Ultrasonographic monitoring of feline epaxial muscle height as part of an annual wellness examination to assess for the development of sarcopenia

Abstract

Objectives: The aim of this study was to determine if epaxial muscle height (EMH) could be reliably incorporated into annual routine wellness screenings, and also determine its relationship to age, body condition score (BCS), subjective muscle assessment (SMA), breed and sex in mature cats.

Methods: EMH was determined independently by three observers from ultrasonographic examinations - collected by an additional trained individual - of cats enrolled at the Feline Healthy Ageing Clinic, University of Liverpool, UK. Age, body weight, BCS and SMA data were also collected.

Results: A total of 92 cats were included, 35 of which had repeat ultrasonographic examinations 12 months apart. Enrolled cats were a median age of 8 years and 9 months at the time of the first measurement. Variation in the quality of ultrasonographic images collected did not affect muscle depth measurements (P = 0.974). Further, there was good intra- and inter-observer repeatability for all observations (intraclass correlation range 0.97-0.99). There was a moderate positive association between EMH and body weight (r = 0.49, P <0.001) but no association with age (r = -0.05, P = 0.680). There were also positive associations in EMH among cats with different BCSs (P = 0.001) and SMAs (thoracic spine, P = 0.021; lumbar spine, P = 0.014), but breed (P = 0.429) and sex (P = 0.187) had no effect. Finally, there was no change in EMH measurements in the paired samples (P = 0.145) or correlation between percentage weight and EMH change over 12 months.

Conclusions and relevance: The accuracy of EMH measurement using ultrasonographic imaging is good, irrespective of observer experience and provided that the ultrasonographer has some training. This suggests that ultrasonographic measurement of EMH could have a major practical impact as a non-invasive determination of muscle mass in pet cat populations. Further research is required to assess longitudinal changes in muscle mass over time in senior pet cats.

Keywords: Mature; muscle condition; muscle measurement; sarcopenia.

Figure 1

Measurement of epaxial muscle height in mature cats using ultrasonography. A cursor was placed ventromedial to the muscle, at the interface between the 13th rib or vertebrae and the muscle. A second cursor was placed dorsolateral, at the interface between the subcutaneous fat and the muscle. Red ‘+’ are cursors and the yellow line represents a distance measurement (mm)

Figure 2

Bland–Altman plots showed inter-observer agreement in epaxial muscle height (EMH) measurements was excellent, with no evidence of systematic or proportional bias. (a) Inter-observer agreement between observer 1 (veterinarian) and observer 2 (veterinary student) on measurements from 92 mature cats. (b) Inter-observer agreement between observer 2 (veterinary student) and observer 3 (EBVS European specialist in veterinary diagnostic imaging) on 30 measurements from 30 mature cats. (c) Inter-observer agreement between observer 1 (veterinarian) and observer 3 (EBVS European specialist in veterinary diagnostic imaging) on 30 measurements from 30 mature cats. Individual measurements are shown by black filled circles, the solid black line represents the mean difference between observers (bias) and the red dotted lines show the 95% limits of agreement

Figure 3

Box and whisker plots depicting the coefficient of variation (CV) of epaxial muscle height measurements from 92 cats, taken by (a) observer 1 and (b) observer 2, and subdivided by image quality, graded from 1 (best) to 3 (worst) quality. The thick horizontal lines depict the median, the boxes depict the interquartile range and the whiskers represent the 95% range, with outliers being depicted as filled circles. Variability in muscle height measurements did not differ between cine-loops of different quality. (a) P = 0.961; (b) P = 0.546

Figure 4

Associations between mean feline epaxial muscle height (EMH) measurements and (a) age or (b) body weight in 92 mature cats. Individual measurements are shown by black filled circles, the black line represents the line of best fit and the grey shaded region represents the 95% confidence interval. There was a moderate positive correlation between EMH measurements and body weight but not age

Figure 5

Epaxial muscle height (EMH) measurements (mm) in 92 mature cats, stratified by body condition score (BCS). The thick horizontal lines depict the median, the boxes depict the interquartile range, the whiskers represent the 95% confidence interval and outliers are depicted as filled circles. Cats with a BCS of 8/9 had an EMH significantly greater than the EMH of cats with a BCS of 4/9 (P = 0.001), 5/9 (P = 0.001) or 6/9 (P <0.001). Cats with a BCS of 7/9 had an EMH significantly greater than the EMH of cats with a BCS of 4/9 (P = 0.048) and 6/9 (P = 0.012). *P = 0.01−0.05; **P = 0.001−0.01; ****P <0.001

Figure 6

Epaxial muscle height (EMH) measurements (mm) in 92 mature cats, stratified by subjective muscle assessment (SMA) and assessed over both the (a) thoracic and (b) lumbar spine. The thick horizontal lines depict the median, the boxes depict the interquartile range, the whiskers represent the 95% confidence interval and outliers are depicted as filled circles. Cats with normal muscle mass were assigned an SMA score if A (blue), while those with mild muscle wasting were assigned a score of B (yellow). At both sites, mean muscle height measurements were less in cats with SMA B than in those with SMA A (P = 0.021 and P = 0.014, respectively). *P = 0.01−0.05

Figure 7

Comparison of mean epaxial muscle height (mm) measurements in 35 cats, 12 months apart. The thick horizontal lines depict the median, the boxes depict the interquartile range and the whiskers represent the 95% confidence interval. Visit 1 denotes the initial measurement; visit 2 denotes the repeat measurement taken 12 months later. There was no change in muscle height over 12 months (P = 0.15)

Figure 8

Associations between percentage change in feline epaxial muscle height (EMH) measurements and percentage change in body weight over 12 months in 35 mature cats. Individual measurements are shown by black filled circles, the dark blue line represents the line of best fit and the grey shaded region represents the 95% confidence interval. There was no correlation between percentage change in EMH measurements and percentage change in body weight