1, 3
• Hematology referral mandatory if eosinophilia persists >3 months despite treatment of secondary causes 1, 3

Critical Pitfalls to Avoid

• Do not assume normal eosinophil count excludes helminth infection – many infected patients have normal counts, so testing based on exposure history is essential 1, 6
• Do not delay cardiac evaluation in patients with moderate-to-severe eosinophilia, as endomyocardial damage can be subclinical initially 2, 1
• Do not miss Strongyloides in immunocompromised patients – screen all patients with relevant exposure before starting immunosuppression due to fatal hyperinfection risk 2, 1
• Do not attribute all eosinophilia to allergies without excluding parasitic and hematologic causes, especially with persistent elevation 1, 7

Specific Context: Back Pain Considerations

When back pain is the primary symptom with eosinophilia, consider:

• Trichinellosis if severe myalgia accompanies back pain with recent raw meat consumption 2
• Chronic schistosomiasis causing spinal cord compression if travel to endemic areas 2, 1
• Hypereosinophilic syndrome with neurological involvement if back pain accompanied by weakness or sensory changes 1
• Coincidental musculoskeletal pain with unrelated eosinophilia from allergic or parasitic causes 2, 1