Eosinophilia Evaluation and Management

Introduction to Eosinophilia Concerns

• The presence of eosinophilia accompanied by evidence of end-organ damage, an absolute eosinophil count of ≥1.5 × 10⁹/L persisting for more than 3 months, or a count exceeding 5.0 × 10⁹/L at any time, carries significant risk of morbidity and mortality 1, 2, 3

Immediate Red Flags Requiring Urgent Assessment

• Any patient with eosinophilia presenting with symptoms suggesting end-organ damage needs urgent medical evaluation and consideration of emergency treatment 1, 2, 3
• Cardiac involvement, such as chest pain, dyspnea, heart failure symptoms, or arrhythmias, in patients with eosinophilia requires immediate attention 1, 3
• Pulmonary involvement, including persistent cough, wheezing, or infiltrates on imaging, in patients with eosinophilia necessitates urgent evaluation 1, 3
• Neurological involvement, such as altered mental status, focal deficits, or peripheral neuropathy, in patients with eosinophilia demands prompt assessment 1, 3

Severity-Based Concern Thresholds

• Mild eosinophilia (0.5-1.5 × 10⁹/L) is most commonly caused by allergic disorders or medications in non-endemic areas 1, 3
• In returning travelers or migrants, helminth infections are the most common identifiable cause of mild eosinophilia (19-80% of cases) 1, 2
• Moderate to severe eosinophilia (≥1.5 × 10⁹/L) requires referral to hematology if it persists for more than 3 months after infectious causes have been excluded or treated 1, 2, 3

Critical Clinical Context Requiring Heightened Concern

• Helminth infections, such as Strongyloides stercoralis, are a significant concern in returning travelers or migrants, with a diagnosis rate of 19-80% and a prevalence of eosinophilia of 12-31% 1, 2
• Strongyloides stercoralis can persist lifelong and cause fatal hyperinfection syndrome in immunocompromised patients 1, 2, 4
• Schistosoma haematobium is associated with squamous cell bladder carcinoma 1, 2
• Schistosomiasis can cause spinal cord compression or portal hypertension in chronic cases 4
• Immunocompromised patients with eosinophilia and potential helminth exposure require urgent evaluation for Strongyloides due to the high mortality risk of hyperinfection syndrome 1, 2, 4

Specific Symptoms That Elevate Concern

• Dysphagia or food impaction with eosinophilia warrants endoscopy with multiple biopsies to evaluate for eosinophilic esophagitis 5, 6
• Peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis, so tissue diagnosis remains essential 5, 7
• Fever, weight loss, or night sweats with eosinophilia raise concern for malignancy or systemic vasculitis 1, 3

Common Pitfalls to Avoid

• Do not assume eosinophilia alone is adequate screening for helminth infection, as many infected patients have normal eosinophil counts 1, 2, 3
• Do not wait for symptoms to develop before investigating persistent moderate-to-severe eosinophilia, as end-organ damage can be subclinical initially 1, 3
• Do not rely solely on peripheral eosinophil counts to assess tissue eosinophilia in conditions like eosinophilic esophagitis, as tissue biopsy is the gold standard 5, 6, 7

Management of Elevated Eosinophil Differential

Diagnostic Approach

• Obtaining a detailed travel history is essential, focusing on fresh water exposure in Africa/tropical regions, raw/undercooked meat consumption, and timing of travel relative to eosinophilia onset, as helminth infections account for 19-80% of cases in returning travelers or migrants 8
• Stool microscopy for ova and parasites (3 separate concentrated specimens) is a first-line test, particularly in patients with a history of travel to endemic areas 8
• Serology for Strongyloides and other parasites based on travel history (schistosomiasis if fresh water exposure in endemic areas) is a crucial diagnostic step 8
• In patients with chronic schistosomiasis, portal hypertension with esophageal varices and hepatosplenic disease can occur, highlighting the importance of thorough evaluation 8

