Causes of Eosinopenia
Eosinopenia (defined as peripheral blood eosinophil count <0.5 × 10⁹/L) is most commonly caused by acute stress responses, infections, and corticosteroid administration.
Primary Causes of Eosinopenia
1. Acute Stress Responses
- Acute bacterial or viral infections 1
- Acute myocardial infarction 2
- Intracerebral hemorrhage 3
- Trauma or surgery
- Severe inflammatory states
2. Medication-Induced
- Corticosteroids - most common medication cause 4, 5
- Mechanism: Inhibit eosinophil adherence and chemotaxis
- Effect is dose-dependent and reversible
- Typically occurs within 4 hours of administration
- Adherence returns to normal within 24-48 hours 4
- Other immunosuppressive medications
3. Specific Infections
- COVID-19 - can cause eosinopenia even in patients with pre-existing eosinophilia 6
- Acute bacterial infections
- Overwhelming sepsis
4. Other Causes
- Cushing's syndrome (endogenous corticosteroid excess)
- Acute allergic reactions (initial phase)
- Critical illness
- Post-surgical states
Pathophysiological Mechanisms
Corticosteroid-induced eosinopenia occurs through:
- Reduced eosinophil adherence to vascular endothelium
- Inhibition of eosinophil chemotaxis
- Sequestration of eosinophils in lymphoid tissue
- These effects are non-toxic, cell-directed, and reversible 4
Infection-related eosinopenia occurs through:
- Acute inflammatory cytokine release
- Margination and tissue migration of eosinophils
- Suppression of eosinophil release from bone marrow
Clinical Significance
- Eosinopenia in acute myocardial infarction correlates with larger infarct size and worse clinical outcomes 2
- In intracerebral hemorrhage, eosinopenia is associated with higher mortality rates, especially when accompanied by neutrophilia 3
- In COVID-19, eosinopenia may mask underlying chronic eosinophilia from conditions like strongyloidiasis 6
- Idiopathic eosinopenia (without other blood count abnormalities) is extremely rare - a study of 24,300 hospitalized patients found only 24 cases, with 20 of those receiving corticosteroids 7
Important Considerations
- When evaluating eosinopenia, consider recent corticosteroid administration (even a single dose can cause transient eosinopenia)
- In patients with acute infections and eosinopenia, monitor for clinical deterioration as it may indicate severe disease
- In patients with previously documented eosinophilia who develop eosinopenia, consider acute infection or stress response
- For patients requiring immunosuppressive therapy who have traveled to endemic areas, screen for strongyloidiasis before treatment to prevent hyperinfection syndrome 6, 1
Monitoring and Follow-up
- For medication-induced eosinopenia, levels typically normalize after discontinuation of the causative agent
- In stress-induced eosinopenia, resolution of the underlying condition usually leads to normalization of eosinophil counts
- Regular monitoring of blood counts is recommended to confirm resolution 1
Remember that while eosinopenia itself rarely requires specific treatment, it may serve as an important marker of disease severity or response to therapy.