What are the causes of eosinophilia (elevated eosinophil count)?

From the Guidelines

Eosinophilia is most commonly caused by allergic disorders, such as asthma, hay fever, and atopic dermatitis, which account for approximately 80% of cases, as well as parasitic infections, particularly those involving tissue-invasive helminths like Strongyloides, Ascaris, and hookworms. The causes of eosinophilia can be broadly categorized into several groups, including:

• Allergic disorders, such as allergic asthma, food allergy, atopic dermatitis, and drug reactions, which are the most common cause of secondary (reactive) eosinophilia, occurring in about 80% of cases 1
• Parasitic infections, particularly those involving tissue-invasive helminths like Strongyloides, Ascaris, and hookworms, which are significant causes, especially in endemic regions or travelers 1
• Autoimmune and inflammatory conditions, such as eosinophilic granulomatosis with polyangiitis (formerly Churg-Strauss syndrome), inflammatory bowel disease, and certain connective tissue disorders, which may present with eosinophilia 1
• Hematologic malignancies, including certain leukemias, lymphomas, and mastocytosis, which can cause eosinophilia through abnormal cytokine production 1
• Immunodeficiency syndromes, such as hyperimmunoglobulin E syndrome, Omenn syndrome, and Wiskott-Aldrich syndrome, which can be associated with abnormal immunoglobulin levels and eosinophilia 1
• Pulmonary conditions, such as eosinophilic pneumonia and certain skin diseases, which may also present with elevated eosinophil counts 1

It is essential to accurately diagnose the underlying cause of eosinophilia, taking into account histopathologic, clinical, laboratory, cytogenetic, and molecular criteria, to establish the appropriate treatment plan 1. If patients have eosinophilia ≥ 1.5 × 10⁹/L for more than 3 months but no evidence of end-organ damage, consider referring them to a hematologist for further investigations once infectious causes have been excluded or treated 1.

From the Research

Causes of Eosinophilia

• Eosinophilia can be caused by various factors, including:
  • Parasitic diseases 2, 3, 4
  • Allergic diseases 2, 5, 3
  • Autoimmune diseases 2, 5
  • Connective tissue diseases 2
  • Rheumatologic diseases 2
  • Primary eosinophilia, such as hypereosinophilic syndrome 2, 5
  • Malignant states 2
• Eosinophilia can also be associated with infectious diseases, including:
  • Allergic fungal rhinosinusitis 3
  • Mycetoma 3
  • Invasive fungal rhinosinusitis 3
  • Rhinosporidiosis 3
  • Baylisascariasis 3
  • Toxocariasis 3
  • Onchocerciasis 3
  • Loiasis 3
  • Histoplasmosis 3

Diagnostic Approach

• The diagnostic approach to eosinophilia should consider the type of patient, including previous travel and exposure history, comorbidities, and symptoms 4
• A multidisciplinary approach may be necessary to diagnose and manage eosinophilia, especially in severe cases with multiorgan involvement 5 Note: The study 6 is not relevant to the topic of eosinophilia.