Outcome prediction following sympathetic block for complex regional pain syndrome

Evidence for the efficacy of sympathetic blocks as either diagnostic or therapeutic tools in complex regional pain syndrome (CRPS) remains anecdotal. Systematic evaluation has been confounded by inconsistent terminology, difficulties in objectively quantifying physical findings, and failure to control for co-morbid psychological factors. This study examines the relative contribution of physical and psychometric features as prospective predictors of outcome following sympathetic block in the treatment of CRPS. Twenty patients with CRPS characterized by mechanical allodynia and vasomotor/sudomotor disturbance were treated with sympathetic blocks. Long-term outcome was assessed at > 6 months following the last treatment using a mailed questionnaire. Pain relief and functional improvement were negatively influenced by anxiety (P < 0.001). When the improvement in the initial visual analog for pain (VAS) was 50% or greater following "diagnostic" sympathetic block, the percent improvement was highly correlated with improvement at long-term follow-up (P < 0.001). Higher "sensitivity" scores on the Neuropathic Pain Scale (P < 0.001), C fiber allodynia (P < 0.01) and Adelta-fiber allodynia (P < 0.01) on quantitative sensory testing, and pretreatment reported dynamic mechanical allodynia (P < 0.02) all predicted positive response to initial sympathetic block. While sympathetic blocks can be helpful in the reduction of mechanical allodynia, and thus the facilitation of physical and occupational therapy, ultimate response to a regime that includes medications is not predicted by sympathetic block alone.