Clinically occult interstitial fibrosis in smokers: classification and significance of a surprisingly common finding in lobectomy specimens

This study reports the presence of surprisingly frequent and often severe interstitial fibrosis in cigarette smokers with no clinical evidence of interstitial lung disease. Twenty-three lobectomy specimens excised for neoplasms, including 20 from smokers, were extensively sampled, and examined semi-quantitatively for interstitial fibrosis, fibroblast foci, peribronchiolar metaplasia, honey-comb change, emphysema, and respiratory bronchiolitis. Interstitial fibrosis involving greater than 25% of slides was identified in 12 of 20 smokers (60%), but in none of the three never-smokers. Three cases were classified as specific forms of interstitial lung disease, including one each of usual interstitial pneumonia, Langerhans cell histiocytosis, and asbestosis. The remaining 9 cases did not fit with a named interstitial lung disease and were considered to represent examples of smoking-related interstitial fibrosis. This lesion was characterized by varying degrees of alveolar septal widening by collagen deposition along with emphysema and respiratory bronchiolitis. The fibrosis occurred both in subpleural and in deeper parenchyma. It surrounded enlarged airspaces of emphysema, but it also involved non-emphysematous parenchyma. Clinical progression was not documented in any case, although follow-up was short. These observations highlight the spectrum of unexpected fibrosis that is frequently encountered in lobectomy specimens from cigarette smokers. Additional investigation will be required to determine the clinical significance of smoking-related interstitial fibrosis and its relationship, if any, to other smoking-related diseases. It is important, however, that smoking-related interstitial fibrosis be distinguished from specific forms of fibrosing lung disease that may be associated with poor prognoses, especially usual interstitial pneumonia.