The Impact of Body Mass Index on Disease Progression in Ankylosing Spondylitis

Obesity can be a factor that affects the course of chronic systemic inflammatory arthritis. The objective of this study was to characterise patients with ankylosing spondylitis (AS) according to an evaluation of their body mass index (BMI) and by exploring the link between the overweightness and obesity with routinely measured disease-specific variables, including disease activity (Bath Ankylosing Spondylitis Disease Activity Index BASDAI; Ankylosing Spondylitis Disease Activity Score, using CRP, ASDAScrp), spinal mobility (Bath Ankylosing Spondylitis Metrology Index, BASMI), functional capacity (BASFI), extraspinal manifestations like fatigue, uveitis, and peripheral arthritis present during the course of the disease. A total of 107 patients were included in the cross-sectional study fulfilling the modified New York criteria for AS. Patients were divided into three groups: with the evaluation of BMI ≤ 24.9, 25.0–29.9 (overweight) and ≥ 30.0 (obesity). The mean BMI was 25.13 (SD 4.07). 33% of patients were overweight and 15% were obese. The mean values of age, duration of AS, ASDAScrp, BASDAI, Bath Ankylosing Spondylitis Functional Index (BASFI), BASMI, pain in spine, and fatigue in the group with BMI ≤ 24.9 were lower than in the other groups (p < 0.05). There was no difference between groups in age of AS onset, uveitis and peripheral arthritis. AS patients who were overweight or obese had a higher level of the disease activity, pain, fatigue, functional disability and spinal mobility impairment with worse values in the case of obesity.