Is eosinophilia common in pulmonary conditions such as pulmonary alveolar proteinosis, pneumocystis jirovecii pneumonia, or cryptogenic organizing pneumonia?

Eosinophilia in Pulmonary Conditions

Eosinophilia is not a common feature of pulmonary alveolar proteinosis or pneumocystis jirovecii pneumonia, but is frequently observed in cryptogenic organizing pneumonia and other eosinophilic lung diseases. 1, 2

Eosinophilia in Specific Pulmonary Conditions

Pulmonary Alveolar Proteinosis

• Eosinophilia is not a characteristic feature of pulmonary alveolar proteinosis
• The pathology typically involves accumulation of surfactant proteins in alveoli
• Diagnostic features include:
  • Ground-glass opacities with "crazy paving" pattern on CT
  • Milky appearance of bronchoalveolar lavage fluid
  • PAS-positive material in alveoli on histology

Pneumocystis Jirovecii Pneumonia (PJP)

• Eosinophilia is not typically associated with PJP 1
• PJP is characterized by:
  • Bilateral diffuse infiltrates on chest imaging
  • Ground-glass opacities
  • Diagnosis made by direct visualization/cytology of the organism
  • Occurs primarily in immunocompromised patients (HIV, transplant recipients, patients on immunosuppressive therapy)
• The European Crohn's and Colitis Organisation guidelines specifically note that PJP is not associated with eosinophilia 1

Cryptogenic Organizing Pneumonia (COP)

• Eosinophilia can be present in COP, though it's not universal 3, 4
• COP is characterized by:
  • Patchy consolidation with peripheral/subpleural predominance
  • Migratory infiltrates
  • Bronchiolitis obliterans with organizing pneumonia on histology
  • Rapid response to corticosteroids
• A 2023 study notes the clinical overlap between COP and idiopathic eosinophilic pneumonia, with both conditions potentially presenting with similar clinical and radiological findings 3

Pulmonary Conditions Commonly Associated with Eosinophilia

Eosinophilic Pneumonias

• Acute eosinophilic pneumonia

  • Rapid onset respiratory symptoms
  • Diffuse pulmonary infiltrates
  • BAL eosinophilia >25%
  • Peripheral blood eosinophilia may be absent initially

• Chronic eosinophilic pneumonia

  • Peripheral blood eosinophilia >1,000 cells/μL in 80-90% of cases 5
  • Classic "photographic negative of pulmonary edema" in about one-third of cases 4
  • Strong association with asthma (50% of patients) 4
  • Dramatic response to corticosteroids

Drug-Induced Pneumonitis

• Tissue eosinophilia, chronic interstitial inflammation, and lymphoid aggregates are common features of drug-related pneumonitis 1
• Multiple drugs can cause eosinophilic lung disease, including:
  • Antibiotics (nitrofurantoin, sulfonamides)
  • NSAIDs
  • Antiepileptics
  • Chemotherapeutic agents

Parasitic Infections

• Parasitic lung infections frequently cause eosinophilia 1, 2
• Examples include:
  • Loeffler's syndrome (transient pulmonary infiltrates with eosinophilia due to Ascaris, hookworm, or Strongyloides larvae migration)
  • Tropical pulmonary eosinophilia (hypersensitivity to filarial worms)
  • Paragonimiasis

Diagnostic Approach to Pulmonary Eosinophilia

• Defined as peripheral blood eosinophil count >500 cells/mm³ with pulmonary symptoms 6
• Supported by:
  • BAL eosinophilia (usually >10%)
  • Tissue eosinophilia on lung biopsy
• Diagnostic workup should include:
  • Complete blood count with differential
  • Chest imaging (radiograph and/or CT)
  • Consideration of bronchoscopy with BAL
  • Evaluation for parasitic infections in appropriate clinical context
  • Medication review

Clinical Implications

• Recognition of eosinophilia in pulmonary conditions helps guide diagnostic and therapeutic approaches
• Corticosteroids are the mainstay of treatment for most eosinophilic lung diseases
• Early diagnosis and treatment of eosinophilic pneumonias is essential to prevent progression to respiratory failure
• In drug-induced eosinophilic pneumonitis, withdrawal of the offending agent is crucial

Conclusion

When evaluating patients with pulmonary infiltrates and eosinophilia, cryptogenic organizing pneumonia should be considered in the differential diagnosis, while pulmonary alveolar proteinosis and pneumocystis jirovecii pneumonia are less likely causes. The presence of eosinophilia should prompt consideration of eosinophilic pneumonias, drug reactions, and parasitic infections as potential diagnoses.