Predictors of Responsiveness to Bisphosphonate Treatment in Patients with Complex Regional Pain Syndrome Type I: A Retrospective Chart Analysis.

Objective: The aim of this study was to assess whether the effectiveness of bisphosphonate infusion in patients with complex regional pain syndrome type I (CRPS-I) is influenced by variables related to patient and/or disease characteristics.

Methods: This is a retrospective analysis of patients referred in the last five years to our rheumatologic tertiary care center, all fulfilling the Budapest CRPS-I diagnostic criteria and treated with three different bisphosphonate schedules (clodronate, pamidronate, and neridronate). For every subject, demographic and clinical variables were retrieved and retrospectively analyzed. We identified variables that independently influenced the therapeutic outcome of patients by a logistic regression analysis. For exploratory purposes, the effectiveness of the different bisphosphonate treatments employed was compared.

Results: Among the 194 patients included in the analysis, the overall therapeutic response rate was 71.6%. Logistic regression analysis showed that the independent predictive variables for therapeutic effectiveness were disease duration (odds ratio [OR] = 0.83, 95% confidence interval [CI] = 0.72-0.96 for a one-month increment), fracture as a predisposing event (OR = 3.23, 95% CI = 1.29-8.03), and "warm" disease subtype (OR = 4.88, 95% CI = 1.57-15.20). These variables were found to influence the odds of responsiveness when analyzed together with age at onset, gender, and disease localization. No significant difference in therapeutic effectiveness was found by comparing the three different bisphosphonate schedules employed.

Conclusion: Early disease, fracture as a predisposing event, and "warm" disease subtype are predictors of responsiveness to bisphosphonate treatment in patients with CRPS-I.