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Birmingham, AL
Dr. Cerfolio is Associate Professor of Surgery, Chief of the Section of General Thoracic Surgery, Division of Cardiothoracic Surgery, University of Alabama at Birmingham.
Correspondence to: Robert James Cerfolio, MD, FCCP, Division of Cardiothoracic Surgery, University of Alabama at Birmingham, 1900 University Blvd THT 712, Birmingham, AL 35295; e-mail: Rcerfolio{at}uab.edu
Dr. Mieno and colleagues have presented a well-written and interesting article (see page 1960) concerning other potential benefits derived from lung volume reduction surgery (LVRS) besides improvement in dyspnea and pulmonary function test results. Prior to accepting the conclusion of any study, its methodology must be critically scrutinized and questioned.
The study by Mieno and colleagues is retrospective cohort study that spans a 4-year period. This lengthy time frame lends itself to treatment bias. It may introduce some biases since treatment strategies can change, but it is unlikely that many significant changes were made.
The exclusion criteria removed patients with "chronic therapy capable of interfering with bone metabolism," but we are not told what those therapies were, nor are we told what treatment or conditions were accepted. But the most obvious problem with this study is that it is not randomized. Seventy patients were offered LVRS, but only 40 underwent resection. The other 30 patients served as the retrospective control group. Are they really adequate control subjects? Isn’t selection bias possible? Perhaps their refusal to undergo surgery alone led to the observed differences in the two groups. Perhaps the actual performance of the LVRS had nothing to do with the increased bone mineral density (BMD) in the treated group, rather those that wanted surgery were more motivated, more physically active, or had a better mental outlook on their disease state. Perhaps they had some other quality linked to wanting to undergo a relatively risky operation that leads to improvement in health and BMD that we cannot measure. This study, like any other nonrandomized study, suffers from all the inherent problems of a retrospective study.
Another potential flaw is the effect that steroids have on BMD. The authors tried to account for this variable. They compared the 21 patients who continued to take some steroids after surgery to all 30 control patients, since none of them had their steroids completely discontinued. We are only told that these 30 patients had "a significant reduction in the median daily dosage." However, the quantification of that reduction is not given. It may have been useful from a statistically standpoint. For example, the amount of reduction and in how many patients could have led to a dose-response analysis. The authors report "significant improvements [in the 21 patients who underwent LVRS] compared to patients treated only with respiratory rehabilitation." But again this significant improvement is not quantified. In the "Discussion," we are told a dose-dependent analysis could not be done because of the low numbers. Do these low numbers, 21 in one group and 30 in the other, force us to question the other findings of the study? Each reader must decide this for themselves.
Despite the concerns mentioned above, this report is clinically important. The authors have acknowledged the limitations of the study and in so doing have strengthened their article. The fact that the patients who underwent LVRS had improvement not only in BMD but in so many other hormones and nutritional parameters lends more scientific support to the performance of this controversial operation. In properly selected patients and in an experienced center, LVRS is safe and effective. It leads to a lessening of dyspnea, improvement in quality of life, and perhaps to increased nutritional status and in BMD as well. The authors are to be congratulated for their outstanding results, hard work, and well-written study.
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