Axial spondyloarthritis is a chronic inflammatory disease affecting the spine, sacroiliac joints, entheses, and sometimes peripheral joints with a close link to HLAB27. Typical features include inflammatory back pain, limited spinal mobility, and sacroiliitis. The term axial spondyloarthritis (AxSpA) includes both Ankylosing Spondylitis (AS) where sacroiliitis is diagnosed by X-rays, and non-radiographic AxSpA, where sacroiliitis is diagnosed via magnetic resonance imaging (MRI).

Osteoporosis is common in AS patients, and sarcopenia may also develop due to inflammation and immobilization. Osteosarcopenia, the co-occurrence of osteoporosis and sarcopenia, might have an impact on morbidity and mortality of AxSpA patients.

This cross-sectional study aims to determine the frequency of osteosarcopenia in AxSpA patients and to investigate its relationship with various demographic and clinical factors. A control group with similar age and gender distribution will be recruited to evaluate osteosarcopenia. Our hypothesis is that osteosarcopenia will be more frequent in the AxSpA group compared to the control group. The study will also identify the demographic and clinical factors associated with osteosarcopenia in AxSpa.

Ankylosing Spondylitis (AS) is a chronic inflammatory disease of unknown etiology that affects the spine, sacroiliac joints, entheses regions, and sometimes peripheral joints. Its typical findings include inflammatory back pain, limited spinal mobility, and radiographic sacroiliitis. The term axial spondyloarthritis (AxSpA) describes a chronic inflammatory disease affecting the axial skeleton, including the spine and sacroiliac joints. It encompasses both patients with definite AS diagnosis with radiographic (X-ray) sacroiliitis, and patients with non-radiographic AxSpA whose sacroiliitis detected by MRI. Osteoporosis is among the clinical findings of AS. Similarly, sarcopenia may develop in AS patients due to both inflammation and immobilization. Osteosarcopenia is a clinical syndrome that includes both osteoporosis and sarcopenia. Osteosarcopenia may be a significant cause of morbidity and mortality in AxSpA patients.

This study aims to determine the frequency of osteosarcopenia in patients with AxSpA and to investigate its relationship with demographic and various clinical parameters. To determine the presence of osteoporosis, bone mineral density (BMD) measurement will be performed using Dual-energy X-ray absorptiometry (DXA). WHO definition for the diagnosis of osteoporosis will be used. A T score at or below -2.5 at the lumbal and/or hip region is defined as osteoporosis. Subsequently, to determine the presence of sarcopenia, patients will be assessed according to the European Working Group on Sarcopenia in Older People (EWGSOP2) algorithm through measurements of muscle strength, muscle mass quantity or quality, and physical performance. Skeletal muscle mass or quality will be measured by appendicular skeletal muscle mass (ASM) using both DXA, and bioelectrical impedance analysis (BIA). Skeletal muscle strength will be measured by grip strength and physical performance by gait speed. EWGSOP2 cut-off points will be used for low muscle strength (grip strength), low muscle quantity (ASM/height2) and low physical performance (gait speed). Then the sarcopenia diagnosis (probable, confirmed, severe) will be made according to the 2018 operational definition of sarcopenia by EWGSOP2. A healthy control group with similar age and gender distribution will be recruited to evaluate osteosarcopenia and compare with the patient group. After determining the presence of osteosarcopenia in AxSpA, the relationship between osteosarcopenia (sarcopenia and osteoporosis) and demographic/clinical parameters including age, gender, physical activity, disease duration, medications used (biological vs. non-biological), disease activity, spinal mobility, radiological involvement, and functional status will be investigated.

There has been no prior study on investigating osteosarcopenia in AxSpA. We expect a higher frequency osteosarcopenia in the AxSpA group compared to the control group. Additionally, the relationship between osteosarcopenia and clinical parameters will be demonstrated, thus increasing the attention and awareness of patients at high risk for developing osteosarcopenia, and facilitating early steps in treatment.

Inclusion Criteria:

Patient group:

• Participants with a diagnosis of AxSpA: Participants with diagnosis of Ankylosing Spondylitis according to the modified New York criteria and participants with diagnosis of non-radiographic Spondyloarthritis (SpA) according to the Assessment of SpondyloArthritis International Society (ASAS) 2009 criteria.
• Aged 18-65 years
• Who gave consent to participate in the study

Healthy control group:

• Age- and gender-matched healthy participants (age 18-65)
• Who gave consent to participate in the study

Exclusion Criteria:

1. Systemic high-dose steroid use (>5mg/day of prednisone for more than 3 months)
2. Possible other causes of secondary sarcopenia (uncontrolled diabetes, chronic heart failure, thyroid/parathyroid disease, chronic renal failure, chronic liver failure)
3. Hand-related disorders/diseases that could affect the healthy assessment of grip strength
4. Use of any medication that could potentially affect the bone metabolism (bisphosphonates, teriparatide, anticonvulsants, heparin, and anticoagulants)
5. Psoriasis, inflammatory bowel disease
6. Infection in the thigh area where ultrasonographic evaluation will be performed
7. Body weight over 100 kg (contraindication to be positioned in the BMD device)
8. Presence of malnutrition (individuals scoring 11 or below on the Mini Nutritional Assessment-Short Form (MNA))

The study will include participants with AxSpA aged 18-65 years who are being followed at the Department of Physical Medicine and Rehabilitation and the Division of Rheumatology at Ankara University Faculty of Medicine.

Age- and gender-matched healthy participants for control group will also be included. Control group will be selected from the relatives of outpatients or inpatients visiting the same clinic and from the hospital staff.

Before the study, all participants will be asked to read the study protocol and provide written informed consent to participate in the study.