Ground-glass attenuation in patients with PLCH correlates with the presence of RB-DIP-like changes highlighting the concept that PLCH, RB, and DIP form a spectrum of injury in cigarette smokers.51
AEP may be mistaken for other diseases including severe community-acquired pneumonia and acute respiratory distress syndrome (ARDS). Distinguishing AEP from ARDS is crucial given the differing responses to corticosteroids. Those with AEP respond rapidly to steroids whereas those with ARDS do not benefit and have a poor prognosis.
AEP shows findings of diffuse alveolar damage coupled with interstitial and alveolar infiltrates of eosinophils. Diffuse alveolar damage is a pattern of acute lung injury characterized in the acute phase by hyaline membranes, interstitial and intra-alveolar edema, patchy type ll pneumocyte hyperplasia, and microthrombi (Fig. 11C). The acute phase forms a continuum with the organizing phase in which proliferation of interstitial fibroblasts, organizing alveolar exudates, and prominent type ll pneumocyte hyperplasia are the histologic hallmarks.
On chest radiography those with AEP demonstrate bilateral reticular opacities, commonly with Kerley B (septal) lines. There is rapid progression over hours to days with increasing bilateral areas of patchy or diffuse consolidation. Computed tomography scans demonstrate bilateral areas of ground-glass, consolidation and septal thickening (Fig. 11).54 Unilateral or bilateral pleural effusions are present at some point during the course of the illness in all patients. The radiologic findings are similar to those of pulmonary edema although the heart size is usually normal. The radiologic differential includes ARDS, although septal lines are less common, pulmonary hemorrhage and infection.
Pigmented macrophages are found in and around the airways of all cigarette smokes. Those same macrophages may have a more extensive distribution and those patients currently carry the label of DIP. Dyspneic smokers who come to clinical attention demonstrate varying combinations of emphysema, airway inflammation/fibrosis, and alveolar wall fibrosis in addition to changes of PLCH. AEP is a dramatic response to recent-onset smoking seen in a small number of individuals. The interconnected pathways that lead to lung inflammation and fibrosis in cigarette smokers are slowly coming into focus (Fig. 1).2,3
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