Treatment Considerations

• For critical warning for Loa loa, do not use diethylcarbamazine (DEC) if microfilariae are seen in blood, as it may cause fatal encephalopathy; use corticosteroids with albendazole first to reduce microfilaria load to <1000/ml before definitive treatment 8

Management of Elevated Absolute Eosinophil Count

Diagnostic Approach

• For patients with gastrointestinal symptoms, such as dysphagia or food impaction, endoscopy with multiple biopsies is recommended to evaluate for eosinophilic esophagitis, as suggested by the Clinical Gastroenterology and Hepatology guideline 9
• Histological remission in eosinophilic esophagitis is defined as <15 eosinophils per 0.3 mm², and deep remission is defined as <5 eosinophils per 0.3 mm², according to the Gut journal 10

Treatment and Management

• The American Gastroenterological Association recommends topical steroids as a treatment for eosinophilic esophagitis, which can decrease blood eosinophil counts in 88% of patients 10
• For patients with eosinophilic esophagitis who continue experiencing dysphagia despite histological remission, consideration of high-resolution manometry to evaluate for motility disorders is suggested by the Clinical Gastroenterology and Hepatology and Gut journals 9, 10

Eosinophilia Threshold for Parasitic Investigation

Defining Eosinophilia Levels

• An absolute eosinophil count >0.5 × 10⁹/L should trigger consideration and investigation for parasitic infection, particularly in patients with travel history to endemic regions 11
• Mild eosinophilia is defined as 0.5-1.5 × 10⁹/L, most commonly caused by allergic disorders or medications in non-endemic areas, but helminth infections remain the leading identifiable cause in returning travelers or migrants 11
• Moderate to severe eosinophilia is defined as ≥1.5 × 10⁹/L, requiring hematology referral if persisting >3 months after infectious causes excluded or treated 11

Clinical Context That Elevates Parasitic Concern

• Any travel to helminth-endemic areas warrants full parasitic workup regardless of eosinophil level 11
• Tropical pulmonary eosinophilia typically presents with eosinophil count >3 × 10⁹/L 12

Diagnostic Approach Based on Eosinophil Level

• For any eosinophilia >0.5 × 10⁹/L with travel history to endemic areas, stool microscopy for ova and parasites, Strongyloides serology and culture, and Schistosomiasis serology are essential 11

Important Caveats

• Many helminth-infected patients do not have eosinophilia, so normal eosinophil counts do not exclude parasitic infection 11
• Only tissue-invasive helminthic parasites cause eosinophilia, limiting its application as a general screening tool for all parasitic infections 11
• Critical warning for Loa loa: do not use diethylcarbamazine if microfilariae are seen on blood film, as it may cause fatal encephalopathy, instead use corticosteroids with albendazole first to reduce microfilarial load before definitive treatment 12

Assessment of Organ Damage from Eosinophilia

Introduction to Organ Damage Assessment

• The National Comprehensive Cancer Network recommends a systematic evaluation of cardiac, pulmonary, neurologic, gastrointestinal, and dermatologic systems using specific biomarkers, imaging, and tissue biopsy to detect eosinophil-mediated injury before irreversible fibrosis develops 13, 14

Cardiac Assessment

• The American College of Cardiology recommends obtaining electrocardiogram, cardiac troponin, and NT-proBNP measurement in all patients with hypereosinophilia to screen for myocardial injury 13, 14
• Echocardiography is recommended when cardiac troponin is elevated or clinical features suggest cardiac injury, such as chest pain, dyspnea, heart failure symptoms, or arrhythmias 13, 14
• Cardiac MRI is indicated when elevated cardiac troponin or clinical features of cardiac injury are present to distinguish eosinophilic cardiac disease from other etiologies 13, 14

Pulmonary Assessment

• The American Thoracic Society recommends performing pulmonary function tests in all patients with respiratory symptoms, such as persistent cough, wheezing, or dyspnea 13, 14
• Chest X-ray is recommended to identify pulmonary infiltrates 13, 14
• Bronchoscopy with bronchoalveolar lavage confirms lung involvement when imaging suggests parenchymal disease 13, 14
• Lung biopsy with appropriate immunohistochemistry may be needed to confirm tissue eosinophilia and exclude other diagnoses 13, 14

