Pulmonary eosinophilia
- Lesion
A group of lung diseases where eosinophils fill the alveoli and septa, caused by parasites, drugs, fungi, vasculitis or no known cause.
What it is
Pulmonary eosinophilia covers disorders in which eosinophils infiltrate the lung, usually through IL-5 from T cells. Some are transient and harmless (Löffler syndrome), others cause acute respiratory failure or chronic illness. Parasites, drugs, Aspergillus and vasculitis (EGPA) are the causes to look for; in many cases none is found.
Structure
- Alveolar septa thickened by eosinophils; alveoli filled with eosinophils and macrophages.
- Eosinophilic microabscesses and Charcot-Leyden crystals may be present.
- Acute eosinophilic pneumonia: diffuse alveolar damage with many eosinophils.
- EGPA: necrotising small-vessel vasculitis with eosinophil-rich granulomas.
Step by step
- An antigen (larva, drug, fungus) or unknown trigger activates Th2 cells.
- IL-5 drives eosinophil production in the marrow and their recruitment to the lung.
- Eosinophils degranulate (major basic protein, cationic protein) and injure the alveolar wall.
- If the trigger is removed (larvae move on, drug stopped) infiltrates clear; otherwise inflammation persists.
- In EGPA, the eosinophilic inflammation also involves small vessels.
Main eosinophilic lung diseases
| Disease | Course | Key clue |
|---|---|---|
| Löffler syndrome | Transient, migratory | Larval migration of intestinal worms |
| Acute eosinophilic pneumonia | Days; respiratory failure | Recent start of smoking |
| Chronic eosinophilic pneumonia | Weeks to months | Peripheral infiltrates, asthma history |
| Eosinophilic granulomatosis with polyangiitis | Chronic, systemic | Asthma, eosinophilia, vasculitis, often ANCA |
| Allergic bronchopulmonary aspergillosis | Chronic, relapsing | Asthma or CF, high IgE, central bronchiectasis |
Clinical notes
- Ask about travel, parasites, new drugs, smoking and asthma; check blood eosinophils and IgE.
- Strongyloides must be excluded before steroids because hyperinfection can be fatal.
- Most forms respond rapidly to corticosteroids.
Test yourself
Think of the answer, then tap the question to see it.
What causes Löffler syndrome?
Usually larvae of intestinal nematodes such as Ascaris or Strongyloides migrating through the lung, producing transient infiltrates and blood eosinophilia.
What is the typical chest image of chronic eosinophilic pneumonia?
Peripheral infiltrates, the reverse of the central pattern of pulmonary edema.
Which infection must be excluded before giving steroids for eosinophilic lung disease?
Strongyloides stercoralis, because steroids can trigger fatal hyperinfection.
Connections
Microorganisms2
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Interstitial Lung Diseases (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.