What are the diagnostic criteria for Eosinophilic pneumonia?

Diagnostic Criteria for Eosinophilic Pneumonia

The diagnosis of eosinophilic pneumonia requires a combination of clinical, radiological, and pathological findings, with bronchoalveolar lavage (BAL) showing >25% eosinophils being the most definitive diagnostic criterion. 1

Clinical Presentation

• Acute eosinophilic pneumonia (AEP) presents with acute respiratory insufficiency, hypoxemia, fever, and diffuse radiographic infiltrates developing over 2-21 days 2
• Chronic eosinophilic pneumonia (CEP) has a more prolonged course with symptoms present for more than 2 months prior to diagnosis 3
• Common symptoms include dyspnea, cough, myalgias, and fever 2, 4

Diagnostic Criteria

Essential Criteria

• Pulmonary symptoms (dyspnea, cough) with respiratory insufficiency 2, 4
• Characteristic radiographic abnormalities:
  • AEP: Bilateral diffuse infiltrates 2
  • CEP: Peripheral "photographic negative of pulmonary edema" pattern in approximately 28% of cases 5
• Marked eosinophilia in bronchoalveolar lavage fluid (>25% eosinophils) 1, 5
• Exclusion of other causes of pulmonary eosinophilia 1, 4

Supporting Criteria

• Peripheral blood eosinophilia (present in 86% of CEP cases, but may be absent in early AEP) 5
• Elevated serum IgE levels 1
• Rapid response to corticosteroid therapy (typically within 4 days) 2
• Histopathologic findings:
  • AEP: Acute and organizing diffuse alveolar damage with prominent interstitial and alveolar eosinophils 2
  • CEP: Eosinophilic infiltration in transbronchial lung biopsy (positive in 64% of cases) 5

Diagnostic Approach

1. Imaging studies:

   • High-resolution CT of the chest to demonstrate "fluffy" or nodular migratory pulmonary infiltrates, peripheral nodules (25%), ground glass opacities (86%), and bronchial wall thickening/bronchiectasis (66%) 6

2. Bronchoscopy with BAL:

   • Essential for diagnosis, showing marked eosinophilia (>25% eosinophils) 1
   • Should include cell differential count, culture for infectious organisms, and cytology to exclude malignancy 1
   • BAL is the single most sensitive test for detecting eosinophilia (100% in CEP) 5

3. Laboratory testing:

   • Complete blood count with differential to assess peripheral eosinophilia 5
   • Serum IgE levels (often elevated) 1
   • ANCA testing to exclude vasculitis 6

4. Lung biopsy:

   • Transbronchial lung biopsy may show eosinophilic infiltration (positive in 64% of CEP cases) 5
   • Histopathology shows eosinophilic inflammation and infiltration 6

Differential Diagnosis

• Exclusion of secondary causes is necessary before confirming diagnosis:
  • Parasitic infections 1, 4
  • Drug reactions 1
  • Malignancy 1
  • ANCA-associated vasculitis 6
  • Allergic bronchopulmonary aspergillosis 6
  • Idiopathic hypereosinophilic syndrome 6

Classification

• Acute eosinophilic pneumonia:

  • Less than one month history of symptoms prior to diagnosis
  • Short clinical course
  • No recurrence 3

• Chronic eosinophilic pneumonia:

  • More than two months history of symptoms prior to diagnosis
  • Prolonged clinical course
  • Tendency to recur 3

Diagnostic Pitfalls

• Peripheral blood eosinophilia may be absent in early stages of AEP, making BAL essential for diagnosis 2, 5
• The characteristic radiographic pattern of CEP (peripheral infiltrates) is present in only about 28% of cases at initial examination 5
• Multiple diagnostic tests may be needed as positivity rates vary: peripheral blood (86%), BAL (100%), and TBLB (64%) 5
• All three diagnostic methods (peripheral blood, BAL, and TBLB) are positive for eosinophilia in only 60% of patients 5