Introduction:
Sarcopenia is the pathological reduction of skeletal muscle mass and strength. This condition is often underestimated in clinical practice, particularly in connective tissue diseases. The purpose of this study is to evaluate the prevalence of low muscle mass in primary Sjögren’s syndrome (pSS) and to explore the relationships linking muscles and bone tissue.

Material and methods:
Twenty-eight postmenopausal pSS patients were matched with 30 healthy controls and their body composition analysis was performed by dual-energy X-ray absorptiometry to investigate for sarcopenia considering appendicular lean mass (ALM) and the skeletal muscle mass index (SMI) as references. Bone mineral density analysis of lumbar spine (L1–L4), whole femur, femoral neck and whole body was also performed. Linear regression was used to assess the relationship between body composition and bone mineralization.

Results:
Low muscle mass was significantly higher in the pSS group compared to controls whether expressed as ALM, SMI [odds ratio (OR) = 18.40, confidence interval (CI): 4.84–72.08, p < 0.0001] or considering total body lean masses. Lean masses appeared to be the best estimators of bone mineralization: total lean body mass (TLBM) lumbar spine R2 = 0.72, p < 0.0001; TLBM femoral neck R2 = 0.36, p < 0.004; lean mass of upper limbs lumbar spine R2 = 0.70, p < 0.0001; femoral neck R2 = 0.66; lean mass of lower limbs lumbar spine R2 = 0.66, p < 0.0001; femoral neck R2 = 0.44, p = 0.008). Primary Sjögren’s syndrome patients had a significantly higher android/gynoid fat ratio compared to controls.

Conclusions:
Female pSS patients have lower muscle mass compared to healthy controls and are exposed to a higher risk of developing sarcopenia than healthy subjects. Our research demonstrates that the amount of lean tissue is the main predictor of bone mineralization in pSS.