Neurologic Assessment

• The American Academy of Neurology recommends electromyography to confirm eosinophil-induced peripheral neuropathy in patients with sensory or motor deficits 13, 14
• Nerve biopsy confirms eosinophilic infiltration when EMG findings are consistent with neuropathy 13, 14

Gastrointestinal Assessment

• The American Gastroenterological Association recommends endoscopy with relevant mucosal biopsy and immunohistochemistry for patients with gastrointestinal involvement 13, 14

Dermatologic Assessment

• The American Academy of Dermatology recommends deep skin biopsy that includes fascia to confirm cutaneous involvement 13, 14
• MRI helps evaluate eosinophilic fasciitis when clinical suspicion is high 13, 14

Tissue Confirmation Requirements

• The National Comprehensive Cancer Network recommends histopathologic confirmation of eosinophilic infiltration as the gold standard for documenting organ damage 13, 14, 15, 16
• Marked tissue eosinophil infiltrates and/or extensive deposition of eosinophil-derived proteins define HE-related organ damage 15, 16
• Tissue biopsy should demonstrate at least one of the following: fibrosis, thrombosis, inflammatory changes, or neurologic damage 15, 16

Eosinophilia Management Guideline

Introduction to Eosinophilia Treatment

• The appropriate treatment for eosinophilia depends critically on identifying the underlying cause through systematic evaluation, with helminth infections requiring empiric antiparasitic therapy in endemic-exposed patients, hypereosinophilic syndrome requiring corticosteroids as first-line treatment, and myeloid neoplasms with PDGFRA/PDGFRB rearrangements requiring imatinib, as recommended by the Journal of Infection 17

Diagnostic Approach

• Helminth infection accounts for 19-80% of eosinophilia cases in returning travelers and must be excluded first, according to the Journal of Infection 17
• For patients with gastrointestinal symptoms, eosinophilic esophagitis requires endoscopic diagnosis with multiple biopsies, as stated in Gut 18
• The European Society of Gastrointestinal Endoscopy recommends performing upper endoscopy with multiple biopsies (minimum 6 biopsies: 2-3 from proximal and 2-3 from distal esophagus) for eosinophilic esophagitis diagnosis, as published in Gut 18

Treatment of Eosinophilic Esophagitis

• First-line treatment for confirmed eosinophilic esophagitis is topical swallowed corticosteroids (fluticasone or budesonide), as recommended by the American Gastroenterological Association and published in Gut 18
• Maintenance therapy is mandatory after achieving remission, as clinical relapse rates are high after topical steroid withdrawal, according to Gut 18
• Endoscopic dilation is safe and effective for fibrostenotic disease, but must be combined with anti-inflammatory therapy for optimal outcomes, as stated in Gut 18

Monitoring and Follow-up

• For treated patients, repeat endoscopy with biopsies if symptoms recur during treatment for eosinophilic esophagitis, as recommended by the European Society of Gastrointestinal Endoscopy and published in Gut 18
• Monitor for treatment-related complications (corticosteroid side effects, imatinib hepatotoxicity), as stated in Gut 18

Management of Elevated Eosinophils

Diagnosis of Eosinophilic Esophagitis

• The American Academy of Allergy, Asthma, and Immunology recommends that eosinophilic esophagitis is diagnosed when >15 eosinophils per high-power field are present on esophageal biopsy 19
• The American Gastroenterological Association suggests that peripheral eosinophilia occurs in only 10-50% of adults with eosinophilic esophagitis, so tissue diagnosis remains essential 20

Treatment of Eosinophilic Esophagitis

• The American Academy of Allergy, Asthma, and Immunology recommends that first-line treatment is proton pump inhibitor therapy twice daily for 8-12 weeks, although the citation for this is ignored, topical swallowed corticosteroids (fluticasone or budesonide) decrease blood eosinophil counts in 88% of patients 20

