David Lynch

MD

National Jewish Medical and Research Center

Professor of Radiology

NLST (Learn more about this study)

2005-90027

Nov 2, 2006

Prevalence of Interstitial Lung Disease in NLST Population

Purpose/ Background: Interstitial lung disease is an umbrella term that includes more than 130 chronic lung disorders. In these conditions, there is infiltration of the interstitium of the lungs by varying amounts of inflammation and fibrosis, usually resulting in progressive physiologic impairment. ILD may be classified into several groups including idiopathic interstitial pneumonias, interstitial pneumonias with known causes such as collagen vascular disease, drug reactions, occupational/environmental exposures such as asbestos and chronic hypersensitivity pneumonitis, sarcoidosis, and other forms of diffuse lung parenchymal diseases. Although classification and diagnosis of ILDs are now well-established, the prevalence of ILDs is still uncertain, and there is no population-based prevalence study using CT in large population. The five-year survival rate for patients with ILD is variable depending on the pattern of disease. The subgroup with a usual interstitial pneumonia (UIP) pattern has a 5-yr survival of only 20%, whereas the subgroups with desquamative interstitial pneumonia (DIP) or nonspecific interstitial pneumonia (NSIP) have a better response to treatment and a much better outcome (1). Unfortunately, it appears that many of the reported cases of UIP are in patients who present late in the course of their disease. Thus, with increasing interest in specific treatments for each ILD, it would be useful to have an accurate estimate of prevalence, particularly of those with early or subclinical disease. Despite considerable progress in the diagnosis and classification of the ILDs, only a few reports of the prevalence of ILDs have been published. In the most comprehensive population-based report, the prevalence of ILD was found to be 0.81% in males and 0.67% in female (3). However this report was based on the clinical records; there was no recorded review of CT scans, and only 7% of patients underwent surgical biopsy. In an autopsy-based study, the prevalence of pre-clinical ILD was estimated at 1.8% (3). These studies pre-dated the currently accepted classification of interstitial lung diseases. CT scanning is quite accurate for characterization of the pattern of disease, particularly UIP. In several series, a correct first choice diagnosis is made by computed tomography in 75-90% of patients with various major ILDs, including sarcoidosis, silicosis, IPF, lymphangitis carcinomatosis, and Langerhans cell histiocytosis (4). CT has been shown to be a sensitive method for detection of diffuse lung disease in a variety of contexts, including subjects with asbestos exposure, collagen vascular disease, and hypersensitivity pneumonitis. In a study of healthy volunteers, Mastora et al detected parenchymal ground glass abnormality on CT in 47 (33%) of 144 cigarette smokers. However, the extent and clinical significance of this abnormality was not documented. We are unaware of any other CT-based screening study for detection of interstitial lung disease in a general population. National Lung Screening Trial (NLST) is a large cancer screening trial sponsored by the National Cancer Institute (NCI) to compare two methods of detecting lung cancer in healthy older current and former smokers (55-74 years of age). The main purpose of this trial is to determine which screening test, spiral computed tomography (CT) or standard chest X-ray will be better at reducing lung cancer deaths. Imaging studies are obtained at baseline (T0) and annually for 2 years (T1 and T2; 3 studies per participant)) In February 2004, NCI reached its goal of recruiting 50,000 participants across all sites in a 16 month period. At UCHSC we were able to recruit and screen 3743 participants, 1846 of whom were randomized to receive chest CT as a screening procedure, and 1897 were randomized to chest radiographs. The third round of annual screening in these subjects is almost complete. These patients will be followed for mortality for up to eight years. The purposes of our study are to determine the prevalence of ILDs by CT in the NLST population, and to determine the rate of progression of CT-detected ILD on sequential examinations. Additionally, although the number of patients is anticipated to be relatively low, we plan to perform exploratory analysis to determine the relationship between occupational and environmental exposures and the presence of ILD, and to determine the mortality in this group of patients compared with a control group.