Background/Purpose:

Obesity is a worldwide public health concern, due to its association with morbidity and mortality. Existing literature looking at obesity in axial spondyloarthropathy (axSpA) is sparse, but indicates increased BMI is prevalent. The impact of obesity on disease outcome is less well known. We aimed to determine the prevalence of obesity in a large axSpA cohort and describe its association with disease outcomes.

Methods:

Ankylosing Spondylitis Registry of Ireland (ASRI) provided the cohort for this study. The objectives of ASRI are to provide descriptive epidemiological data on the Irish axSpA population. A standardised clinical assessment is performed on each patient. Structured interviews provide patient-reported data. Weight is recorded in kilograms (kg) and height in centimetres (cm). BMI is categorised per the World Health Organisation criteria: normal weight <25 kg/m², overweight 25-29.9 kg/m² and obese ≥ 30 kg/m². Statistical analysis is performed using SPSS.

Results:

As of June 2017, 683 patients have been enrolled: 77% (n=526) male, mean age 45.9 ± 12.4 years, mean disease duration 19±12.2 years, mean delay to diagnosis 8.6±8.1 years, 78.8% fulfil modified New York criteria. Mean BASDAI is 3.9±2.5, BASMI is 3.6 ± 2.5, BASFI is 3.6± 2.7 and HAQ is 0.52 ±0.52.

Mean BMI in this cohort is 27.8±5.3 kg/m²: 1.1% (n=7) underweight, 31.6% (n=205) normal BMI, 38.9% (n=252) overweight, 28.4% (n=184) obese. Overall, 67.3% are overweight or obese: these patients are significantly older, have longer disease duration and more comorbidities, especially hypertension and hyperlipidaemia, than normal weight patients. Obese patients have significantly higher disease activity and worse physical function, spinal mobility and quality of life than both normal weight and overweight patients (table 1). The prevalence of smoking is lower in obese patients than normal weight patients. In univariable linear regression, BMI and obesity are associated with higher BASDAI, ASQoL, BASMI, BASFI and HAQ scores (table 2). In multivariable regression analysis, obesity remains an independent predictor of higher disease activity and worse function.

Conclusion:

Over two thirds of this axSpA cohort are overweight or obese. Higher BMI and obesity independently predicts worse disease outcomes. Strategies should be put in place to actively reduce axSpA patient’s BMI.

Table 1: Patient characteristics stratified according to BMI categories. Values are mean (±SD) or n (%).

*p value <0.05 compared to BMI <25 kg/m²; † p value <0.05 compared to BMI 25-30 kg/m².

Table 2: Linear regression analysis of association between BMI and obesity with clinical outcome.