A substantial proportion of PSP patients suffer from recurrence. In the relevant literature, there are reports of up to 50% recurrence after first events, mainly appearing within two to 24 months [4, 20]. Surgical interventions are often recommended for prevention [12], especially in cases in which bullae or blebs have been demonstrated on chest CT [27]. As a potential prevention, surgery may differ from the other therapeutic modalities that include observation, oxygen therapy, air aspiration, and catheter or chest tube insertion. These other modalities we describe as conservative management
However, the protective effect of surgery has remained a controversial issue [8, 20, 28]. Previous studies have reported that surgery could be a risk factor for recurrence, not improving prognosis [14, 28, 29]. The recurrence rates in the young population who underwent surgery tended to increase [14]. In our study, with a few exceptions, PSP patients with surgical intervention experienced increased risk over those who had not been treated surgically. Only male patients aged ≥ 20 years showed no statistical significance between conservative and surgical management.
Notably, patients under 14 had a large discrepancy in recurrence rates between conventional and surgical treatment groups, regardless of gender. The overall 5-year recurrence rates were significantly higher in the ≥ 14 years, and < 20 years categories, and those of Group I showed similar trends. In Group II patients, those under 14 showed up to a 50% recurrence rate, nearly double that of other age categories.
A recent Korean study showed that the plateau of the pubertal growth spurt was at 14 years in girls and at 16 in boys [25, 30]. The maximal growth velocity has tended to be faster [25]; therefore, 14 would be a better cutoff for Korean children to distinguish ages in volumetric growth from maturation periods. Age under 20 could suggest late physical maturation and end of adolescence. We assumed that patients under the growth spurt age were likely to be more susceptible than in maturation periods.
Several investigations have suggested that younger age, lower BMI, and delayed puberty could be risk factors for recurrence, and these findings are consistent with the results of this study [4, 8, 20]. Lower BMI was often observed in children prior to the pubertal growth spurt; children experienced increases in height earlier than weight gain. Delayed puberty was related to a postponed growth spurt because the acceleration of skeletal growth velocity was observed in the early stage of puberty [22]. In male patients aged ≤ 20, the recurrence rate was not significantly different. This finding was consistent with our hypothesis.
Our study revealed that the recurrence rates of female patients were significantly lower than those of males in all age categories (Fig. 8A, B and C). These findings were quite different from previous studies that showed that the recurrence rates of females were significantly higher or had no association with gender. Female pneumothorax is related to gender-specific pulmonary abnormalities such as lymphangioleiomyomatosis or catamenial syndrome [4, 28, 31]. The exclusion of combined lung disease patients could have influenced our results.
The recurrence rate of a patient under the age of 14 who underwent conservative management was not statistically different between genders, but male patients who underwent surgical management showed higher recurrence rates (Fig. 8D and G). This could suggest that developing lung parenchyma of a male experiencing a pubertal growth spurt tends to be more susceptible to mechanical damage. There are reported inconsistencies between growth in chest wall dimension and height increase in males, not in females [32]. Male growth is significantly greater, and male growth velocity is significantly faster [22]. This seemingly should be related to delayed maturation of the lung surface, resulting in fragility; however, no direct evidence of this has been reported [32]. Surgical intervention showed no statistically significant influence on recurrences between gender after adolescent periods in our study, and this could be indirect evidence for an inverse relationship between rapid growth and pleural strength.
Our study had several limitations. First, the reason for surgical intervention for enrolled patients was not clear. Usually, surgery could be recommended when the lung has not been expanded over 7 days, large bullae are noted, or there is a recurrence [5, 8, 20]. In our study, the surgery seemed to have occurred after the first PSP event. Although we tried to exclude secondary pneumothorax cases, other reasons needed for surgical intervention may remain. The results of our study were possibly derived from the imbalance of enrolled patients. The lack of information relating with radiologic or pathologic findings essential for treatment strategies could cause severe skewedness in study materials, and therefore lead to inevitable restriction in data interpretation of our study.
Second, precocious characteristics such as height, weight, BMI, annual growth velocity, or family history can affect the recurrence rate [4, 15, 29, 31]. We could not identify anthropometric variables, which can be related to recurrence. Finally, conventional treatment comprised a broad spectrum of therapeutic options, from simple observation to large bore chest tube insertion in this study. This lack of homogeneity among treatments could critically affect recurrence, but our results did not reflect these factors. Further evaluation for each treatment modality using a large patient population is necessary.
Limitations could be related to a lack of understanding of the air leak mechanism details. Although the presence of ELCs, bullae or blebs, could justify early surgical intervention for the prevention of recurrences [12], the traditional concept as being main sources for occurrence makes this doubtful [8, 28]. Notable pathologic lesions have not been reported in certain patients [18], and the collateral ventilation system among pulmonary lobes has not been fully comprehended [28].
Our study showed significant association between higher recurrence rates and surgical intervention in young PSP patients who did not complete their physical growth (children, preadolescence and adolescence). This does not guarantee that that surgery is a negative prognostic factor for recurrence because of significant possibility in data skewedness, however, increasing interest in less invasive treatment strategies for primary spontaneous pneumothorax [23, 33, 34], serials of various conservative management could be considered before determination of surgery.