© 2006 American Thoracic Society
Computed Tomography: A New Gold Standard for the Clinical Assessment of EmphysemaTo the Editor:
We read with particular interest the recent paper by Martinez and colleagues (1) that emphasized the value of computed tomographic (CT) densitometry in predicting mortality in subjects with severe emphysema. The authors indicate that they were surprised to find that the extent of emphysema in the lower lung zone was associated with reduced survival, whereas no association could be demonstrated for the overall percentage of emphysema. These data are contrasted with the findings of a study published by our group in which CT densitometry was found to be the best predictor of mortality in subjects with The high-resolution CT (HRCT) images that we utilized for densitometry were single slices obtained at the level of the inferior pulmonary veins and the aortic arch, representing the lower and upper lung, respectively (3). Consequently, we were not able to assess the overall percentage of emphysema, although we have subsequently demonstrated that single-slice analyses do correlate well with whole lung densitometry (lower zone, r = 0.928, p < 0.001; upper zone, r = 0.781, p < 0.001; n = 121). In contrast with the findings of Martinez and colleagues, we demonstrated that the severity of emphysema in the upper zones was the best predictor of mortality in subjects with AATD phenotype (PiZ). Our interpretation of this finding was that the natural history of emphysema progression in such patients was most commonly one of increasing apical extension from initial basal disease. As a consequence, the measurement of emphysema in the upper lung regions probably identified patients with either more extensive emphysema, or a phenotype more susceptible to severe disease. Our findings do differ from those of Martinez and coworkers, but we believe that this contrast reflects the inverse pattern of emphysema distribution and progression that is most commonly seen in these two patient groups. The distribution of emphysema is, consequently, predictive of mortality in both groups of patients. This finding is of importance in routine clinical practice for the assessment of prognosis, but may also be of great importance in patient selection for therapeutic trials. The heterogeneous distribution of emphysema seen between individuals and the differential value of regional densitometry indicates that detailed characterization of subjects is advisable before enrollment in clinical trials that employ CT densitometry as an outcome measure of emphysema progression. The study by Martinez and colleagues provides further evidence that CT densitometry is a valid measure of emphysema and indicates the need for further longitudinal studies to clarify whether emphysema distribution reflects differential genetic risk and outcome.
University Hospitals of Coventry and Warwickshire Coventry, United Kingdom
University Hospital Birmingham Birmingham, United Kingdom FOOTNOTES Conflict of Interest Statement: D.G.P. has received financial support from Boehringer Ingelheim and Altana for attendance at international conferences. His salary for research activity was supported by a noncommercial grant from Bayer Biologicals between 2001 and 2004 and he has received remuneration for consultancy work from Talecris. P.A.D. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. R.A.S. is involved as an Advisory Board member sporadically for several pharmaceutical companies (GlaxoSmithKline, Schering, Merck Sharp & Dohme) and lectures on behalf of Talecris, AstraZeneca (AZ), and Roche. He receives grant support (noncommercial) from Talecris and AZ and has accepted sponsorship to meetings from Boehringer ($5,000 for 2004, 2005, 2006). REFERENCES
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