Single-slice CT measurements allow for accurate assessment of sarcopenia and body composition

Emerging evidence on body composition suggests that sarcopenic obesity (obesity with depleted muscle mass) might be predictive of morbidity and mortality in non-malignant disease and also of toxicity to chemotherapy. We aimed to assess the prevalence and clinical implications of sarcopenic obesity in patients with cancer. Between Jan 13, 2004, and Jan 19, 2007, 2115 patients with solid tumours of the respiratory or gastrointestinal tract from a cancer treatment centre serving northern Alberta, Canada, were identified. Available lumbar CT images of the obese patients were analysed for total skeletal muscle cross-sectional area; these values were also used to estimate total body fat-free mass (FFM). Of the 2115 patients initially identified, 325 (15%) were classified as obese (body-mass index [BMI] > or =30). Of these obese patients, 250 had CT images that met the criteria for analysis. The remaining 75 patients were recorded as without assessable scans. Obese patients had a wide range of muscle mass. Sex-specific cut-offs that defined a significant association between low muscle mass with mortality were ascertained by optimum stratification analysis: 38 (15%) of 250 patients who had assessable CT images that met the criteria for analysis were below these cut-offs and were classified as having sarcopenia. Sarcopenic obesity was associated with poorer functional status compared with obese patients who did not have sarcopenia (p=0.009), and was an independent predictor of survival (hazard ratio [HR] 4.2 [95% CI 2.4-7.2], p<0.0001). Estimated FFM showed a poor association with body-surface area (r(2)=0.37). Assuming that FFM represents the volume of distribution of many cytotoxic chemotherapy drugs, we estimated that individual variation in FFM could account for up to three-times variation in effective volume of distribution for chemotherapy administered per unit body-surface area, in this population. This study provides evidence of the great variability of body composition in patients with cancer and links body composition, especially sarcopenic obesity, to clinical implications such as functional status, survival, and potentially, chemotherapy toxicity.

A single abdominal cross-sectional computerized axial tomography and magnetic resonance image is often obtained in studies examining adipose tissue (AT) distribution. An abdominal image might also provide additional useful information on total body skeletal muscle (SM) and AT volumes with related physiological insights. We therefore investigated the relationships between abdominal SM and AT areas from single images and total body component volumes in a large and diverse sample of healthy adult subjects. Total body SM and AT volumes were derived by whole body multislice magnetic resonance imaging in 123 men [age (mean +/- SD) of 41.6 +/- 15.8 yr; body mass index of 25.9 +/- 3.4 kg/m(2)] and 205 women (age of 47.8 +/- 18.7 yr; body mass index of 26.7 +/- 5.6 kg/m(2)). Single abdominal SM and AT slice areas were highly correlated with total body SM (r = 0.71-0.92; r = 0.90 at L(4)-L(5) intervertebral space) and AT (r = 0.84-0.96; r = 0.94 at L(4)-L(5) intervertebral space) volumes, respectively. R(2) increased by only 5.7-6.1% for SM and 2.7-4.4% for AT with the inclusion of subject sex, age, ethnicity, scanning position, body mass index, and waist circumference in the model. The developed SM and AT models were validated in an additional 49 subjects. To achieve equivalent power to a study measuring total body SM or AT volumes, a study using a single abdominal image would require 17-24% more subjects for SM and 6-12% more subjects for AT. Measurement of a single abdominal image can thus provide estimates of total body SM and AT for group studies of healthy adults.