Accuracy of ultrasound, bioelectrical impedance analysis and anthropometry as point-of-care measurements of skeletal muscle mass in patients with inflammatory bowel disease

Background: Disturbance of skeletal muscle mass has clinically important implications in patients with inflammatory bowel disease (IBD), but accurate quantification requires radiation-intense techniques. Aims: We aimed to compare point-of-care muscle assessments and their change with therapy with those using reference-standard whole-body dual energy X-ray absorptiometry (DXA). Methods: Adult patients with IBD and healthy controls underwent prospective assessment of muscularity by ultrasound of the dominant arm and both thighs, bioelectrical impedance analysis (BIA), anthropometric measurements, and DXA. Patients with active IBD were assessed again ≥13 weeks after initiating biologic induction therapy. Results: In 54 patients with IBD and 30 controls, all muscle assessments correlated significantly with DXA-derived skeletal muscle index (SMI). In IBD, ultrasound of the arm and legs had the best agreement with DXA-derived SMI (mean difference 0 kg/m², 95% limits of agreement −1.3 to 1.3), while BIA overestimated DXA-derived SMI by 1.07 (−0.16 to +2.30) kg/m². In 17 patients who underwent biologic therapy, the percentage change in DXA-derived SMI correlated significantly with the percentage change in all other muscle assessment techniques. Responders (n = 9) increased SMI from baseline to follow-up when derived from DXA (mean 7.8–8.5 kg/m², p = 0.004), ultrasound of the arm and legs (300–343 cm², p = 0.021) and BIA (9.2–9.6 kg/m², p = 0.011). Conclusions: Ultrasound of the arm and legs out-performed other point-of-care methods in its accuracy of measuring muscle mass. All methods, except mid-arm circumference, were responsive to therapy-induced change. Ultrasound is the preferred non-invasive test for measuring muscle mass in patients with IBD.