Background/Purpose:

Sarcopenia, or age-related loss of muscle mass, is well documented in the general population and is associated with functional limitation and increased mortality. Literature on sarcopenia in axial spondyloarthritis (axSpA) is sparse and therefore the extent of the problem is virtually unknown. The aim of this study is to determine the prevalence of sarcopenia in patients with axSpA and determine associations with severity of disease.

Methods:

Forty-three consecutive patients (79.1% male, 97.7% Caucasian) with axSpA were included. Demographic data, spinal metrology, anthropometric measures, serum markers and patient-reported outcome measures were collected. Body composition analysis was performed using bioelectrical impedance analysis (BIA): fat mass, fat-free mass and predicted skeletal muscle mass were collected. Height was measured to the nearest 0.1 cm. Skeletal muscle mass index (SMI) was calculated by appendicular skeletal muscle mass (sum of predicted muscle mass in all 4 limbs) divided by height squared. Sarcopenia was defined as per the European Working Group on Sarcopenia in Older People definition as SMI ≤ 8.87 kg/m² in men and ≤ 6.42 kg/m² in women. BMI was categorised as normal if <25kg/m², overweight if >25kg/m² and obese if >30kg/m². SPSS was used for statistical analysis.

Results:

Baseline characteristics are outlined in table 1, along with significant differences between genders. Mean BMI is 28.8kg/m²(SD 6.3). A high BMI is present in 72.1% of the cohort: 27.9% have normal weight, 37.2% are overweight and 34.9% are obese. Sarcopenia is present in 41.9% (n=18) of the cohort (50% of men and 11.1% of women). In the males with sarcopenia compared to those without, BMI (24 v 34.1 kg/m²,p<0.01), waist circumference (88.9 v 105.1 cm,p=0.01), hip circumference (95.6 v 109.9 cm,p<0.01) and fat percentage (20% v 30%,p<0.01) are significantly lower. Testosterone is significantly higher in patients with sarcopenia (18.5 v 13.8,p<0.05). There is no significant difference in disease activity parameters, although there is a trend towards lower BASMI in patients with sarcopenia (3.7 v 4.8,p=0.09). There is no significant difference in number of co-morbidities between patients with and without sarcopenia.

Only 58.8% of men with sarcopenia have normal weight. The remaining 41.2% are overweight. No men with sarcopenia are obese, but all men with normal weight are sarcopenic.

Conclusion:

Almost 42% of this axSpA cohort has sarcopenia. There is no association with disease outcome measures. Of the sarcopenic patients, just under half are overweight, which is at odds with our usual perception of sarcopenia. Physicians need to consider sarcopenia in axSpA, even in patients with high BMI.

Table 1: Baseline and anthropometric characteristics of cohort, along with significant differences between genders.