The pathogenesis of subpleural bleb formation in patients with a spontaneous pneumothorax is poorly defined. In an attempt to define the causal mechanisms of bleb formation, we studied the pathology in a cohort of young smokers with a pneumothorax.
We examined clinical records and pathology specimens from a consecutive series of 12 patients with a history of cigarette smoking who presented with a spontaneous pneumothorax. All failed conservative therapy with tube thoracostomy and underwent thoracoscopic bleb resection with mechanical pleurodesis and/or partial pleurectomy.
The patients (8 males and 4 females) ranged in age from 20 to 30 years (mean 21.3). There were 8 Caucasians, 2 African-Americans, and 2 Asians. The Body Mass Index of the group ranged from 15.5 to 20.3 (mean 19.1). The patients had a smoking history of 1 to 16 pack-years (mean 6.9). The pulmonary pathology was remarkably similar in all the patients. In each case, there was pleural fibrosis with a sub-pleural chronic pneumonitis characterized by interstitial inflammation and fibrosis with collections of tar-laden macrophages in the airspaces. In 4 patients, sub-pleural emphysema was evident. The interstitial pneumonitis varied in severity and extended to a variable degree into the sub-pleural parenchyma. In 4 patients, the interstitial pneumonitis was present diffusely throughout the biopsied lung. The pathology here closely resembled that of desquamative interstitial pneumonitis.
There are young individuals with a thin body habitus and smoking history who present with a pneumothorax that is associated with a peripheral interstitial pneumonitis. It is proposed that the pathogenesis of smoking-associated pneumothorax begins with the accumulation of tar-laden macrophages that are toxic to the dependent lung parenchyma beneath the pleura. This pneumonitis and fibrosis in the context of the greater mean distending pressures associated with an asthenic body habitus result in the formation of subpleural blebs and consequent pneumothorax.
The proposed causal sequence between cigarette smoking and spontaneous pneumothorax should allow further focused efforts aimed at defining the specific mechanisms and thus permit targeted therapy.
S.R. Carr, None.