508149
research-article2014
PENXXX10.1177/0148607113508149Journal of Parenteral and Enteral NutritionLetter to the Editor
Letters to the Editor
Could Single-Slice Quantitative Computerized Tomography Image Analysis at the Midpoint of the Third Lumbar Region Accurately Predict Total Body Skeletal Muscle?
We read with interest the brief report by Sheean et al,1 who reported the inability of the Subjective Global Assessment (SGA) to accurately detect sarcopenia in critically ill populations. SGA is a “gold standard” bedside assessment tool, but its predictive power among critically ill patients is limited.2,3 Although we agree on the limitations of SGA among critically ill patients, we also believe that the following methodological issues in current work are noteworthy. First, the study by Sheean et al1 measured muscle mass by single-slice quantitative computed tomography (CT) image analysis at the midpoint of the third lumbar (L3) region. Accuracy of the single-slice CT image was previously assessed by Shen et al,4 who compared this with the gold standard technique of magnetic resonance imaging. However, they used the fourth to fifth lumbar region for this analysis and did not report results on specific anatomic landmarks such as the second to third lumbar or third to fourth lumbar regions. Moreover, the study by Shen et al consisted only of healthy adults, so it was difficult to extrapolate these results for measurements at the L3 region among the critically ill population. Second, Sheean et al1 addressed the article by Mourtzakis et al5 on the validity of the technique in the current work. Mourtzakis et al compared single-slice quantitative CT image analysis at the L3 region with dual-energy x-ray absorptiometry assessment, which is not the gold standard. Validity assessment studies that use a reference instrument that is not a gold standard are open to misclassifications due to estimation errors of the reference standard. Therefore, before reaching definite conclusions, the influence of such a potential misclassification on the results should be assessed. Umut Safer, MD Department of Geriatrics, Gulhane School of Medicine, Ankara, Turkey Vildan Binay Safer, MD Department of Physical Medicine and Rehabilitation, Ankara Physical Medicine and Rehabilitation Research and Training Hospital, Ankara, Turkey
References 1. Sheean PM, Peterson SJ, Gomez Perez S, et al. The prevalence of sarcopenia in patients with respiratory failure classified as normally nourished using computed tomography and subjective global assessment
Journal of Parenteral and Enteral Nutrition Volume 38 Number 4 May 2014 415–416 © 2014 American Society for Parenteral and Enteral Nutrition DOI: 10.1177/0148607113508149 jpen.sagepub.com hosted at online.sagepub.com
[published online August 26, 2013]. JPEN J Parenter Enteral Nutr. doi:10.1177/0148607113500308. 2. Atalay BG, Yagmur C, Nursal TZ, et al. Use of subjective global assessment and clinical outcomes in critically ill geriatric patients receiving nutrition support. JPEN J Parenter Enteral Nutr. 2008;32(4):454-459. 3. Vermilyea S, Slicker J, El-Chammas K, et al. Subjective global nutritional assessment in critically ill children. JPEN J Parenter Enteral Nutr. 2013;37(5):659-666. 4. Shen W, Punyanitya M, Wang Z, et al. Total body skeletal muscle and adipose tissue volumes: estimation from a single abdominal cross-sectional image. J Appl Physiol. 2004;97(6):2333-2338. 5. Mourtzakis M, Prado CM, Lieffers JR, Reiman T, McCargar LJ, Baracos VE. A practical and precise approach to quantification of body composition in cancer patients using computed tomography images acquired during routine care. Appl Physiol Nutr Metab. 2008;33(5):997-1006.
Author Response DOI: 10.1177/0148607113508150
We appreciate the opportunity to respond to Drs Safer and Binay Safer regarding our recent publication on the correlations between sarcopenia assessed by computed tomography (CT) imaging and Subjective Global Assessment classifications of nutritional status. Their reservations and concerns surround the use of single-slice images at the third lumbar (L3) region and the validity of such methodologies in critically ill patients. The specificity and precision of CT- and magnetic resonance imaging (MRI)–based methods for body composition research have been extensively developed and validated by pioneers in the field of body composition.1,2 The authors are correct in that Shen et al3 used MRI to assess the accuracy of single abdominal images for extrapolations of total body estimates. However, this study also highlighted that the highest correlation between single-slice skeletal muscle (SM) area and total body SM volume was found 5 cm above the L4 to L5 level. Thus, this study supported future investigations using single-slice images at the L3 region for SM quantification. Subsequently, the L3 region has been used by numerous investigators employing CT methodologies in various patient populations to classify sarcopenia.4-7 These studies clearly show the reproducibility of this method and, furthermore, demonstrate its strong negative associations with adverse outcomes. Our study simply extends this approach, reflecting an opportunistic exploration in patients
Downloaded from pen.sagepub.com at The University of Iowa Libraries on June 18, 2015
416
Journal of Parenteral and Enteral Nutrition 38(4)
with critical illness. We objectively sited the many limitations to our study and agree that further validation work is needed in this population comparing single-slice images for whole-body extrapolation. Until these studies are completed, however, cross-sectional imaging provides reliable and objective measurements of muscle mass and remains one of the preferred methods to quantify SM. Patricia Sheean, PhD, RD Carol Braunschweig, PhD, RD University of Illinois at Chicago, Chicago, Illinois Sarah Peterson, MS, RD Rush University Medical Center, Chicago, IL
References 1. Heymsfield SB, Wang Z, Baumgartner RN, Ross R. Human body composition: advances in models and methods. Annu Rev Nutr. 1997;17:527-558.