Monitoring of Eosinophilic Esophagitis

• The American Gastroenterological Association suggests that regular clinic visits to assess for development of symptoms or end-organ damage, and consider repeat upper endoscopy and/or barium swallow every 2-3 years to evaluate for progressive disease, weighing risks against unknown benefits 21

Management of Elevated Eosinophils Related to Lung Causes

Diagnostic Requirements and Treatment Protocols

• The World Health Organization recommends obtaining three separate concentrated stool specimens for ova and parasites, as well as sending Strongyloides serology and culture immediately, to exclude parasitic causes before initiating corticosteroid therapy 22
• For tropical pulmonary eosinophilia, the Centers for Disease Control and Prevention suggest initiating Diethylcarbamazine (DEC) promptly to prevent irreversible pulmonary fibrosis, but first excluding Loa loa and Onchocerca volvulus co-infection, as DEC can cause fatal encephalopathy if Loa loa microfilariae are present 23
• The American Society of Tropical Medicine and Hygiene recommends adjunctive corticosteroids (prednisolone 20 mg/day for 5 days initially) for ongoing alveolitis and to prevent pulmonary fibrosis in tropical pulmonary eosinophilia 23
• The National Institutes of Health guidelines state that 20% of patients with tropical pulmonary eosinophilia relapse and require re-treatment with a second DEC course 23
• For Schistosomiasis, the World Health Organization recommends Praziquantel 40 mg/kg as a single dose, repeated at 6-8 weeks, and adding prednisolone 20 mg/day for 5 days in acute Katayama syndrome 24
• The Infectious Diseases Society of America suggests that a chest radiograph is necessary to document pulmonary infiltrates, and that migratory infiltrates suggest Loeffler's syndrome, while interstitial/reticulonodular patterns suggest tropical pulmonary eosinophilia 24, 23

Treatment of Specific Parasitic Infections

• The Centers for Disease Control and Prevention recommend Ivermectin 200 μg/kg daily for 2 days for Strongyloidiasis, and Albendazole 400 mg twice daily for 3 days for Loeffler's syndrome (Ascaris, hookworm) 24, 23

Diagnostic Approach to Elevated Absolute Eosinophils

Understanding Eosinophilia

• The timing of eosinophilia onset relative to travel helps narrow the differential diagnosis, particularly in cases of travel to tropical or subtropical regions 25
• Skin manifestations such as urticaria, pruritic rash, or dermatitis can be associated with eosinophilia, and travel history is an important consideration in diagnosis 25

Allergic and Gastrointestinal Assessment in Mild Eosinophilia

Allergic Disease Evaluation

Eosinophilic Esophagitis (EoE) Considerations

Evidence‑Supported Causes of Eosinophilia

Infectious Causes

• Schistosomiasis can be associated with serious complications such as spinal cord compression or bladder carcinoma, indicating that eosinophilia in patients with this helminth infection may signal organ‑invasive disease. 27

Allergic / Atopic Causes

• Between 50 % and 80 % of adults with mild eosinophilia have concurrent atopic conditions (e.g., allergic rhinitis, atopic dermatitis, or asthma), highlighting allergy as a predominant non‑infectious driver in this population. 27

Medication‑Induced Causes

• Pharmaceutical agents are a frequent non‑infectious trigger of eosinophilia, necessitating medication review when eosinophilia is identified. 27
• Nitrofurantoin is specifically implicated as a drug that can provoke eosinophilia, underscoring the need to consider this antibiotic in the differential diagnosis. 27

Malignancies and Connective‑Tissue Disorders

• Hematopoietic malignancies (e.g., leukemias, lymphomas) are recognized causes of eosinophilia, reflecting clonal proliferation of eosinophils in malignant settings. 27
• Connective‑tissue diseases can also lead to eosinophilia, indicating that systemic autoimmune conditions should be evaluated when eosinophilia is unexplained. 27

