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

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 ( = 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 ( = 0.49, <0.001) but no association with age ( = -0.05,  = 0.680). There were also positive associations in EMH among cats with different BCSs ( = 0.001) and SMAs (thoracic spine,  = 0.021; lumbar spine,  = 0.014), but breed ( = 0.429) and sex ( = 0.187) had no effect. Finally, there was no change in EMH measurements in the paired samples ( = 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.