Eosinophilic Pneumonitis: Definition, Diagnosis, and Management
Definition
Eosinophilic pneumonitis is a group of interstitial lung diseases characterized by abnormal accumulation of eosinophils in the alveolar spaces and lung interstitium, with or without peripheral blood eosinophilia. 1, 2
The condition manifests in three primary forms:
- Acute eosinophilic pneumonia (AEP): Rapid onset with respiratory failure potential, no relapse after treatment 3
- Chronic eosinophilic pneumonia (CEP): Marked tissue and peripheral eosinophilia, rapid steroid response, tendency to recur 3
- Löffler syndrome: Transient pulmonary infiltrates, typically parasitic etiology 1, 2
Diagnosis
Clinical Presentation
The diagnosis requires both characteristic clinical-imaging features AND demonstration of alveolar eosinophilia (≥25% eosinophils on bronchoalveolar lavage). 2
Key clinical features to identify:
- Respiratory symptoms: Dyspnea, cough, wheeze developing over days (AEP) to weeks-months (CEP) 1, 4
- Fever: Common in AEP, may mimic infectious pneumonia 2
- Peripheral blood eosinophilia: Frequently elevated but may be absent at presentation in AEP 1, 2
- Extrathoracic manifestations: Suggest systemic disease, particularly eosinophilic granulomatosis with polyangiitis 1, 2
- Airflow obstruction: Frequent in CEP and related conditions 1
Imaging Findings
Chest CT demonstrates bilateral pulmonary infiltrates in nonsegmental distribution. 5
Radiological patterns include:
- Patchy bilateral lung infiltrates on high-resolution CT 5
- Ground-glass opacities, consolidation, or nodular patterns 3
- Peripheral predominance typical in CEP 3
Laboratory and Procedural Workup
Bronchoalveolar lavage (BAL) is essential for diagnosis, demonstrating ≥25% eosinophils. 2
Required investigations:
- BAL fluid analysis: Cell count showing ≥25% eosinophils; cultures to exclude infection 5, 2
- Complete blood count: Peripheral eosinophilia common but not required 1, 2
- Infectious workup: BAL cultures for bacteria, fungi, Pneumocystis jirovecii, parasites 5
- Chest CT: More sensitive than radiographs for detecting infiltrates 5
Lung biopsy is NOT indicated except in atypical cases after multidisciplinary discussion. 1
When performed, histology shows:
- Eosinophilic infiltration of alveolar spaces and interstitium 5
- Tissue eosinophilia with chronic interstitial inflammation 5
- Overlap of patterns with lymphoid aggregates 5
Diagnostic Criteria
Apply these three criteria: (1) newly identified bilateral pulmonary opacities on imaging; (2) temporal association with drug/exposure initiation OR idiopathic presentation; (3) exclusion of other causes including infection, malignancy, and systemic disease. 5
Etiologic Investigation
Meticulous inquiry into possible causes is mandatory before labeling as idiopathic. 1, 2
Investigate systematically:
- Medications: Daptomycin, molecular targeting agents, immune checkpoint inhibitors 5, 4
- Toxic exposures: Marijuana, environmental toxins 6
- Infections: Parasites (most common for Löffler syndrome), fungi 1, 2
- Systemic diseases: Eosinophilic granulomatosis with polyangiitis if extrathoracic manifestations present 5, 1
Critical Pitfall
AEP may be misdiagnosed as severe infectious pneumonia because peripheral eosinophilia can be absent at presentation. 2 Maintain high suspicion in patients with rapid respiratory deterioration and bilateral infiltrates, particularly with recent drug initiation or exposure history.
Management
Acute Treatment
Corticosteroids are the cornerstone of therapy for all forms of eosinophilic pneumonia. 1
Treatment approach:
- Immediate drug cessation if drug-related pneumonitis identified 4
- High-dose systemic corticosteroids: Initiate promptly for AEP or symptomatic CEP 1, 3
- Rapid response expected: AEP responds quickly without relapse; CEP responds rapidly but relapses are common 3
Maintenance and Monitoring
For CEP, prolonged steroid therapy is required due to high relapse tendency. 3
- Steroid taper: Gradual reduction over months for CEP 1
- Monitor for relapse: Particularly in CEP patients 3
- Biologic therapies: Interleukin-5 targeted therapies increasingly used for refractory or relapsing disease 1
Special Considerations
In drug-related cases, dechallenge producing measurable improvement confirms diagnosis; rechallenge causes worsening but is often clinically impractical. 5
Multidisciplinary discussion involving pulmonologists, radiologists, and pathologists (if biopsy performed) is essential for diagnosis, particularly in atypical presentations. 5