What is the role of Immunoglobulin E (IgE) and eosinophil count in managing chronic cough post viral infection?

Role of IgE and Eosinophil Count in Managing Chronic Cough Post Viral Infection

Eosinophil count testing should be performed in patients with persistent cough following viral infections, as non-asthmatic eosinophilic bronchitis (NAEB) accounts for 10-30% of chronic cough cases and requires inhaled corticosteroid treatment. 1

Diagnostic Value of Eosinophil Count and IgE

Eosinophil Count

• Sputum eosinophilia (>3% non-squamous cells) is the key diagnostic marker for identifying eosinophilic airway inflammation 1
• Eosinophilic airway inflammation is present in 30-50% of chronic cough sufferers 2
• Induced sputum testing is the gold standard for detecting airway eosinophilia 1, 3
• In post-viral cough that persists beyond the typical 3-8 week period, studies show:
  • 33.6% of patients have sputum eosinophilia 4
  • 18.5% have NAEB (eosinophilia without bronchial hyperresponsiveness) 4
  • 14.3% have cough variant asthma (eosinophilia with bronchial hyperresponsiveness) 4

IgE Testing

• Elevated IgE levels may indicate atopic cough or allergic triggers 1
• IgE testing helps identify potential allergic components but is not diagnostic on its own 1
• While some patients with eosinophilic inflammation have elevated IgE, the correlation is not consistent enough for IgE to replace direct measurement of airway eosinophilia 5

Clinical Algorithm for Post-Viral Chronic Cough

1. For cough persisting 3-8 weeks after viral infection:

   • Consider induced sputum testing for eosinophil count 4
   • Perform spirometry and methacholine challenge test to assess for bronchial hyperresponsiveness 3

2. If sputum eosinophilia >3% is present:

   • Without bronchial hyperresponsiveness: Diagnose as NAEB 1
   • With bronchial hyperresponsiveness: Diagnose as cough variant asthma 4

3. If no sputum eosinophilia:

   • Consider other causes: post-infectious cough, upper airway cough syndrome, gastroesophageal reflux 1

Treatment Based on Eosinophil Count

For Eosinophilic Inflammation (NAEB or asthma):

• First-line treatment: Inhaled corticosteroids 1
  • Typical regimen: Budesonide 400 μg twice daily or equivalent 1
  • Treatment leads to significant reduction in sputum eosinophil count (from mean 16.8% to 1.6%) 6
  • Improvement in cough typically occurs within 2-4 weeks 1

For Non-eosinophilic Post-Viral Cough:

• Consider inhaled ipratropium bromide as it may attenuate post-infectious cough 1
• Antibiotics have no role in post-infectious cough management unless bacterial infection is confirmed 1
• For severe paroxysms of cough, a short course of oral prednisone (30-40mg daily) may be considered 1

Pitfalls and Caveats

1. Diagnostic challenges:

   • Sputum induction requires specialized equipment and expertise 1
   • Normal spirometry does not exclude eosinophilic bronchitis 1
   • If cough persists beyond 8 weeks, consider diagnoses other than post-infectious cough 1

2. Treatment considerations:

   • Failure to identify eosinophilic inflammation may lead to inappropriate treatment 6
   • Response to inhaled corticosteroids confirms the diagnosis of eosinophilic bronchitis 1
   • Duration of treatment is not well established; consider tapering once symptoms resolve 1

3. Follow-up:

   • Monitor sputum eosinophil counts to confirm treatment response 1
   • Consider occupational or environmental triggers if symptoms recur 1
   • Some patients may require long-term inhaled corticosteroid therapy 1

In summary, eosinophil count testing is essential in the management of chronic cough following viral infections, while IgE testing provides supplementary information about potential allergic components. Identifying eosinophilic inflammation guides appropriate treatment with inhaled corticosteroids, which significantly improves outcomes.