Chapter 71: The Eosinophilic Pneumonias

Introduction

The association between pulmonary infiltrates and eosinophilia was first identified by Loeffler in 1932. It is now recognized that the eosinophilic pneumonias are a heterogeneous group of disorders characterized by varying degrees of pulmonary parenchymal and/or blood eosinophilia.¹ The precise role that eosinophils play in the pathogenesis of the different eosinophilic pneumonias is not clear. Normally, less than 2% of the leukocyte cell differential in bronchoalveolar lavage (BAL) are eosinophils. The presence of increased BAL and/or tissue eosinophils, and our knowledge of the biology of eosinophils (see Chapter 22) does, however, suggest that they play a variety of roles, including initiation, perpetuation, and amplification of tissue inflammation and injury. These effector functions are no doubt the result of the ability of the eosinophils to release numerous soluble mediators, including granule-derived proteins, arachidonic acid metabolites, proinflammatory cytokines, superoxide anions, metalloproteases, and hydroxyl radicals. The different roles of eosinophils in these disorders can be appreciated when comparisons are made of parasitic infections and disorders such as asthma or allergic bronchopulmonary aspergillosis (ABPA). In the former, eosinophils play a crucial role in eradicating the infectious pathogen; in the latter, the eosinophils accumulate in the lung as a result of immune hypersensitivity and are prominent mediators of tissue injury.

The spectrum of diseases that can be primarily or secondarily associated with blood or pulmonary eosinophilia is shown in Table 71-1. It is beyond the scope of this chapter to discuss each of these disease entities in detail. Instead, discussion will focus on diseases of known or unknown causes in which eosinophilic infiltration of lung tissue is a characteristic feature, including acute eosinophilic pneumonias, tropical pulmonary eosinophilia (TPE), chronic eosinophilic pneumonia (CEP), ABPA, Churg–Strauss syndrome (now termed as eosinophilic granulomatosis with polyangiitis [EGPA]), and idiopathic hypereosinophilic syndrome (HES). Since eosinophilic granuloma of the lung is frequently seen in the absence of blood or tissue eosinophilia, it is considered separately (Chapter 74).

Eosinophilic Pneumonias With Acute Presentations

Acute presentations of eosinophilic pneumonia center on several primary considerations, including Loeffler Syndrome, parasitic infections, drug- and toxin-related disorders, and idiopathic ...