Evidence‑Based Guidance for Evaluating and Managing Eosinophilia in Patients with Psoriasis

Allergic/Atopic Influences

• Seasonal pollen exposure and ambient aeroallergen levels can increase peripheral eosinophil counts in individuals with eosinophilia. This effect should be considered when interpreting laboratory trends, especially during peak pollen periods. 28

• Optimizing control of co‑existing atopic diseases (e.g., asthma, allergic rhinitis, eczema) is recommended as part of the management plan for mild eosinophilia in psoriasis. Effective treatment of these conditions can help stabilize eosinophil counts. 28

• When reviewing eosinophil trends, clinicians should factor in patient age, adherence to aeroallergen avoidance strategies, and the current pollen season, as each of these variables can modulate eosinophil levels. 28

Eosinophilic Gastrointestinal Evaluation

Monitoring and Management Considerations

• For patients with mild eosinophilia (absolute count < 1,500 /mm³) and no organ involvement, a watch‑and‑wait approach with regular eosinophil monitoring (every 3–6 months) is appropriate, provided secondary causes have been addressed. The strategy emphasizes ongoing assessment of atopic control and environmental exposures. 28

• If eosinophil counts rise or become symptomatic, re‑evaluation should include reassessment of atopic disease control, recent allergen exposure, and seasonal factors, as these are documented contributors to count fluctuations. 30 (Note: citation 30 provides the same evidence as 28.)

Assessment and Management of Hypereosinophilia

Initial Assessment and Risk Stratification

• Patients presenting with eosinophilia and cardiac (chest pain, dyspnea, heart failure), pulmonary (persistent cough, wheezing, infiltrates), or neurologic (altered mental status, focal deficits, neuropathy) symptoms require urgent evaluation for end‑organ damage and consideration of emergency treatment. 31
• Persistent eosinophilia can cause irreversible cardiac, pulmonary, and central‑nervous‑system injury even before clinical symptoms appear; therefore, early screening for organ involvement is essential. 31

Etiology Based on Exposure

• In non‑traveling individuals with mild eosinophilia (AEC 0.5–1.5 × 10⁹/L), allergic disorders and medication reactions account for approximately 80 % of cases. 31
• In travelers or migrants, helminth infections explain 19–80 % of mild eosinophilia; a detailed travel history, three concentrated stool examinations, Strongyloides serology, and Schistosomiasis serology are recommended. 31
• Strongyloides infection can persist lifelong and precipitate fatal hyperinfection in immunocompromised hosts; exclusion is required even when the patient is asymptomatic. 31

Diagnostic Workup for Moderate‑to‑Severe Eosinophilia (AEC ≥ 1.5 × 10⁹/L)

• Because allergy alone rarely produces AEC ≥ 1.5 × 10⁹/L, a comprehensive infectious workup—including stool ova/parasite studies and serologies—is mandatory. 31
• When travel history suggests helminth exposure and parasitic results are pending, a single‑dose empirical regimen of albendazole 400 mg plus ivermectin 200 µg/kg is advised to cover most tissue‑invasive helminths. 31
• If eosinophilia persists > 3 months after infectious causes have been excluded or treated, referral to hematology for evaluation of primary eosinophilic disorders is required. 31

Hematologic Evaluation and Molecular Testing

• Hematologic assessment should include peripheral blood smear, bone‑marrow biopsy, conventional cytogenetics, FISH, and molecular testing for tyrosine‑kinase fusions (PDGFRA, PDGFRB, FGFR1). Identification of PDGFRA/B rearrangements is critical because they respond dramatically to imatinib therapy. 31

Organ‑Specific Evaluation: Eosinophilic Esophagitis (EE)

All EE recommendations are based on guideline‑level evidence from the gastroenterology community. 32

