Background Limited data are available on the influence of gender and lifestyle factors, such as smoking, alcohol consumption and Body Mass Index (BMI) on disease activity and response to TNF inhibitors (TNFi) in ankylosing spondylitis (AS).

Objectives This study aimed to determine whether these factors influence age at diagnosis, disease activity and response to TNFi.

Methods In a prospective study, clinical data (age, gender, C-reactive protein, Ankylosing Spondylitis Disease Activity Score (ASDAS), Bath Ankylosing Spondylitis Disease Activity Score (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI) and Bath Ankylosing Spondylitis Metrology Index (BASMI), smoking, alcohol consumption and BMI) were collected in AS patients from a observational cohort, who started or switched treatment with TNFi. Data were collected at baseline and after 6, 12 and 24 months. Independent T-tests and linear regression analyses were performed to assess the influence of gender and lifestyle factors on age at diagnosis and disease activity.

Results In total, 312 consecutive AS patients, 34% female, were included with a mean follow-up of 18.9 months. Most patients (172, 55%) showed significant improvement after start of TNFi of whom 86 patients (28%) had a clinically important (ASDAS decrease >1.1) and 86 (26.9%) a major clinical improvement (ASDAS decrease >2.2). BMI was significantly correlated with age at diagnosis (p=0.016; 95% CI: 0.07 – 0.65): an increase of BMI with three points delayed the AS diagnosis with one year. At baseline, smoking and gender were not correlated with the ASDAS, but BASDAI and BASMI were both inversely related to BMI. Male gender was significantly associated with a higher chance at clinical response (improvement of the BASDAI with 50% or a 2 point decrease) to TNFi (p=0.041). At one year follow-up the clinical improvement of males versus females was respectively 62% vs. 43% and at two year follow-up 59% vs. 46%. Males also showed a significantly higher ASDAS improvement after one year of follow-up compared to females (p=0.015).

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Conclusions Significantly less females had a clinical response compared to males after one and two years of TNFi treatment. A higher BMI not only prolonged the time to AS diagnosis up to one year, but also negatively influenced the BASDAI and BASMI scores. Female gender and high body weight should be taken into consideration when the efficacy of TNFi is assessed, by stratifying for these factors in the analysis.

Disclosure of Interest None declared