Desquamative Interstitial Pneumonia/Respiratory Bronchiolitis-Associated Interstitial Lung Disease

Clinical features: Patients with desquamative interstitial pneumonia (DIP) tend to be younger, have a lower mortality rate, and have a better response to steroids than those with UIP. Most patients are cigarette smokers. Occasionally, there may be complete recovery [1]. Recurrence after unilateral lung transplantation was reported in one case [2]

HRCT Changes in DIP

HRCT at the lung bases shows patchy ground-glass density bilaterally. Note some regions of normal lung, especially posteriorly in the LLL. At the posterior RLL, one can appreciate a fine net-like or reticular pattern asssociated with the abnormal ground-glass opacity (arrow). The reticular pattern represents thickened interlobular and intralobular septa, the latter probably representing bronchiolovascular structures. Note the absence of honeycombing.

Contrast this CT with that of UIP.

This pattern is an excellent example of DIP, but a similar pattern can also be seen with NSIP, atypical pneumonias, pulmonary hemorrhage, ARDS/edema, alveolar proteinosis, and hypersensitivity pneumonia.

In a study of 22 patients (mean age 43), subpleural ground-glass opacities predominated in 13. Middle and lower lung zones were involved in all patients and the upper lung zone in 18. Irregular lines were present in 11 and cystic changes in 7. The distribution of opacities resembled that of UIP, but the greater ground-glass component and the minimal cystic change distinguish it from UIP [3]. In a study of the CTs of 11 patients over time, the initial films showed ground-glass attenuation involving a mean of 51% of the lung, 5 patients also had irregular lines (involving 5%), and 1 patient had honeycombing. After a median of 10 months of treatment, six patients showed a decrease in ground-glass opacities, three remained stable, one showed progression to irregular lines, and one to honeycombing [4].

Histopathologic changes of DIP

1. Low-power temporal and spatial uniformity

2. Filling of small airways and alveolar spaces by macrophages with finely granular, yellow-brown pigment

3. Slight widening of alveolar walls by chronic inflammatory cells and little fibrosis

4. Type II cell hyperplasia

 

 

DIP--higher magnification

Here, the alveolar macrophages appear to blend with the interstitium. The clustered macrophages have abundant pink cytoplasm, and the interstitium contains vessels and lymphoid cells with little fibrosis. Type II cell hyperplasia is minimal. Try to trace the alveolar walls to verify the intact architecture.

PAS stain after diastase digestion

Note that the macrophages in the alveolar space shown here have cytoplasmic PAS-D positivity that corresponds to the light brown pigment described in H&E stains. Stains for iron are negative or faintly positive, indicating that the brown pigment is not hemosiderin. It probably represents an accumulation of lysosomes with undigested debris.

Respiratory bronchiolitis-associated interstitial lung disease--RBILD

There is controversy as to whether RBILD is part of the spectrum of DIP or a separate entity [1,5]. Both occur mainly in cigarette smokers. Most heavy smokers have some chronic bronchiolitis and respiratory bronchiolitis. In a few, however, the changes can be quite pronounced, and the patient complains of dyspnea, cough, and sputum production. The chest radiograph may show a reticular pattern. Histologically, the changes are similar to those described above for DIP, but they are confined to the peribronchiolar region, rather than being diffuse. Symptoms usually diminish if the patient stops smoking; sometimes corticosteroids are used. Progression of disease has not been noted [5].

References

1. Katzenstein A-L, Myers J. Idiopathic pulmonary fibrosis. Clinical relevance of pathologic classification. Am J Respir Crit Care Med 1998; 157:1301-1315.

2. King M, Jessurun J, Hertz M. Recurrence of desquamative interstitial pneumonia after lung transplantation. Am J Respir Crit Care Med 1997; 156:2003-2005.

3. Hartman T, Primack S, Swensen S, Hansell D, McGuinness G, Müller N. Desquamative interstitial pneumonia: thin-section CT findings in 22 patients. Radiology 1993; 187:787-790.

4. Hartman T, Primack S, Kang E-Y, Swensen S, Hansell D, McGuinness G, Müller N. Disease progression in usual interstitial pneumonia compared with desquamative interstitial pneumonia. Assessment with serial CT. Chest 1996; 110:378-382.

5. Yousem S, Colby T, Gaensler E. Respiratory bronchiolitis-associated interstitial lung disease and its relationship to desquamative interstitial pneumonia. Mayo Clin Proc 1989; 64:1373-1380.

Clinical summary Discussion

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