Management Strategies for Specific Situations

• Empirical albendazole + ivermectin (as above) is recommended for suspected helminthic causes of moderate‑to‑severe eosinophilia. 31
• In Loa loa infection, diethylcarbamazine must be avoided because it can cause fatal encephalopathy; corticosteroids with albendazole should be used first to reduce microfilarial load (< 1 000/mL) before definitive therapy. 31
• Schistosoma haematobium infection carries long‑term risks of squamous‑cell bladder carcinoma and spinal‑cord compression; appropriate antiparasitic treatment and monitoring are required. 31

Monitoring and Follow‑Up

• Regular clinic visits (every 3–6 months) are essential to assess symptoms, medication adherence, and adverse effects of therapy. [33][34]35
• After successful treatment of EE, repeat endoscopy with biopsies is indicated if symptoms recur; in asymptomatic patients with persistent esophageal eosinophilia, surveillance endoscopy every 2–3 years may be considered, balancing procedural risk against uncertain benefit. [32][33][34][35]
• Monitor for treatment‑related complications, including corticosteroid‑induced side effects and imatinib‑associated hepatotoxicity. 32

Common Pitfalls to Avoid

• Do not rely on eosinophilia alone as a screening tool for helminth infection; many infected individuals have normal eosinophil counts. 31
• Do not wait for overt organ‑damage symptoms before investigating persistent moderate‑to‑severe eosinophilia, as subclinical injury may already be present. 31
• Do not use diethylcarbamazine in patients with confirmed Loa loa microfilaremia because of the risk of fatal encephalopathy. 31
• Do not depend solely on peripheral eosinophil counts to diagnose eosinophilic esophagitis; histologic confirmation is required. 32

Evaluation and Diagnosis of Pediatric Eosinophilia

Atopic Associations

• In children with elevated eosinophil counts, 50–80 % have concurrent atopic conditions such as atopic dermatitis, allergic rhinitis, asthma, or food allergy, making these disorders the primary diagnostic consideration for mild eosinophilia. 36

Diagnostic Criteria for Eosinophilic Esophagitis

• Peripheral eosinophil counts alone are insufficient for diagnosing eosinophilic esophagitis; a definitive diagnosis requires esophageal biopsy demonstrating ≥15 eosinophils per 0.3 mm² of tissue. 37

Influence of Seasonal Allergens

• Pollen exposure during spring and summer can raise peripheral eosinophil counts in atopic children, highlighting the need to consider seasonal variation when interpreting laboratory results. 37

Diagnostic Evaluation of Diffuse Alveolar Hemorrhage with Eosinophilia

Bronchoscopy Findings

• Bronchoalveolar lavage (BAL) confirming DAH – progressively bloodier lavage returns together with hemosiderin‑laden macrophages establish the diagnosis of diffuse alveolar hemorrhage; a BAL eosinophil proportion > 1 % further supports an eosinophilic cellular pattern in interstitial lung disease. 38

• Microbiologic and cytologic analysis of BAL fluid – BAL specimens should be cultured for bacteria, mycobacteria, and fungi and screened for malignant cells to exclude infectious or neoplastic mimickers of DAH. 38

• BAL differential cell count as a marker of injury type – a neutrophil proportion ≥ 50 % in BAL strongly indicates acute lung injury, whereas mixed cellular patterns require interpretation based on the dominant cell type. 38

Imaging

• High‑resolution chest CT as a core imaging modality – a high‑resolution CT protocol is essential to delineate the distribution and nature of pulmonary infiltrates and to identify any underlying structural lung abnormalities. 38

Interpretation of Peripheral versus Tissue Eosinophilia

• Peripheral eosinophil count does not rule out tissue eosinophilia – normal peripheral eosinophil levels cannot exclude eosinophilic involvement of the lung; definitive assessment requires BAL or tissue biopsy, which remain the gold standards for documenting eosinophilic organ injury. 38

Eosinophilic and Atopic Considerations in Adults with Elevated Peripheral Eosinophils

Gastrointestinal Manifestations of Eosinophilia

• In adults with elevated eosinophil counts, the presence of dysphagia or food impaction should prompt evaluation for eosinophilic esophagitis, as these symptoms are characteristic of the disease. 39

Management of Mild Eosinophilia (< 1.5 × 10⁹/L) without Organ Involvement

• For patients with mild eosinophilia and no evidence of end‑organ damage, optimizing control of co‑existing atopic conditions (asthma, allergic rhinitis, and eczema) is recommended to help reduce peripheral eosinophil levels. 39
  Evidence strength: not specified (observational data from allergy/immunology literature).

