What are the causes of chronic eosinophilia?

Causes of Chronic Eosinophilia

The main causes of chronic eosinophilia include helminth infections (particularly in travelers and migrants), allergic/atopic disorders, drug reactions, autoimmune diseases, hematological malignancies, and hypereosinophilic syndromes. 1

Infectious Causes

Helminth Infections

• Helminths are the most common identifiable cause of eosinophilia in returning travelers and migrants, with diagnosis rates varying from 19%-80% 2
• Common helminth infections causing eosinophilia include:
  • Strongyloides stercoralis - can persist lifelong and cause hyperinfection syndrome in immunocompromised patients 2
  • Schistosomiasis - particularly in those with history of freshwater exposure in Africa 1
  • Filariasis - especially in those with travel history to West Africa 1
  • Hookworm (Ancylostoma duodenale, Necator americanus) 1
  • Ascaris lumbricoides 1
  • Onchocerciasis (Onchocerca volvulus) - associated with river exposure in Africa, parts of Central/South America, and Arabian peninsula 2
  • Toxocariasis (T. canis, T. catis) - can cause visceral larva migrans 2

Fungal Infections

• Coccidioidomycosis and paracoccidioidomycosis can cause eosinophilia, especially in immunocompromised patients 2
• Eosinophilia is more common in coccidioidomycosis and juvenile paracoccidioidomycosis 2

Non-Infectious Causes

Allergic/Atopic Disorders

• Constitute approximately 80% of cases of secondary reactive eosinophilia 1
• Include asthma, food allergies, atopic dermatitis 1

Drug Reactions

• Common medications causing eosinophilia include:
  • Non-steroidal anti-inflammatory drugs 1
  • Beta-lactam antibiotics 1
  • Nitrofurantoin 1

Hematological Disorders

• Myeloid and lymphoid neoplasms with eosinophilia 1, 3
• Chronic eosinophilic leukemia, not otherwise specified (CEL, NOS) 3
• Myeloid/lymphoid neoplasms with rearrangement of PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2 3
• Lymphocyte-variant hypereosinophilia (aberrant T-cell clone-driven) 3

Other Causes

• Autoimmune and connective tissue disorders 4
• Solid tumors, especially in advanced disease 1
• Vasculitis, particularly eosinophilic granulomatosis with polyangiitis 4
• Idiopathic hypereosinophilic syndrome - diagnosis of exclusion after ruling out other causes 3

Clinical Significance and Complications

• Persistent eosinophilia, especially at high levels (>1.5 × 10⁹/L), can cause significant end-organ damage 2, 1
• Target organs commonly affected include:
  • Heart (myocarditis, endomyocardial fibrosis) 1
  • Lungs (pulmonary infiltrates) 1
  • Central nervous system (meningitis, encephalitis) 1
  • Skin (rashes, urticaria) 2
• Specific complications of chronic infections include:
  • Schistosomiasis: bladder carcinoma (S. haematobium), portal hypertension 2
  • Strongyloidiasis: hyperinfection syndrome with high mortality in immunocompromised patients 2
  • Onchocerciasis: dermatitis, keratitis, anterior uveitis, choroidoretinitis 2

Diagnostic Approach

• Detailed travel history is essential - geographic area visited helps narrow down potential helminth infections 2
• Consider timing of exposure - eosinophilia may be transient during tissue migration phase of infection 2
• Serological tests for helminths may not become positive until 4-12 weeks after infection 2
• For persistent eosinophilia ≥1.5 × 10⁹/L for more than 3 months with no identified cause, referral to hematology is recommended 2

Pitfalls to Avoid

• Many people with helminth infection do not have eosinophilia, so testing for eosinophilia alone is not an adequate screening strategy 2
• Serological tests may exhibit cross-reactivity between different helminth species 1
• Stool microscopy may be negative during the tissue migration phase of infection when eosinophilia is present 2
• Patients with eosinophilia and evidence of end-organ damage need urgent medical assessment 2