2. Heymsfield S. Human Body Composition. 2nd ed. Champaign, IL: Human Kinetics; 2005. 3. Shen W, Punyanitya M, Wang Z, et al. Total body skeletal muscle and adipose tissue volumes: estimation from a single abdominal cross-sectional image. J Appl Physiol. 2004;97(6):2333-2338. 4. Antoun S, Baracos VE, Birdsell L, Escudier B, Sawyer MB. Low body mass index and sarcopenia associated with dose-limiting toxicity of sorafenib in patients with renal cell carcinoma. Ann Oncol. 2010;21(8): 1594-1598. 5. Lieffers JR, Bathe OF, Fassbender K, Winget M, Baracos VE. Sarcopenia is associated with postoperative infection and delayed recovery from colorectal cancer resection surgery. Br J Cancer. 2012; 107(6):931-936. 6. Prado CM, Baracos VE, McCargar LJ, et al. Sarcopenia as a determinant of chemotherapy toxicity and time to tumor progression in metastatic breast cancer patients receiving capecitabine treatment. Clin Cancer Res. 2009;15(8):2920-2926. 7. Tan BH, Birdsell LA, Martin L, Baracos VE, Fearon KC. Sarcopenia in an overweight or obese patient is an adverse prognostic factor in pancreatic cancer. Clin Cancer Res. 2009;15(22):6973-6979.
Downloaded from pen.sagepub.com at The University of Iowa Libraries on June 18, 2015
research-article2014
PENXXX10.1177/0148607113508149Journal of Parenteral and Enteral NutritionLetter to the Editor
Letters to the Editor
Could Single-Slice Quantitative Computerized Tomography Image Analysis at the Midpoint of the Third Lumbar Region Accurately Predict Total Body Skeletal Muscle?
We read with interest the brief report by Sheean et al,1 who reported the inability of the Subjective Global Assessment (SGA) to accurately detect sarcopenia in critically ill populations. SGA is a “gold standard” bedside assessment tool, but its predictive power among critically ill patients is limited.2,3 Although we agree on the limitations of SGA among critically ill patients, we also believe that the following methodological issues in current work are noteworthy. First, the study by Sheean et al1 measured muscle mass by single-slice quantitative computed tomography (CT) image analysis at the midpoint of the third lumbar (L3) region. Accuracy of the single-slice CT image was previously assessed by Shen et al,4 who compared this with the gold standard technique of magnetic resonance imaging. However, they used the fourth to fifth lumbar region for this analysis and did not report results on specific anatomic landmarks such as the second to third lumbar or third to fourth lumbar regions. Moreover, the study by Shen et al consisted only of healthy adults, so it was difficult to extrapolate these results for measurements at the L3 region among the critically ill population. Second, Sheean et al1 addressed the article by Mourtzakis et al5 on the validity of the technique in the current work. Mourtzakis et al compared single-slice quantitative CT image analysis at the L3 region with dual-energy x-ray absorptiometry assessment, which is not the gold standard. Validity assessment studies that use a reference instrument that is not a gold standard are open to misclassifications due to estimation errors of the reference standard. Therefore, before reaching definite conclusions, the influence of such a potential misclassification on the results should be assessed. Umut Safer, MD Department of Geriatrics, Gulhane School of Medicine, Ankara, Turkey Vildan Binay Safer, MD Department of Physical Medicine and Rehabilitation, Ankara Physical Medicine and Rehabilitation Research and Training Hospital, Ankara, Turkey
References 1. Sheean PM, Peterson SJ, Gomez Perez S, et al. The prevalence of sarcopenia in patients with respiratory failure classified as normally nourished using computed tomography and subjective global assessment
Journal of Parenteral and Enteral Nutrition Volume 38 Number 4 May 2014 415–416 © 2014 American Society for Parenteral and Enteral Nutrition DOI: 10.1177/0148607113508149 jpen.sagepub.com hosted at online.sagepub.com
[published online August 26, 2013]. JPEN J Parenter Enteral Nutr. doi:10.1177/0148607113500308. 2. Atalay BG, Yagmur C, Nursal TZ, et al. Use of subjective global assessment and clinical outcomes in critically ill geriatric patients receiving nutrition support. JPEN J Parenter Enteral Nutr. 2008;32(4):454-459. 3. Vermilyea S, Slicker J, El-Chammas K, et al. Subjective global nutritional assessment in critically ill children. JPEN J Parenter Enteral Nutr. 2013;37(5):659-666. 4. Shen W, Punyanitya M, Wang Z, et al. Total body skeletal muscle and adipose tissue volumes: estimation from a single abdominal cross-sectional image. J Appl Physiol. 2004;97(6):2333-2338. 5. Mourtzakis M, Prado CM, Lieffers JR, Reiman T, McCargar LJ, Baracos VE. A practical and precise approach to quantification of body composition in cancer patients using computed tomography images acquired during routine care. Appl Physiol Nutr Metab. 2008;33(5):997-1006.
