A case of desquamative interstitial pneumonia progressing to "honeycomb lung"

Desquamative interstitial pneumonia may progress to lung fibrosis as characterized radiologically

BACKGROUND AND OBJECTIVE

In some patients, desquamative interstitial pneumonia may progress to lung fibrosis. The aim of this study was to assess the long-term radiological follow-up results in patients with desquamative interstitial pneumonia.

METHODS

Among 75 patients suspected of having desquamative interstitial pneumonia, 31 who fulfilled the criteria were included in this study. Clinical characteristics at presentation, responses to treatment and long-term follow-up were evaluated.

RESULTS

The 31 patients were predominantly males (94%), and the mean age was 55 years; 93% (28/30) had a history of smoking. The clinical findings included high serum levels of lactate dehydrogenase and immunoglobulin G. Bronchoalveolar lavage (26 patients, 84% of cases) frequently showed an increased percentage of eosinophils (mean 17%). Computed tomography (CT) or high resolution (HR) CT at presentation showed ground glass opacities and/or consolidation in all patients, with one third of patients also showing thin-walled cysts within the ground glass opacities. There was no honeycombing on CT or HRCT scans at presentation. Corticosteroid therapy was effective early in the course of the disease; long-term follow-up (mean 99 months) of 31 patients showed only one death due to progression of the disease, but long-term follow-up of 14 patients (mean 125 months) by HRCT showed the development of new thin-walled cysts and honeycombing in five and lung cancer in four patients, respectively.

CONCLUSIONS

In a proportion of patients, desquamative interstitial pneumonia may progress to lung fibrosis with honeycombing on HRCT, despite therapy.

Pathology of interstitial lung disease

A large and diverse group of pathologic conditions manifests clinically and radiologically as diffuse parenchymal lung disease. Diffuse interstitial lung diseases (ILDs) encompass mainly inflammatory processes that involve the structural elements of this organ. Some ILDs are caused by infections, but most are the result of immunologic, environmental, or toxic mechanisms. Currently, less morbid sampling techniques have increased dramatically the probability that pulmonologists will be faced with establishing a specific and clinically relevant diagnosis using surgical lung biopsy material. Most of the concepts presented in this article have been established using this type of specimen. In the early years of surgical lung biopsy, a small number of diffuse inflammatory conditions came to light that exclusively involved the lungs and did not seem to be caused by infection, toxin, sarcoidosis, pneumoconiosis, or neoplasm. In this article, these idiopathic disorders are discussed in the context of their dominant pathologic findings rather than presented as a separate group of entities.

Serial computed tomographic evaluation in desquamative interstitial pneumonia

BACKGROUND

Desquamative interstitial pneumonia (DIP) may represent the early stage and usual interstitial pneumonia (UIP) the late stage of the same disease. The purpose of this study was to evaluate the computed tomographic (CT) features of DIP, to evaluate the changes in pattern and extent of disease over time, and to determine whether the appearances of DIP on the CT scan change to those of UIP during follow up.

METHODS

Sequential CT evaluation was conducted on eight patients with DIP over a mean (SD) follow up period of 3.2 (1.3) years (range 1.6-6.5). The relative extents of ground glass and honeycombing were determined from serial CT scans. Changes in the extent and appearance of the disease were examined in paired anatomically comparable CT sections.

RESULTS

Common features on the CT scans of patients with DIP were a homogeneous increase in lung attenuation (n = 5), linear areas of attenuation (n = 5), relatively well preserved lung architecture (n = 5), and the presence of small cysts (n = 6). Uncommon features were architectural distortion (n = 3), and traction bronchiectasis (n = 1). In six patients with DIP with cystic spaces these did not change with time in three cases, in two they regreased, and in one patient they increased. Open lung biopsy samples from patients with DIP with many cystic lesions showed dilated alveolar ducts and bronchioles and/or pulmonary cysts, as well as numerous macrophage-filled air spaces and mild fibrosis, but no typical honeycomb cysts were seen.

CONCLUSIONS

Some of the microcysts in DIP are different from the honeycomb cysts seen in UIP, and some of the cysts seen in patients with DIP resolve with time. DIP does not progress to UIP in the short term.

Natural history and treated course of usual and desquamative interstitial pneumonia

Patients with confirmed interstitial pneumonia were initially classified histologically into "desquamative" (n = 40) and "usual" (n = 53) types, and followed for one to 22 years. Both the diagnosis and the extent of fibrosis affected the course and response to therapy. Mortality in desquamative interstitial pneumonia was 27.5 per cent, and mean survival 12.2 years, as compared with 66.0 per cent and 5.6 years in usual interstitial pneumonia (P less than 0.01). Without treatment, 21.9 per cent with the desquamative but none with the usual type improved. With corticosteroid therapy, 61.5 per cent with desquamative and only 11.5 per cent with usual interstitial pneumonia improved, whereas 27.0 per cent and 69.2 per cent worsened. We conclude that the histologic classification of chronic interstitial pneumonia used here permits forecasts of prognosis and response to treatment that cannot be deduced from other data.

Morphology and pathogenesis of desquamative interstitial pneumonitis

Thirty human lung biopsy specimens have been diagnoses as desquamative interstitial pneumonitis. Six cases had intraalveolar lesions, believed to be early, while 20 had advanced disease characterised by intraalveolar cellular clumps, alveolar wall fibrosis, distortion, and loss of pulmonary parenchyma. Electron microscopy, high resolution light microscopy, and cytological examination have shown that the characteristic clumps in the alveolar air spaces are formed predominantly by enlarged and aggregated macrophages. Lymphocytes and eosinophils are also present in the intraalveolar clumps and in alveolar walls. Inflammation and immunological mechanisms are suggested as causes of the cellular clumping. Interstitial pneumonitis, alveolar wall fibrosis, changes in the alveolar epithelium, and loss of lung parenchyma are believed to be secondary events.