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St. Antonius Hospital Nieuwegein, The Netherlands
Correspondence to: F. M. N. H. Schramel, MD, PhD, FCCP, Department of Pulmonary Diseases, St. Antonius Hospital, PO Box 2500, 3430 CM Nieuwegein, The Netherlands; e-mail: antolong{at}knmg.nl
To the Editor:
Sihoe et al (August 2000)1 described a study in which they tested the hypothesis that thoracic CT scanning could help to predict the probability of the occurrence of primary spontaneous pneumothorax (SP) by detecting lung bullae. Several studies have been performed concerning the possible relationship of blebs and/or bullae to the development of recurrent primary SP that do not confirm the conclusion of Sihoe et al.
Mitlehner et al2 analyzed 35 patients with primary SP who underwent thoracic CT scans. The presence of blebs and/or bullae had no predictive value for recurrences during follow-up. Smit et al3 studied 101 patients with first-time and recurrent SPs who underwent thoracic CT scans. In 12 patients, bilateral pneumothoraces occurred. The percentages of patients who had bullae among those with first-time SPs and recurrent SPs were not significantly different, nor was the percentage of bullae that occurred on the pneumothorax side significantly different compared to those occurring on the contralateral side. Janssen et al4 could not demonstrate differences in the presence of blebs and/or bullae during video-assisted thoracoscopy in patients with first-time or recurrent SPs.
In patients with COPD, bullae frequently can be detected. A study by Videm et al5 in 303 patients with primary and secondary SPs showed no significant relationship between the recurrence rate of SPs and COPD. Independent risk factors for recurrence in 122 patients with primary SPs were reported as follows: pulmonary fibrosis detected on chest radiographs; physical characteristics; smoking behavior; and age.6
From these findings, one can conclude that the presence of blebs and/or bullae in patients with primary SPs has no predictive value for the future development of recurrences. Therefore, investigations to diagnose blebs and/or bullae should not influence the choice of treatment to prevent future recurrences.7 Obviously, Sihoe et al1 did not review the literature as stated above and therefore performed a study with a noninteresting study objective.
Sihoe et al1
showed a significant difference in the
occurrence of contralateral SP between patients with or without
contralateral blebs and/or bullae (p = 0.04). Table 1
shows the data in a 2 x 2 manner. The Pearson
2 test was used. However, this test is only
applicable when cells of the 2 x 2 table contain a minimum
frequency, which was not the case in the study by Sihoe et
al.1
A zero value in one of the four cells invalidates the
test. The results of the test are therefore questionable and may be
biased. Other approaches to test for significance in a 2 x 2 table
(eg, Fisher’s Exact Test) did not show significance.
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References
Prince of Wales Hospital Hong Kong, China
Correspondence to: Anthony P. C. Yim, MD, FCCP, Professor and Chief, Division of Cardiothoracic Surgery, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, NT, Hong Kong SAR, China; e-mail: yimap{at}cuhk.edu.hk
To the Editor:
We thank Drs. Schramel and Zanen for their interest in our work. Many of the points they raised in their letter were almost identical to those of Dr. Marc Noppen1 . For the sake of space, we will not repeat ourselves and readers are asked to refer to our reply to Dr. Noppen’s letter, in which several issues were fully addressed.
We are well aware of the studies cited by Drs. Schramel and Zanen in their letter, but we disagree that they amount to definitive proof that bullae are of no predictive value for the recurrence of primary spontaneous pneumothorax (PSP). In the article by Mitlehner and colleagues,2 blebs or bullae could be found in 31 of 35 patients with PSP. On follow-up of 32 of the 35 patients for an average of 32 months, 8 patients (25%) had recurrences of PSP. Although there was no control group in this study, the recurrence rate was far higher than would have been expected from the general population. In an earlier article by Lesur and associates3 studying CT scan findings in patients with PSP vs healthy individuals matched for age, sex, and smoking habits, significantly more "emphysematous lesions" were found in the PSP group.
In the articles by Smit et al4 and Janssen et al5 (Dr. Schramel was a coauthor of both articles), which looked at CT scan and video-assisted thoracoscopic findings in patients with PSP, no differences in the bulla morphology could be found in patients with first-time vs recurrent PSP. The authors argued, therefore, that bullae have no bearing on PSP recurrence. However, this conclusion seemed to be based more on their opinion than on evidence. There were no control groups or follow-up data in either study. This would be analogous to a cross-sectional study with a small cohort of smokers in which smoking habits were analyzed. If no significant correlation could be found between the amount of smoking and the presence of lung cancer, it could be concluded that smoking was not a cause of cancer!
Until more knowledge on the pathogenesis of PSP becomes available, the exact relationship between bullae and PSP is likely to remain controversial. Scientific knowledge is built up from small additive increments, and it is important that we should keep an open mind on this subject and allow new evidence to speak for itself.
References
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