Incidence of Primary Spontaneous Pneumothorax: a Validated, Register-Based Nationwide Study

Objectives The incidence of primary spontaneous pneumothorax is partly unknown. Commonly quoted estimates were published decades ago and recent large-scale epidemiological publications lack validation. We validated the pneumothorax diagnosis in a national registry and estimated the incidence of primary spontaneous pneumothorax in young patients. Methods Complete data on patients with an assigned pneumothorax diagnosis was retrieved from the National Danish Patient Registry. Initially, we validated the diagnosis in a selected population: all patient charts with an assigned pneumothorax diagnosis from one cardiothoracic department over a 25-year period (1984–2008) were reviewed. Subsequently, the national incidence of primary spontaneous pneumothorax in young, healthy individuals was estimated by restricting our population to patients ≤40 years of age admitted during a 5-year period (2009–2014). We performed a systematic read-though of patient charts in 50% of the complete national cohort to ensure that we only included patients with their first episode of primary spontaneous pneumothorax. Results Validation revealed a poor inter-rater agreement (κ=0.08). Therefore, we abstained from further analysis on directly retrieved data from the national database. Subsequently, a systematic re-evaluation of 7022 patients revealed an incidence rate of 12.3 cases per 100 000 (95% CI 11.5–13.1) in males and 2.2 cases per 100 000 (95% CI 1.9–2.6) in females (male/female ratio 5.9). Compared with the general Danish population, pneumothorax patients had a lower body mass index (p<0.001) and smoked more than the Danish population in general (p<0.001). Conclusions The incidence of primary spontaneous pneumothorax in a validated national study was lower than previously reported.