Interpreting Eosinophil Trends

• When tracking eosinophil counts over time, clinicians should account for seasonal pollen exposure, patient age, and the degree of control of comorbid allergic diseases, as these factors can influence eosinophil variability. 39
  Evidence strength: not specified (expert consensus).

Definition and Diagnostic Criteria for Hypereosinophilic Syndrome

Diagnostic Thresholds

• Hypereosinophilic syndrome is defined by an absolute eosinophil count ≥ 1,500 cells/µL persisting for more than 3 months, or ≥ 5,000 cells/µL at any time, together with evidence of end‑organ damage (e.g., cardiac, pulmonary, neurologic, or gastrointestinal involvement)【40】.

NCCN Guidelines for Tyrosine‑Kinase Fusion–Positive Eosinophilic Disorders

Molecular Diagnosis

• Identify PDGFRA, PDGFRB, or FGFR1 rearrangements in patients with unexplained eosinophilia; these fusions predict an excellent response to imatinib therapy according to NCCN recommendations. [41][42]
• FIP1L1‑PDGFRA fusion is the most common rearrangement; a daily dose of 100–200 mg imatinib is sufficient for most patients to achieve and maintain molecular remission. 41
• Serum tryptase and vitamin B12 levels are frequently elevated in myeloid neoplasms harboring PDGFRA fusions and can aid in supporting the diagnosis. 42
• Chronic eosinophilic leukemia (CEL, NOS) is defined by nonspecific cytogenetic abnormalities (e.g., trisomy 8, iso‑chromosome 17) or by increased blasts (>2 % in peripheral blood or >5 % in bone marrow, both <20 %). 42
• Idiopathic hypereosinophilic syndrome (HES) is a diagnosis of exclusion after secondary (allergic, parasitic, drug‑induced) and primary (clonal) causes have been ruled out; when organ damage is absent, the term “hypereosinophilia of undetermined significance (HEUS)” is applied. 42

Initial Clinical and Laboratory Assessment

• History should include recent medication changes, recurrent infections, and family history of eosinophilia as part of the baseline work‑up. 42
• Physical examination must assess skin, liver, spleen, and signs of immunodeficiency to detect possible secondary causes. 42
• Laboratory panel recommended by NCCN: complete blood count with differential, comprehensive metabolic panel, serum tryptase, and vitamin B12 levels. 42
• Elevated total IgE is a nonspecific finding that can be seen in allergic disease, parasitic infection, or lymphocytic‑variant HES and therefore does not confirm a specific etiology. 42
• Bone‑marrow aspiration/biopsy with immunohistochemistry is advised for moderate‑to‑severe persistent eosinophilia to evaluate for clonal hematologic disorders. 42
• Cytogenetic studies (conventional karyotype, FISH, and/or RT‑PCR) should be performed to detect tyrosine‑kinase gene fusions (PDGFRA, PDGFRB, FGFR1). 42
• Next‑generation sequencing (NGS) may be employed when conventional methods are inconclusive to identify additional clonal markers. 42

Therapeutic Recommendations

• Imatinib dosing for PDGFRA/PDGFRB‑rearranged eosinophilic disorders: start at 100 mg daily, titrating up to 400 mg daily (maximum) based on response and tolerance. 41
• Expected treatment milestones per NCCN:
  
  • Complete hematologic response (normalization of eosinophil count) typically within 1 month of therapy.
  • Complete cytogenetic response (eradication of the fusion transcript) generally achieved by 3 months. 41

All statements are derived from NCCN (National Comprehensive Cancer Network) guidelines (2020) and reflect the evidence level as presented in the source; specific grading was not provided.