Eosinophilic lung disease

Eosinophilic lung diseases are a heterogeneous group of disorders that are characterised 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 

Pathology

Idiopathic 

Simple pulmonary eosinophilia (SPE)

Simple pulmonary eosinophilia (also known as Löffler syndrome) is a benign and self-limiting condition, characterised 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 dyspnoea 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 aetiology 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 characterised 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 eosinophilic granulomatosis with polyangiitis (EGPA).

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.

Secondary

Drugs 

These cases have non-specific findings on chest radiography and CT. Offending drugs include:

• antibiotics

  • nitrofurantoin (which may progress to pulmonary fibrosis)

  • penicillin

  • tetracycline

• toxins

  • eosinophilia-myalgia syndrome from contaminated L-tryptophan

  • toxic oil syndrome

See also: drug rash with eosinophilia and systemic symptoms (DRESS).

Infection

• fungal

  • Aspergillus fumigatus (asthmatic pulmonary eosinophilia)

• parasitic

  • schistosomiasis (50% have pulmonary involvement)

  • ascariasis

  • Toxocara canis

  • microfilariasis (Tropical pulmonary eosinophilia)

  • strongyloidiasis - pulmonary strongyloidiasis

Allergic bronchopulmonary aspergillosis (ABPA)

ABPA is not a fungal infection, but rather a hypersensitivity response to fungal allergens. CT findings include bronchiectasis involving the central and upper lungs with or without mucoid impaction.

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 vasculitis

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, EGPA is seen in asthma patients. In contrast to CEP which has homogeneous peripheral airspace consolidations, the subpleural consolidations in EGPA tend to have a lobular distribution and tend to be migratory or transient. In addition, centrilobular nodules are found on CT.