The incidence and risk factors of asymptomatic primary spontaneous pneumothorax detected during health check-ups

BACKGROUND Patients with primary spontaneous pneumothorax (PSP) usually complain of sudden-onset dyspnea and pleuritic chest pain. However, asymptomatic PSP has been incidentally detected on chest X-rays. In this study, we analyzed the incidence, characteristics, risk factors, and prognosis of asymptomatic PSP detected during regular medical check-ups in university students. METHODS In this study, 101,709 chest X-rays were performed during medical check-ups for students at the University of Tokyo between April 2011 and March 2016. Among them, 43 cases of asymptomatic PSP (0.042%) were detected. We calculated the lung collapse rate of pneumothorax using Kircher's method. We also analyzed risk factors associated with asymptomatic PSP using characteristics inspected in medical check-ups. RESULTS The incidence of asymptomatic PSP was significantly higher in men than in women (0.050% vs 0.018%). Multivariate analysis revealed an association of younger age, greater height, lower body mass index, and greater height growth per year with an increased risk of asymptomatic PSP in male students. Mild lung collapse (<10%) was present in 22 of 43 students with asymptomatic PSP; among these, eight students eventually underwent an invasive therapy. CONCLUSIONS The prevalence of asymptomatic PSP among university students was as high as 0.042%. In addition to known risk factors for conventional PSP, greater height growth was a risk factor for asymptomatic PSP. Careful follow-up is very important because a considerable number of patients with mild lung collapse eventually require an invasive medical procedure.