From the Guidelines
Eosinophilia is most commonly caused by allergic reactions, parasitic infections, or hematologic malignancies, and a thorough diagnostic workup is essential to determine the underlying cause and guide treatment. The causes of eosinophilia can be broadly categorized into primary (clonal) and secondary (reactive) eosinophilia [ 1 ]. Secondary eosinophilia is often associated with allergic disorders, parasitic infections, immunodeficiency syndromes, and solid tumors or lymphoid malignancies. Allergic conditions, such as asthma, atopic dermatitis, and allergic rhinitis, are the most common cause of secondary eosinophilia, occurring in about 80% of cases [ 1 ]. Parasitic infections, particularly those involving tissue-invasive helminths like Strongyloides, Ascaris, and Toxocara, are also significant causes of eosinophilia, especially in endemic regions or after travel [ 1 ].
Some key points to consider in the diagnosis and management of eosinophilia include:
- A thorough history and physical examination to identify potential causes of eosinophilia
- Targeted laboratory testing, such as complete blood counts, blood smears, and stool tests for parasites
- Consideration of referral to a hematologist or infectious disease specialist for further evaluation and management
- Treatment directed at the underlying cause of eosinophilia, rather than the eosinophilia itself
- Monitoring for potential end-organ damage, particularly in cases of persistent or severe eosinophilia [ 1 ].
In terms of specific causes, helminth infections are a common identifiable cause of eosinophilia in returning travelers and migrants, with diagnosis rates varying from 19% to 80% [ 1 ]. Strongyloides stercoralis infection, in particular, can persist lifelong and later present as hyperinfection syndrome, with a high mortality, in those who become immunocompromised [ 1 ]. Therefore, it is essential to consider helminth infections in the differential diagnosis of eosinophilia, particularly in individuals with a history of travel to endemic regions.
From the Research
Causes of Eosinophilia
- Eosinophilia can be caused by various factors, including parasitic diseases, allergic diseases, autoimmune diseases, connective tissue diseases, rheumatologic diseases, primary eosinophilia, and malignant states 2
- Hypereosinophilia, defined as a peripheral blood eosinophil count greater than 1.5 × 109 /L, can be associated with tissue damage and may be caused by primary or secondary eosinophilic disorders 3, 4
- Secondary causes of eosinophilia include parasitic infections, such as helminthic parasites, which can cause eosinophilia due to tissue invasion 5, 6
- Other non-hematologic (secondary or reactive) and hematologic (primary or clonal) disorders can also cause eosinophilia, including myeloid/lymphoid neoplasms with eosinophilia and rearrangement of PDGFRA, PDGFRB, or FGFR1 or with PCM1-JAK2 3, 4
Types of Eosinophilia
- Primary eosinophilia, such as hypereosinophilic syndrome (HES), is a diagnosis of exclusion and can be caused by an aberrant T-cell clone-driven reactive eosinophilia 3, 4
- Lymphocyte-variant hypereosinophilia is an aberrant T-cell clone-driven reactive eosinophilia 3, 4
- Idiopathic hypereosinophilic syndrome (HES) is a diagnosis of exclusion and can be caused by various factors, including primary or secondary eosinophilic disorders 3, 4
Diagnosis and Evaluation
- Diagnostic evaluation of primary eosinophilias relies on a combination of various tests, including morphologic review of the blood and marrow, standard cytogenetics, fluorescence in situ hybridization, next generation sequencing gene assays, and flow immunophenotyping 3, 4
- Disease prognosis relies on identifying the subtype of eosinophilia, and the 2016 World Health Organization endorses a semi-molecular classification scheme of disease subtypes 3, 4