[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Lung](https://durgical.com/en/general-pathology/areas/lung/) › Pulmonary eosinophilia

# 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.

Updated Nov 12, 2026

## Key points

- Simple eosinophilia (Löffler syndrome): transient, migratory infiltrates with blood eosinophilia, often from larvae passing through the lung (Ascaris, Strongyloides, hookworm).
- Tropical eosinophilia: microfilariae (filarial infection).
- Acute eosinophilic pneumonia: abrupt fever and respiratory failure, often after starting to smoke; responds promptly to steroids.
- Chronic eosinophilic pneumonia: peripheral infiltrates ('photographic negative' of pulmonary edema), fever, night sweats, weight loss.
- Secondary: drugs, ABPA, eosinophilic granulomatosis with polyangiitis (asthma, eosinophilia, vasculitis).

## 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](https://durgical.com/en/conditions/eosinophilic-pneumonias/) | Transient, migratory | Larval migration of intestinal worms |
| [Acute eosinophilic pneumonia](https://durgical.com/en/conditions/eosinophilic-pneumonias/) | Days; respiratory failure | Recent start of smoking |
| [Chronic eosinophilic pneumonia](https://durgical.com/en/conditions/eosinophilic-pneumonias/) | Weeks to months | Peripheral infiltrates, asthma history |
| [Eosinophilic granulomatosis with polyangiitis](https://durgical.com/en/conditions/eosinophilic-granulomatosis-with-polyangiitis/) | Chronic, systemic | Asthma, eosinophilia, vasculitis, often ANCA |
| [Allergic bronchopulmonary aspergillosis](https://durgical.com/en/conditions/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.

## Memory aid

Worms, wheezing, drugs and fungi: the four doors that let eosinophils into the lung.

## 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.

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## Connections

## Related 3

- [Asthma: pathology](https://durgical.com/en/general-pathology/asthma-pathology/)
- [Drug- and radiation-induced lung injury](https://durgical.com/en/general-pathology/drug-and-radiation-induced-lung-injury/)
- [Hypersensitivity pneumonitis](https://durgical.com/en/general-pathology/hypersensitivity-pneumonitis/)

## Related conditions 3

- [Eosinophilic pneumonias (including Löffler syndrome)](https://durgical.com/en/conditions/eosinophilic-pneumonias/)
- [Eosinophilic granulomatosis with polyangiitis (Churg–Strauss)](https://durgical.com/en/conditions/eosinophilic-granulomatosis-with-polyangiitis/)
- [Allergic bronchopulmonary aspergillosis (ABPA)](https://durgical.com/en/conditions/allergic-bronchopulmonary-aspergillosis/)

## Microorganisms 2

- [Ascaris lumbricoides](https://durgical.com/en/microbiology/ascaris-lumbricoides/)
- [Strongyloides stercoralis](https://durgical.com/en/microbiology/strongyloides-stercoralis/)

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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](https://medlineplus.gov/interstitiallungdiseases.html) (MedlinePlus, US National Library of Medicine, 2025).

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Source: https://durgical.com/en/general-pathology/pulmonary-eosinophilia/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/pulmonary-eosinophilia/