Screening for sarcopenia and obesity by measuring thigh muscle and fat thickness by ultrasound in patients with rheumatoid arthritis

Abstract

Objectives: Sarcopenia is relatively common in rheumatoid arthritis (RA) patients. Thicknesses of the quadriceps muscle and fat are easily measured by ultrasound (US) and are known to be related to skeletal muscle mass and fat mass, respectively.

Methods: Eighty-four patients enrolled in the prospective correlation research of sarcopenia, skeletal muscle, and disease activity in rheumatoid arthritis study (UMIN000023744) underwent US examinations of anterior thigh muscle thickness (MT) and fat thickness (FT). Muscle and body fat (BF) mass were also examined by a body composition analyzer. Whether MT and FT were related to sarcopenia and obesity was examined.

Results: MT was significantly lower in RA patients with sarcopenia than in those without (23.8 vs 28.2 mm, P = 0.001). MT was related to sarcopenia (men: r = 0.56, P = 0.02, women: r = 0.32, P = 0.01). The cut-off value of MT for sarcopenia was 24.7 mm in men and 19.7 mm in women on receiver operating characteristic curve analyses. FT was correlated with BF percentage (%BF; men: r = 0.66, P < 0.01, women: r = 0.62, P < 0.001), which was estimated by 2.04xFT+8.53 in men and 1.2xFT+17.42 in women by a simple linear regression model. This means that FT ≥ 8.1 mm in men and FT ≥ 14.6 mm in women indicated obesity.

Conclusions: US examination of the anterior thigh was useful to detect sarcopenia and obesity in RA patients.

Keywords: Obesity; Prospective observational study; Rheumatoid arthritis; Sarcopenia; Ultrasound.

Fig. 1

The ultrasound machine is always ready to measure muscle and fat thicknesses in the consultation room. The ultrasound probe is set at the midpoint between the upper edges of the patella and greater trochanter (a). The muscle and fat thicknesses are evaluated in a transverse image (b). Muscle thickness (MT) is defined as the distance between the anterior fascia of the rectus femoris muscle (RF) and the posterior fascia of the vastus intermedius muscle (VI). Fat thickness (FT) is defined as the distance between the anterior and posterior subcutaneous fat.

Fig. 2

Receiver operating characteristic (ROC) curve analysis of muscle thickness (MT) in relation to sarcopenia. The area under the ROC curve (AUC) for MT is 0.825 in men (a) and 0.745 in women (b).

Fig. 3

A simple linear regression model between body fat percentage (%BF) and fat thickness (FT). The plot indicates patients, separately for men (a) and women (b). FT ≥ 8.1 mm in men (a) and FT ≥ 14.6 mm (b) in women indicate obesity.