Eosinophilic lung diseases are a heterogenous group of disorders that are characterized by excess infiltration of eosinophils within the lung interstitium and alveoli and are broadly divided into three main groups 1:
- idiopathic: unknown causes
- secondary: known causes
- eosinophilic vasculitis: eosinophilic granulomatosis with polyangiitis
Diagnosis is made based on one of the following:
- pulmonary opacities on a chest radiograph or HRCT chest with peripheral eosinophilia
- tissue eosinophilia at either open or transbronchial lung biopsy
- increased eosinophils in bronchoalveolar lavage (BAL) fluid
Simple pulmonary eosinophilia (SPE)
Simple pulmonary eosinophilia (also known as Loffler syndrome) is a benign and self-limiting condition, characterized by mild symptoms and plain radiographic findings usually much more impressive than the patient's condition, and classically have a reverse bat's wing appearance. Blood eosinophilia is a feature.
Acute eosinophilic pneumonia (AEP)
Acute eosinophilic pneumonia (AEP) usually manifests with acute onset fever, severe dyspnea and hypoxia for <5 days with rapid progression and shows rapid improvement when treated with steroids and usually no relapse after treatment. Pulmonary lavage reveals >25% eosinophils, however peripheral blood eosinophil counts are usually normal. The etiology of AEP is unknown. It has been suggested that it may represent acute hypersensitivity to an inhaled antigen. CT findings include bilateral patchy areas of ground-glass opacity and interlobular septal thickening.
Chronic eosinophilic pneumonia (CEP)
Chronic eosinophilic pneumonia is characterized by homogeneous peripheral airspace consolidation lasting >6 months, which responds to steroid treatment. This appearance results in a reverse bat's wing appearance. About 50% of patients with CEP have asthma. CEP may be difficult to differentiate from Churg-Strauss syndrome (CSS). While CEP has homogeneous peripheral airspace consolidations, the consolidations in CSS tends to be more lobular in distribution. In addition, CSS tends to have centrilobular nodules.
Idiopathic hypereosinophilic syndrome (IHS)
Idiopathic hypereosinophilic syndrome is a systemic disorder with damage to heart and the CNS. On CT, one finds nodules with a ground-glass halo, similar to SPE. In contrast to SPE, the opacities do not resolve spontaneously. In addition, approximately 50% of cases are associated with pleural effusions.
These cases have non-specific findings on chest radiography and CT. Offending drugs include:
- nitrofurantoin (which may progress to pulmonary fibrosis)
Allergic bronchopulmonary aspergillosis (ABPA)
Bronchocentric granulomatosis (BG)
Bronchocentric granulomatosis (BG) is a rare disorder with non-specific radiographic findings. Approximately two-thirds of cases are not associated with tissue eosinophilia. The remaining one-third have peripheral eosinophilia, asthma, fungal hyphae at biopsy and positive sputum cultures for Aspergillus.
Eosinophilic granulomatosis with polyangiitis (EGPA)
Eosinophilic granulomatosis with polyangiitis (EGPA), previously known as Churg-Strauss syndrome, is associated with CT findings similar to CEP. Like CEP, CSS is seen in asthma patients. In contrast to CEP, the subpleural consolidations tend to have a lobular distribution and tend to be migratory or transient. In addition, centrilobular nodules are found on CT.
- 1. Jeong YJ, Kim KI, Seo IJ et-al. Eosinophilic lung diseases: a clinical, radiologic, and pathologic overview. Radiographics. 27 (3): 617-37. doi:10.1148/rg.273065051 - Pubmed citation
- 2. Johkoh T, Müller NL, Akira M et-al. Eosinophilic lung diseases: diagnostic accuracy of thin-section CT in 111 patients. Radiology. 2000;216 (3): 773-80. Radiology (full text) - Pubmed citation