What are the common causes of eosinophilia in children?

Causes of Eosinophilia in Children

Primary Etiologic Categories

Allergic/atopic disorders account for approximately 80% of eosinophilia cases in children, followed by parasitic infections (particularly in endemic regions), primary immunodeficiencies, drug reactions, and less commonly malignancies and rheumatic diseases. 1, 2

Allergic and Atopic Conditions (Most Common)

• Food allergies, asthma, atopic dermatitis, and allergic rhinitis represent the dominant causes of mild to moderate eosinophilia in pediatric populations 1, 2
• Food allergy specifically emerges as an independent risk factor for childhood eosinophilia (OR: 1.866) 2
• Eosinophilic esophagitis presents with feeding difficulties in infants/toddlers, vomiting or pain in school-aged children, and dysphagia in adolescents, typically in atopic males (3:1 male predominance) 3
• Eosinophilic gastroenteritis accounts for 22.7% of hypereosinophilia cases in some pediatric series 4

Parasitic and Infectious Causes

In less affluent settings and endemic regions, parasitic infections become the second most common etiology, with specific geographic patterns determining the likely pathogen. 3

• Intestinal helminths including Ascaris lumbricoides, hookworm (Ancylostoma duodenale, Necator americanus), and Strongyloides stercoralis cause eosinophilia particularly in travelers and migrants from tropical areas 3, 1
• Toxocara infection was identified in 25% of children with chronic cough and eosinophilia in one Iranian study 3
• Schistosomiasis presents with Katayama syndrome (fever, urticarial rash, eosinophilia) 2-9 weeks after freshwater exposure in Africa 3, 5
• Acute bronchial pneumonia represents the most common infectious cause (11 of 28 infection-related cases in one series) 4
• Tuberculosis appears more commonly in less affluent settings 3

Primary Immunodeficiencies

Primary immunodeficiency disorders are significantly more common in children than adults with hypereosinophilia (5% vs 0.4%) and should be strongly considered in moderate to severe cases, especially in regions with high consanguinity rates. 6, 4, 2

• PIDs emerge as an independent risk factor for childhood eosinophilia (OR: 2.200) 2
• All three cases of immunodeficiency in one series presented with moderate to severe eosinophilia 4
• This etiology is particularly important in Middle Eastern and eastern Mediterranean countries where consanguineous marriages are common 2

Drug Reactions

• NSAIDs, beta-lactam antibiotics, and nitrofurantoin are the most commonly implicated medications 1, 7
• Medication timeline within the past 3 months should be documented 7, 5

Malignancies and Hematologic Disorders

• Hematologic neoplasms (including myeloid and lymphoid neoplasias with tyrosine kinase fusion genes) account for 2.3% of cases 1, 4
• Solid tumors, especially in advanced disease, can cause eosinophilia 1
• Importantly, most malignancy cases present with mild eosinophilia, not severe 2

Other Causes

• Rheumatic diseases including eosinophilic granulomatosis with polyangiitis (0.7-1.1% of cases) 4, 2
• ABO hemolysis (2.3%) 4
• Eosinophilic cystitis (1.1%) 4
• Idiopathic hypereosinophilic syndrome is rare in children (0.3%) 2

Age-Related Patterns

The etiology of eosinophilia varies significantly by age group, with younger children more likely to have infectious causes and older children more likely to have allergic conditions. 3

• Infants and toddlers with eosinophilic esophagitis present with feeding difficulties 3
• School-aged children present more commonly with vomiting or abdominal pain 3
• Adolescents demonstrate dysphagia as the predominant symptom in eosinophilic esophagitis 3

Severity-Based Distribution

Children with severe eosinophilia (≥5.0 × 10⁹/L) have higher peak eosinophil counts than adults and more commonly present with gastrointestinal complaints (62% vs 34%) and less pulmonary involvement (34% vs 59%). 6

• Mild eosinophilia (0.5-1.5 × 10⁹/L): predominantly allergic diseases (80.8% of all cases) 2
• Moderate eosinophilia (≥1.5 × 10⁹/L): allergic diseases and PIDs most common (17.8% of all cases) 2
• Severe eosinophilia (≥5.0 × 10⁹/L): PIDs most common etiology (1.4% of all cases) 2

Critical Clinical Pitfalls

Hypereosinophilia (≥1.5 × 10⁹/L) is never explained by allergy alone and always requires comprehensive workup to exclude secondary causes including parasites, drugs, PIDs, and myeloproliferative disorders. 7, 5

• Eosinophilia may be transient during tissue migration phase of parasitic infections when stool microscopy remains negative 3, 7
• Serological tests for helminths may not become positive until 4-12 weeks after infection 7
• Multiple etiologies may coexist in up to 28% of patients 3, 8
• Geographic context fundamentally alters the differential diagnosis, with pulmonary eosinophilia from parasites being relatively common in less affluent settings 3