- Overview of Interstitial Lung Disease
- Drug-Induced Pulmonary Disease
- Overview of Eosinophilic Pulmonary Diseases
- Acute Eosinophilic Pneumonia
- Chronic Eosinophilic Pneumonia
- Löffler Syndrome
- Hypersensitivity Pneumonitis
- Overview of Idiopathic Interstitial Pneumonias
- Idiopathic Pulmonary Fibrosis (IPF)
- Desquamative Interstitial Pneumonia (DIP)
- Nonspecific Interstitial Pneumonia (NSIP)
- Cryptogenic Organizing Pneumonia (COP)
- Respiratory Bronchiolitis–Associated Interstitial Lung Disease (RBILD)
- Acute Interstitial Pneumonia (AIP)
- Lymphoid Interstitial Pneumonia (LIP)
- Idiopathic Pleuroparenchymal Fibroelastosis
- Lymphangioleiomyomatosis
- Pulmonary Alveolar Proteinosis
- Pulmonary Langerhans Cell Histiocytosis
Eosinophilic pulmonary diseases are a heterogeneous group of disorders characterized by the accumulation of eosinophils in alveolar spaces, the interstitium, or both. Peripheral blood eosinophilia (eosinophil counts > 500 cells/mcL [ 0.5 × 109/L]) is also common. Known causes of eosinophilic pulmonary disease include the following:
Drug-induced pneumonitis (eg, caused by medications, such as antibiotics, phenytoin)(eg, caused by medications, such as antibiotics, phenytoin)
Infections (especially helminthic infections)
Inhaled toxins (eg, illicit drugs, such as cocaine)
Systemic disorders (eg, eosinophilic granulomatosis with polyangiitis)
Often the cause is unknown.
The 2 primary eosinophilic pulmonary diseases of unknown etiology are:
Hypereosinophilic syndrome, a systemic disease affecting multiple organs, is discussed elsewhere.
Löffler syndrome, a syndrome of fleeting pulmonary findings and peripheral blood eosinophilia, is another eosinophilic pulmonary disease.
Diagnosis of Eosinophilic Pulmonary Diseases
Chest radiograph or CT scan of the chest
Demonstrating eosinophilia in peripheral blood, bronchoalveolar lavage fluid, or lung tissue
Diagnosis is based on the demonstration of opacities on chest imaging and identification of eosinophilia (> 500 eosinophils/mcL [0.5 × 109/L]) in peripheral blood, bronchoalveolar lavage fluid, or lung biopsy tissue. However, pulmonary eosinophilia may occur in the absence of peripheral eosinophilia.
Eosinophils are exquisitely sensitive to glucocorticoids and completely disappear from the bloodstream within a few hours after administration of glucocorticoids. This rapid disappearance from the blood may obscure the diagnosis in patients who receive glucocorticoids before the diagnostic assessment is performed.
Eosinophils are primarily tissue-dwelling and are several hundred–fold more abundant in tissues than in blood. Consequently, blood eosinophil numbers do not necessarily indicate the extent of eosinophilic involvement in affected tissues. Eosinophils are most numerous in tissues with a mucosal epithelial interface with the environment, such as the respiratory, gastrointestinal, and lower genitourinary tracts. Eosinophils are not present in the lungs of healthy people, so their presence in tissue or bronchoalveolar lavage fluid (> 10%) indicates a pathologic process (1). Pulmonary opacities on chest imaging associated with blood eosinophilia are sometimes called PIE (pulmonary infiltrates with eosinophilia) syndrome.
Reference
1. Rosenberg CE, Khoury P. Approach to Eosinophilia Presenting With Pulmonary Symptoms. Chest 2021;159(2):507-516. doi:10.1016/j.chest.2020.09.247
