Prevalence of sarcopenia in adult patients with ankylosing spondylitis

Ankylosing Spondylitis is a chronic, progressive inflammatory rheumatic disease that involves primarily the sacroiliac joints and the axial skeleton. Sarcopenia is characterized by progressive and generalized loss of skeletal muscle mass and strength with a risk of adverse outcomes such as physical disability and poor quality of life. The study aimed to assess the prevalence of sarcopenia in patients with ankylosing spondylitis. A case-control study was conducted at Rheumatology Unit from January 2019 to July 2019. The study population consisted of 50 Iraqi patients diagnosed with AS and 50 healthy control. Demographic data, physical activity using General Practice Physical Activity Questionnaire (GPPAQ), disease activity scores using Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) were recorded. Sarcopenia assessment was done by using a dual-energy x-ray absorptiometry scan for body composition analysis and measuring skeletal mass index (SMI). The maximal voluntary grip strength of the hand was measured with an electronic dynamometer. Physical function was assessed by a 4-meter usual gait speed test. The prevalence of presarcopenia was 6% in both studied groups, while sarcopenia was 10% in AS patients. The mean value of BMI is significantly lower in patients with sarcopenia than in those without (p=0.001). The vast majority of the sarcopenic group (80%) were physically inactive which was statistically significant compared with the non-sarcopenic group (p=0.033). No significant association of treatment with anti-TNF or its duration was found between sarcopenia and non-sarcopenia groups (p=0.377; p=0.187). Both LM and handgrip showed fair validity to differentiate between AS patients and controls. Patients with AS are at higher risk of developing early sarcopenia than in healthy controls. Lower BMI and longer disease duration increase the risk of sarcopenia, while differences in gender, smoking and the use of anti-TNF do not influence the risk. Physical activity may improve muscle strength and perhaps decrease the risk.