Time and predictors of response to tumour necrosis factor- blockers in psoriatic arthritis: an analysis of a longitudinal observational cohort

OBJECTIVE: To determine predictors and time to response to treatment with TNF-alpha blockers in patients with PsA in a longitudinal observational cohort. METHODS: We performed a cohort analysis of patients who were followed prospectively in a large PsA clinic. Response to treatment was defined as an improvement of at least 40% in active (tender and/or swollen) and swollen joint count (SJC) and 50% improvement in the Psoriasis Area and Severity Index (PASI) score. RESULTS: Ninety-five patients were included in the analysis. Of the total patients, 72.6 and 77.9% demonstrated 40% improvement in active joint counts at 3 and 12 months, respectively. Also, 80.5 and 87.4% of the patients showed 40% improvement in SJC at 3 and 12 months, respectively. A PASI50 was achieved by 54 and 60.4% after 3 and 12 months of treatment, respectively. Of 17 patients who did not achieve 40% improvement in total SJC at 3 months, 11 (64.7%) responded at 12 months. In multivariate analysis, the number of swollen joints at baseline predicted response of total active joints at 12 months [odds ratio (OR) 1.34; P = 0.02], whereas past use of TNF-alpha blocker decreased odds of response (OR 0.05; P = 0.01). CONCLUSION: TNF-alpha blockers are effective in most PsA patients with the majority responding within 3 months of treatment. A significant proportion of the early non-responders will have a delayed response to treatment. Higher SJC at baseline and no prior use of TNF-alpha blockers predict response.