What are the causes of chronic eosinophilia (Eosinophilia, a condition characterized by an elevated eosinophil count)?

From the Guidelines

Chronic eosinophilia is most commonly caused by allergic disorders, parasitic infections, and medication reactions, and a thorough evaluation including history, complete blood count, and stool examination for parasites is essential for diagnosis and management. The causes of chronic eosinophilia can be categorized into several groups, including allergic disorders such as asthma, atopic dermatitis, and allergic rhinitis, which trigger eosinophil production through IgE-mediated hypersensitivity reactions 1. Parasitic infections, particularly helminth infections like strongyloidiasis, ascariasis, and schistosomiasis, represent another significant cause, especially in individuals with travel history to endemic regions 1. Medication reactions can also induce eosinophilia, with common culprits including antibiotics, NSAIDs, anticonvulsants, and allopurinol 1.

Some key points to consider in the evaluation and management of chronic eosinophilia include:

• Allergic disorders are the most common cause of secondary (reactive) eosinophilia, occurring in about 80% of cases 1
• Parasitic infections, particularly helminth infections, are a significant cause of eosinophilia in individuals with travel history to endemic regions 1
• Medication reactions can induce eosinophilia, and a thorough medication history is essential in the evaluation of chronic eosinophilia 1
• Hematologic malignancies, autoimmune and inflammatory conditions, and hypereosinophilic syndrome are also potential causes of chronic eosinophilia, and a comprehensive evaluation including complete blood count, stool examination for parasites, and potentially bone marrow examination or genetic testing is necessary for diagnosis and management 1

In terms of management, it is essential to identify and treat the underlying cause of eosinophilia, and to monitor for signs of end-organ damage. If patients have eosinophilia ≥ 1.5 × 10⁹/L for more than 3 months but no evidence of end-organ damage, consideration should be given to referring them to a hematologist for further investigations once infectious causes have been excluded or treated 1. Additionally, any patient presenting with evidence of end-organ damage needs urgent medical assessment and consideration of emergency treatment 1.

From the Research

Causes of Chronic Eosinophilia

• Eosinophilia can be caused by various factors, including:
  • Parasitic diseases 2, 3
  • Allergic diseases 4, 3
  • Autoimmune diseases 4
  • Connective tissue diseases 4
  • Rheumatologic diseases 4
  • Primary eosinophilia, such as hypereosinophilic syndrome 5, 6
  • Malignant states 4, 5
• Chronic eosinophilia can be classified into different subtypes, including:
  • Myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1 5
  • Chronic eosinophilic leukemia, not otherwise specified (CEL, NOS) 5, 6
  • Lymphocyte-variant hypereosinophilic syndrome (L-HES) 5, 6
  • Idiopathic hypereosinophilic syndrome (HES) 5, 6
• The diagnosis of chronic eosinophilia involves:
  • Exclusion of secondary causes of eosinophilia 5, 6
  • Morphologic review of the blood and marrow 5
  • Standard cytogenetics, fluorescence in situ hybridization, next generation sequencing gene assays, and flow immunophenotyping 5
• The treatment of chronic eosinophilia depends on the subtype and severity of the disease, and may include:
  • Corticosteroids 5, 6
  • Hydroxyurea 5, 6
  • Interferon-α 5, 6
  • Mepolizumab, an interleukin-5 (IL-5) antagonist monoclonal antibody 5, 6
  • Imatinib mesylate 5, 6