What causes an increase in eosinophils (Eosinophilia)?

From the Guidelines

Eosinophilia is most commonly caused by allergic disorders, parasitic infections, and certain immunodeficiency syndromes, with allergic disorders accounting for approximately 80% of cases. According to the most recent and highest quality study 1, the underlying causes of eosinophilia can be broadly categorized into nonneoplastic and neoplastic conditions. Nonneoplastic conditions include allergic disorders, parasitic infections, autoimmune or inflammatory disorders, and immunodeficiency syndromes. Allergic disorders, such as allergic asthma, food allergy, atopic dermatitis, and drug reactions, are the most common cause of secondary (reactive) eosinophilia. Parasitic infections, particularly those caused by Strongyloides stercoralis, are the second most common cause.

Causes of Eosinophilia

• Allergic disorders: allergic asthma, food allergy, atopic dermatitis, drug reactions
• Parasitic infections: Strongyloides stercoralis, hookworms, roundworms
• Immunodeficiency syndromes: hyperimmunoglobulin E syndrome, Omenn syndrome, Wiskott Aldrich syndrome
• Autoimmune disorders: eosinophilic granulomatosis with polyangiitis, hypereosinophilic syndrome
• Certain cancers: leukemias, lymphomas

The study 1 emphasizes the importance of accurate diagnosis of the underlying cause of eosinophilia to establish the appropriate treatment plan. It also highlights the need to rule out secondary (reactive) eosinophilia caused by nonneoplastic or neoplastic conditions. Another study 1 notes that helminth infections are a common cause of eosinophilia in returning travelers and migrants, and that concentrated stool microscopy and strongyloides serology should be performed on all patients regardless of geographic exposure. However, since the study 1 is more recent and of higher quality, its findings take precedence. Therefore, it is essential to consider allergic disorders, parasitic infections, and immunodeficiency syndromes as the primary causes of eosinophilia, and to investigate and manage these conditions accordingly.

From the Research

Causes of Eosinophilia

Eosinophilia can be caused by a variety of factors, including:

• Allergic disorders, such as atopic dermatitis 2, 3
• Parasitic infections, such as helminthic parasites 2, 3, 4
• Leukemia/Lymphomas and solid tumors 2
• Vasculitis-Immunodeficiency diseases 2
• Autoimmune and connective tissue diseases 5
• Rheumatologic diseases 5
• Primary eosinophilia, such as hypereosinophilic syndrome 5, 3
• Malignant states 5
• Skin diseases, such as eosinophilic cellulitis, granuloma faciale, and eosinophilic fasciitis 6

Classification of Eosinophilia

Eosinophilia can be classified into different levels of severity, including:

• Mild eosinophilia: 500-1500 cells/μl 2
• Moderate eosinophilia: 1500-5000 cells/μl 2
• Severe eosinophilia: > 5000 cells/μl 2
• Hypereosinophilia: > 1500 cells/μl in at least two consecutive tests made with a minimum of a 4-week interval 2, 3

Clinical Manifestations

Eosinophilia can present with various clinical manifestations, including:

• Organ involvement, such as cardiac, pulmonary, and cutaneous damage 2
• Skin lesions, such as flame figures and eosinophilic infiltration 6
• Systemic symptoms, such as fever and malaise 3