To compare imaging findings on thoracic computed tomography (CT) examination in patients with primary spontaneous pneumothorax (SP), depending on their tobacco and/or cannabis consumption.

A total of 83 patients who had thoracic CT for primary SP were prospectively included. There were 65 men and 18 women with a median age of 33 years (IQR: 27; 44 years). The patients were further categorized into three groups according to their smoking habits. Thirteen patients were non-smokers, 38 were tobacco only smokers and 32 were tobacco and cannabis smokers. CT examinations were retrospectively reviewed for the presence of blebs, centrilobular and paraseptal emphysema and lung nodules in each group for comparison.

Emphysema was detected in 43/85 patients (51.8%), including 1/13 patients (7.7%) in the non-smoking group, 19/38 patients (50%) in the tobacco only group and 23/32 patients (71.9%) in the tobacco and cannabis smokers, with no difference between tobacco only and tobacco and cannabis smokers. No differences in type and location of emphysema was found between tobacco only and tobacco and cannabis smokers. Tobacco and cannabis smokers with emphysema were significantly younger than tobacco only smokers with emphysema (35 vs. 46 years, respectively) (P=0.009).

The prevalence of emphysema visible on CT is not different between tobacco and tobacco/cannabis smokers, however, it occurs at a younger age in tobacco and cannabis smokers. This result suggests that cannabis, when added to tobacco, may lead to emphysema at a younger age.