Eosinophilic Pneumonias

Description

• Eosinophilic pneumonias (pulmonary eosinophilia) represent a heterogenous group of diseases with a similar clinical syndrome and overlapping findings on imaging.
• Primary and secondary causes (1,2,3):
  • Primary:
    • Acute idiopathic eosinophilic pneumonia (AEP)
    • Chronic idiopathic eosinophilic pneumonia (CEP)
    • Eosinophilic granulomatosis with polyangiitis (EGPA) previously called Churg-Strauss syndrome (CSS) (4)
    • Simple pulmonary eosinophilia (SPE, i.e., Löffler syndrome) also overlaps pulmonary infiltrates with eosinophilia syndrome.
    • Hypereosinophilic syndromes (HES)
    • Eosinophilic bronchitis
  • Secondary causes: allergic bronchopulmonary aspergillosis (ABPA), parasitic infections, drug or toxin induced

Epidemiology

Incidence

• Uncommon in United States, rates not specifically reported
• CEP ~1–2% of all interstitial lung disease (ILD)

Prevalence

• Predominant age: varies depending on exact process
• Predominant sex:
  • AEP: male = female usually young patients
  • CEP: female > male (2:1), no difference after age 60 years
  • HES: male > female, 7:1 (3)
  • ABPA: 7–14% of all asthmatics, rare in nonasthmatics (5)

Etiology and Pathophysiology

• No single etiology for the diverse cluster of diseases
• Idiopathic (AEP, CEP)
• Hypersensitivity (ABPA, Löffler syndrome)
• Cigarette smoking (AEP)
• Heavy dust and other occupational exposures (AEP)
• Infectious: parasites, filariae, nematodes (Löffler syndrome), specifically Ascaris most common worldwide. Others include Strongyloides hookworms, filarial nematodes, Toxocara, and Paragonimus.
• Drug induced: 120 known associations; most common: NSAIDs, minocycline, nitrofurantoin, cocaine

Genetics
No known genetic pattern

Risk Factors

• Often idiopathic
• AEP
  • Drugs
  • Inhalation of toxic products
  • Cigarette smoking
• CEP
  • Drugs
  • Irradiation for breast cancer
  • Asthma
• ABPA (3,5)
  • Asthma (usual duration 8 to 12 years prior)
  • Cystic fibrosis

Commonly Associated Conditions

• Asthma (ABPA, EGPA)
• Cystic fibrosis (ABPA)
• Atopy (notable for CEP)
• Tobacco use (AEP)