Definition and epidemiology
The eosinophilic pneumonias are a group of disorders defined by accumulation of eosinophils in the lung parenchyma and airspaces, demonstrated by raised bronchoalveolar lavage (BAL) eosinophils or by lung biopsy, with or without peripheral blood eosinophilia. The two idiopathic forms are acute eosinophilic pneumonia (AEP) and chronic eosinophilic pneumonia (CEP). Both are uncommon in children. AEP can follow new exposures — notably tobacco or other inhalational triggers — and presents as a rapidly progressive febrile illness that may mimic severe pneumonia or ARDS. CEP is an indolent disorder more often associated with a history of atopy or asthma.
Clinical features
AEP presents over days to a few weeks with fever, dyspnoea, cough and pleuritic pain, frequently progressing to hypoxaemic respiratory failure; peripheral eosinophilia is often absent at onset, which is a diagnostic trap. CEP evolves over weeks to months with cough, progressive breathlessness, weight loss, night sweats and wheeze; peripheral eosinophilia is usually present and imaging classically shows peripheral (“photographic negative of pulmonary oedema”) infiltrates. CEP characteristically relapses when therapy is withdrawn.
Diagnosis
Diagnosis integrates the clinical tempo, imaging and — crucially — BAL eosinophil percentage. For AEP, the Philit criteria require an acute febrile illness ≤1 month, diffuse pulmonary infiltrates, BAL eosinophilia (typically ≥25%) or biopsy-proven eosinophilic pneumonia, and exclusion of infection, drug reaction and other eosinophilic disease. For CEP, supportive features are a symptom history beyond two months, a prolonged or relapsing course, peripheral and BAL eosinophilia, and characteristic peripheral consolidation. A general airway-eosinophilia threshold of >5% BAL eosinophils raises the possibility of eosinophilic lung disease. Always exclude secondary causes: parasitic infection, drugs, fungi (ABPA), and eosinophilic granulomatosis with polyangiitis.
See the full criteria: Eosinophilic Pneumonia
Red flags
- Rapidly progressive hypoxaemia or respiratory failure in suspected AEP
- Multisystem features (rash, neuropathy, sinusitis) suggesting EGPA or HES
- Eosinophilia with a relevant travel or exposure history — exclude parasites before steroids
- Failure to respond to corticosteroids — reconsider infection or malignancy
- Recurrent relapse on steroid taper (typical of CEP, but reassess the diagnosis)
Management overview
Both forms are exquisitely corticosteroid-responsive, and systemic corticosteroids are the cornerstone of treatment; AEP often improves dramatically within days. Provide supportive oxygen and escalate to respiratory support or critical care for AEP with severe hypoxaemia. Before committing to long courses of steroids, exclude infection and parasitic disease, since immunosuppression of an undiagnosed infection is harmful. CEP typically requires a prolonged, slowly tapered steroid course because of its high relapse rate, and steroid-sparing or biologic (anti-IL-5 class) agents may be considered in relapsing or steroid-dependent disease. Remove any identified trigger, including tobacco and culprit drugs, and arrange longitudinal follow-up with serial imaging and eosinophil counts.
References
- Philit F, et al. Idiopathic acute eosinophilic pneumonia. Am J Respir Crit Care Med, 2002.
- Carrington CB, et al. Chronic eosinophilic pneumonia. NEJM.
- Suzuki Y, Suda T. Acute and chronic eosinophilic pneumonia. Frontiers in Medicine, 2024.
- Nelson Textbook of Pediatrics, 21st ed.
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.