Smoking-Related Interstitial Fibrosis (SRIF) in Patients Presenting With Diffuse Parenchymal Lung Disease

OBJECTIVES

To describe the clinical, radiologic, and pathologic findings in cases where smoking-related interstitial fibrosis (SRIF) was diagnosed in surgical lung biopsy specimens from patients with clinical and imaging features of diffuse parenchymal lung disease (DPLD).

METHODS

Cases were included in this study if patients had clinical and imaging evidence of DPLD and surgical lung biopsy specimens revealed SRIF. A dedicated multidisciplinary conference was held to correlate clinical, radiologic, and pathologic findings.

RESULTS

Six cases met inclusion criteria; all six (five women/one man, aged 42-57 years, mean age 47 years) were either current smokers (five of six) or ex-smokers (one of six) and were evaluated for respiratory symptoms and abnormal pulmonary function tests, most commonly reduced forced vital capacity (n = 3) and diffusing capacity for carbon monoxide (n = 6). The most common imaging abnormalities were bilateral ground-glass opacities, which correlated with histopathologic SRIF. Follow-up of up to 10 years showed stable or improved clinical symptoms, pulmonary function tests, and radiologic findings with smoking cessation (three patients) or a decrease in smoking (three patients). No specific treatments were given, and those treated with empiric corticosteroid tapers did not show discernible responses.

CONCLUSIONS

SRIF can present as clinically meaningful diffuse parenchymal lung disease in relatively young heavy smokers, characterized by bilateral ground-glass opacities and a stable clinical course.

Pathologic features of smoking-related lung diseases, with emphasis on smoking-related interstitial fibrosis and a consideration of differential diagnoses

Smoking-related interstitial fibrosis (SRIF) is frequently-seen and morphologically-distinctive finding in the lung tissue of cigarette smokers. It can be distinguished histologically from the idiopathic interstitial pneumonias and other causes of pulmonary interstitial fibrosis. SRIF is typified by dense thickening of the alveolar septa by thick collagen bundles with a hyalinized appearance, with the common admixture of bands of hyperplastic smooth muscle. Concomitant inflammation is minimal. SRIF predominates in the subpleural and centrilobular parenchyma, and is usually accompanied by the changes of centrilobular emphysema and respiratory bronchiolitis. Most patients with SRIF do not have clinical symptoms of the condition. This article reviews the pathologic features of SRIF and compares them with the appearances of other interstitial lung diseases, some of which are also related to cigarette smoking. Acute eosinophilic pneumonia is another lung disease that has an association with smoking, and its clinicopathologic features are considered here as well.

Clinical-Radiologic-Pathologic Correlation of Smoking-Related Diffuse Parenchymal Lung Disease

The direct toxicity of cigarette smoke and the body's subsequent response to this lung injury leads to a wide array of pathologic manifestations and disease states that lead to both reversible and irreversible injury to the large airways, small airways, alveolar walls, and alveolar spaces. These include emphysema, bronchitis, bronchiolitis, acute eosinophilic pneumonia, pulmonary Langerhans cell histiocytosis, respiratory bronchiolitis, desquamative interstitial pneumonia, and pulmonary fibrosis. Although these various forms of injury have different pathologic and imaging manifestations, they are all part of the spectrum of smoking-related diffuse parenchymal lung disease.

Respiratory bronchiolitis and lung carcinoma

BACKGROUND

Cigarette smoking is the primary causative factor for lung carcinoma and respiratory bronchiolitis (RB), particularly RB-associated interstitial lung disease (RB-ILD). However, the link between lung cancer and RB/RB-ILD remains undefined. We examined whether pathological fibrosis lesions exist simultaneously in patients with lung carcinoma because the fibrous lesions could be precancerous.

METHODS

Clinical, radiological, and pathological features were consecutively evaluated in 67 current smokers, 22 ex-smokers, and 35 nonsmokers who underwent surgical resection for lung carcinoma. The presence of interstitial changes was evaluated by high-resolution computed tomography (HRCT). The pathological examination focused on RB, RB with fibrosis, and coexistent interstitial changes.

RESULTS

RB with fibrosis was observed in 13/67 current smokers with centrilobular nodular and/or patchy ground-glass opacities patterns or emphysema on HRCT. RB without fibrosis was observed in 12/67 current smokers with a centrilobular pattern, emphysema, or a normal pattern on HRCT. The Brinkman smoking index was significantly higher in the RB with fibrosis group (1278±133) than in the RB without fibrosis group (791±131). No RB with/without fibrosis features were noted in nonsmokers or ex-smokers. Squamous cell carcinoma was observed in 11/13 patients with RB with fibrosis, whereas adenocarcinoma was observed in 7/12 patients with RB without fibrosis.

CONCLUSIONS

Squamous cell carcinoma located in peripheral areas was primarily observed in patients with RB with fibrosis, whereas adenocarcinoma was primarily observed in patients with RB without fibrosis. Interstitial fibrosis with RB caused by continuous heavy cigarette smoking may increase the risk of developing squamous cell carcinoma.