Bilateral Anterior Thigh Thickness: A New Diagnostic Tool for the Identification of Low Muscle Mass?

Objectives: To develop an ultrasonographic scanning protocol that included an assessment of muscle size [the proposed Bilateral Anterior Thigh Thickness (BATT)] and quality (echogenicity) to support the diagnosis of sarcopenia in a clinical setting. To determine the relationship of BATT and ultrasound echogenicity with physical function parameters of sarcopenia and test the reliability of ultrasound echogenicity measurements.

Design: Observational study.

Setting and participants: The BATT criteria were determined from a reference population of 113 healthy younger adults and tested in 39 healthy older adults and 31 frail older adults.

Methods: Ultrasonography was used to measure the thickness of rectus femoris and vastus intermedius bilaterally; the thickness measurements were summed to calculate the BATT. Diagnostic criteria for low muscle size were calculated from the reference population. Echogenicity was assessed using freeze-frame images. All individuals underwent anthropological, frailty, and physical performance assessments.

Results: The mean (standard deviation) BATTs for the subsamples were as follows: healthy young women (n = 54), 60.6 mm (±11.1); healthy young men (n = 59), 75.8 mm (±10.71); healthy older women (n = 27), 38.4 mm (±7.18); healthy older men (n = 13), 47.5 mm (±10.8); frail older women (n = 17), 29.2 mm (±11.4); and frail older men (n = 14), 27.3 mm (±13.9). The calculated cutoffs for low muscle size in older adults using the BATT criteria were 38.5 mm in women and 54.4 mm in men in this population. The BATT was correlated with grip strength (ρ = 0.750, P < .001 for women; ρ = 0.619, P < .001 for men) and walk speed (ρ = -0.599, P < .001 for women; ρ = -0.324, P = .003 for men). Ultrasound echogenicity increased with age and frailty. Lay sonographers were able to reliably reproduce the same muscle thickness measurements but not the same muscle echogenicity measurements.

Conclusions/implications: The data support the use of ultrasonography to identify low muscle size in sarcopenia. Ultrasonography provides a pragmatic diagnostic tool that is noninvasive, without radiation exposure, and usable in both community and hospital settings. The proposed BATT criteria could be used to identify low muscle size in clinical practice and research, and in this study have excellent correlation with physical parameters of muscle health. However, this now needs testing in a validation cohort. Ultrasound echogenicity has been demonstrated to be an important surrogate marker of muscle health, but difficulties with reproducibility preclude its widespread clinical use.