Author Response DOI: 10.1177/0148607113508150
We appreciate the opportunity to respond to Drs Safer and Binay Safer regarding our recent publication on the correlations between sarcopenia assessed by computed tomography (CT) imaging and Subjective Global Assessment classifications of nutritional status. Their reservations and concerns surround the use of single-slice images at the third lumbar (L3) region and the validity of such methodologies in critically ill patients. The specificity and precision of CT- and magnetic resonance imaging (MRI)–based methods for body composition research have been extensively developed and validated by pioneers in the field of body composition.1,2 The authors are correct in that Shen et al3 used MRI to assess the accuracy of single abdominal images for extrapolations of total body estimates. However, this study also highlighted that the highest correlation between single-slice skeletal muscle (SM) area and total body SM volume was found 5 cm above the L4 to L5 level. Thus, this study supported future investigations using single-slice images at the L3 region for SM quantification. Subsequently, the L3 region has been used by numerous investigators employing CT methodologies in various patient populations to classify sarcopenia.4-7 These studies clearly show the reproducibility of this method and, furthermore, demonstrate its strong negative associations with adverse outcomes. Our study simply extends this approach, reflecting an opportunistic exploration in patients
Downloaded from pen.sagepub.com at The University of Iowa Libraries on June 18, 2015
416
Journal of Parenteral and Enteral Nutrition 38(4)
with critical illness. We objectively sited the many limitations to our study and agree that further validation work is needed in this population comparing single-slice images for whole-body extrapolation. Until these studies are completed, however, cross-sectional imaging provides reliable and objective measurements of muscle mass and remains one of the preferred methods to quantify SM. Patricia Sheean, PhD, RD Carol Braunschweig, PhD, RD University of Illinois at Chicago, Chicago, Illinois Sarah Peterson, MS, RD Rush University Medical Center, Chicago, IL
References 1. Heymsfield SB, Wang Z, Baumgartner RN, Ross R. Human body composition: advances in models and methods. Annu Rev Nutr. 1997;17:527-558.
2. Heymsfield S. Human Body Composition. 2nd ed. Champaign, IL: Human Kinetics; 2005. 3. Shen W, Punyanitya M, Wang Z, et al. Total body skeletal muscle and adipose tissue volumes: estimation from a single abdominal cross-sectional image. J Appl Physiol. 2004;97(6):2333-2338. 4. Antoun S, Baracos VE, Birdsell L, Escudier B, Sawyer MB. Low body mass index and sarcopenia associated with dose-limiting toxicity of sorafenib in patients with renal cell carcinoma. Ann Oncol. 2010;21(8): 1594-1598. 5. Lieffers JR, Bathe OF, Fassbender K, Winget M, Baracos VE. Sarcopenia is associated with postoperative infection and delayed recovery from colorectal cancer resection surgery. Br J Cancer. 2012; 107(6):931-936. 6. Prado CM, Baracos VE, McCargar LJ, et al. Sarcopenia as a determinant of chemotherapy toxicity and time to tumor progression in metastatic breast cancer patients receiving capecitabine treatment. Clin Cancer Res. 2009;15(8):2920-2926. 7. Tan BH, Birdsell LA, Martin L, Baracos VE, Fearon KC. Sarcopenia in an overweight or obese patient is an adverse prognostic factor in pancreatic cancer. Clin Cancer Res. 2009;15(22):6973-6979.
Downloaded from pen.sagepub.com at The University of Iowa Libraries on June 18, 2015
