Histologic features--Desquamative interstitial pneumonia has recently been renamed alveolar macrophage pneumonia.47 AMP (DIP) is now considered to be primarily a smoking-related illness.1, 10, 48, 49 AMP (DIP) may represent the most severe manifestation of smoking-related changes of the small airways and lung parenchyma. At the mild end of the spectrum of airway-related changes secondary to cigarette smoke is respiratory bronchiolitis; respiratory bronchiolitis-associated interstitial lung disease represents more severe airway inflammation due to cigarette smoke,10, 49-52 with limited amounts of peribronchiolar inflammation accompanying alveolar macrophage accumulation. The characteristic histologic finding of AMP (DIP) is alveolar accumulation of macrophages.2, 53 Minimal inflammatory cell infiltration and fibrosis may also be present. AMP (DIP) is distinguished from UIP by the fact that the former is a temporally uniform process that is not accompanied by fibroblastic foci, unlike UIP. Also, macrophage accumulation in AMP (DIP) is diffuse, whereas in UIP, it is focal. AMP (DIP) used to be thought of as early stage UIP, but the two are now considered to be separate entities.
Clinical findings--AMP (DIP) is essentially a rare disease of smokers. The peak incidence occurs in patients 30 to 50 years of age. Most patients present with dyspnea. In general, symptoms are more acute with DIP than with UIP. Pulmonary function testing may reveal a restrictive pattern with decreased diffusing capacity.2 Hypoxemia may be present. PFT abnormalities tend to be less severe than patients with UIP. The prognosis for patients with AMP (DIP) is quite favorable. The 10-year survival is about 70%.
RB-ILD is also a disease of heavy smokers. These patients typically have shortness of breath and cough. The prognosis of RB-ILD is excellent. Progression to end-stage lung fibrosis does not occur.
Radiographic findings--Chest radiographs: The chest radiograph in cases of AMP (DIP) may reveal ground glass opacity or air space consolidation, particularly in a basilar and subpleural distribution (figure 7 -- 36KB).10 Patients with AMP (DIP) are more likely to demonstrate ground glass opacity than patients with UIP. Irregular linear opacities, often lower lung predominant, may also be seen. Nodules, adenopathy, and effusion are all uncommon. A normal chest radiograph has been reported in 3% to 22% cases.10, 54, 55
The chest radiograph in RB-ILD typically demonstrates bilateral, mid and lower lung predominant linear and reticular opacities, frequently associated with bronchial wall thickening. Honeycombing is not present (figure 8 -- 44KB).
HRCT: HRCT findings of AMP (DIP) include basilar, subpleural, lower lobe predominant ground glass opacity and irregular reticular opacities (figure 9 -- 63KB).10, 56 Although the spectrum of findings of AMP (DIP) and UIP overlap, ground glass opacity is more commonly seen with AMP (DIP) than UIP.57 Up to half of patients with AMP (DIP) may show reticulation,49 and honeycombing may be seen in 30%. Compared to UIP, findings that suggest fibrosis are relatively mild.3, 57 The HRCT findings of AMP (DIP) may improve with treatment.58, 59
HRCT findings of RB-ILD typically include patchy areas of ground glass opacity, perhaps accompanied by airway thickening (figure 10 -- 51KB). Nodules, interlobular septal thickening, effusions, and adenopathy are uncommon.
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