Introduction
Loss of skeletal muscle mass (SMM), one of the hallmarks in the diagnosis of sarcopenia, is a frequent condition in patients with inflammatory bowel disease (IBD) and it is a negative predictor of disability and poor clinical outcomes.1 Despite its clinical relevance, its diagnosis remains challenging due to limited access to standard methods like dual-energy X-ray absorptiometry (DEXA), computed tomography (CT), and magnetic resonance imaging (MRI). More practical alternative, such as bioelectrical impedance analysis (BIA) and ultrasound (US), should be investigated.2-4
Aims & Methods
This study aims to evaluate the feasibility, reproducibility, and diagnostic accuracy of US measurement of psoas muscle thickness compared to BIA in assessing SMM in IBD patients.
US psoas muscle thickness adjusted for body mass index (BMI) was compared with BIA-derived SMM normalized to squared height. Feasibility and reproducibility between the two investigators were evaluated by intra-class correlation coefficient (ICC). SMM normalized to squared height and US thickness adjusted for BMI values were compared with Pearson’s test. Results were considered significant with a p value <0.05. The diagnostic accuracy of US psoas muscle thickness measurement in comparison to SMM with BIA was assessed by calculating sensitivity (Sens), specificity (Spec), positive and negative likelihood ratios (LR+, LR-) with their 95% confidence intervals (95% CI). This study was approved by the local Ethics Committee (no. 0049113).
Results
A total of 86 consecutive patients with IBD were prospectively enrolled, including 67.4% with CD and 32.6% with UC. The cohort had a male predominance (68.6%), with a mean age of 50.4 ± 17 years and a mean BMI of 23.68 ± 3.73 kg/m². US assessment of psoas muscle thickness was feasible in all patients. Inter-operator reproducibility was excellent with an ICC of 0.951. A significant positive correlation (r = 0.54, p < 0.0001) was observed between the US-derived psoas thickness adjusted for BMI and SMM as measured by BIA and normalized to squared height. Receiver operating characteristic (ROC) curve analysis revealed an area under the curve (AUROC) of 0.753 for men and 0.758 for women. Sex-specific cut-offs of psoas thickness × BMI were determined (≤108.18 cm·kg/m² for men, ≤66.9 cm·kg/m² for women), yielding sensitivities of 93.5% and 78.5% and specificities of 53.6% and 69.2%, respectively. Low SMM was defined according to BIA-based thresholds normalized to height squared, with cut-offs of <6.68 kg/m² for females and <8.97 kg/m² for males, as proposed by Peine et al. 5
Table 1. Ultrasound psoas thickness compared to skeletal muscle mass values at bioelectrical impedance analysis
| Sens (%)
| Spec (%)
| AUROC | LR+ | LR- | Cut-off proposed* |
Men
| 93.5 | 53.6 | 0.753 | 2.01 | 0.12 | 108.18 |
| Women | 78.5 | 69.2 | 0.758 | 2.5 | 0.31 | 66.9 |
Note:*sonographic psoas thickness x body mass index
Conclusion
US measurement of psoas muscle thickness is a feasible, low-cost, non-invasive and reproducible method for evaluating SMM in IBD patients. It shows promising diagnostic accuracy compared to BIA and, since the psoas muscle is a key anatomical landmark for evaluating the terminal ileum, it could be used as a practical first-line screening tool for sarcopenia especially in routine bowel US. Further prospective studies are needed to refine cut-off values, validate findings in diverse populations, and assess the long-term prognostic implications of this technique within the framework of personalized IBD management.
References
1. Nishikawa, H. et al. Inflammatory bowel disease and sarcopenia: Its mechanism and clinical importance. Journal of Clinical Medicine vol. 10 Preprint at https://doi.org/10.3390/jcm10184214 (2021).
2. Oshima, Y., Shiga, T., Namba, H. & Kuno, S. Estimation of whole-body skeletal muscle mass by bioelectrical impedance analysis in the standing position. Obes Res Clin Pract 4, (2010).
3. Smith, R. L., Taylor, K. M., Friedman, A. B., Gibson, R. N. & Gibson, P. R. Systematic Review: Clinical Utility of Gastrointestinal Ultrasound in the Diagnosis, Assessment and Management of Patients with Ulcerative Colitis. Journal of Crohn’s and Colitis vol. 14 Preprint at https://doi.org/10.1093/ecco-jcc/jjz163 (2020).
4. Mulinacci, G. et al. P466 Ultrasound muscle assessment for sarcopenia screening in patients with Inflammatory Bowel Disease: A prospective study (SarcUS-IBD). J Crohns Colitis 18, (2024)
5. Peine, S. et al. Generation of normal ranges for measures of body composition in adults based on bioelectrical impedance analysis using the seca mBCA. Int J Body Compos Res 11, (2013).
Disclosure
No conflict of interest