Relapse of Ankylosing Spondylitis Patients Withdrawal Etanercept After Clinical Remission: a Following-up Study

Patients were followed up 6 weeks by telephone. The sample size was at least 30 people. If symptoms suggestive of relapse or other problems occurred, patients were invited to come back to the center. Relapse after etanercept withdrawal was defined as an increase Bath Spondylitis Disease Activity Index(BASDAI) score goes back to 80 percentages of it at the beginning of the trial16. The following data were collected: demographic and disease characteristics, therapeutic modification, clinical values (BASFI, Bath Ankylosing Spondylitis Global Score (BAS-G)), Ankylosing Spondylitis Disease Activity Score (ASDAS) and biologic values at baseline of the trial and the time of relapse. Adverse events and other safety measures were also collected.

Demographic and baseline disease characteristics were summarized with descriptive statistics and analysed with one-way ANOVA for continuous for continuous variables and χ2 tests for categorical variables. The Kaplan-Meier method was used to estimate the time-to-relapse rate after etanercept withdrawal. Time-to-relapse curves were compared between the group of patients received 12-week and 6-week treatment of etanercept through log-rank test. The influence of the following variables including age，duration of disease, onset age, BASDAI, ASDAS-CRP, C reaction protein(CRP), and erythrocyte sedimentation rate(ESR) was examined using the Cox proportional hazards model to evaluate at etanercept withdrawal on time-to-relapse. Every continuous variable was divided into 3 categories at approximately the 33% and 67% at first19. If the relative relapse rates were not significantly different in 2 contiguous categories, they were gathered together. If no clear difference was observed in 3 categories, the median was used as a cut-off point. Normal value such as 6 mg/L for CRP level were tested. The proportional hazards model was used to study the effect of each factor on time-to-relapse and identify the independent prognostic factors. Relapse rates are presented as estimate with standard error (SE), follow-up times as median (interquartile range), and hazard ratio as estimate with 95% confidence interval.

All analyses were performed using SPSS software v16.0 (SPSS, Inc, Chicago, IL).