Aberrant Analgesic Response to Medial Branch Blocks in Patients With Characteristics of Fibromyalgia

Background and Objectives: Facet interventions for spine pain have high failure rates, and preprocedural prediction of response is nearly impossible. A potential explanation may be aberrant central pain processing as that existing in conditions like fibromyalgia. To test this hypothesis, we conducted a retrospective study investigating the impact of having characteristics of fibromyalgia on the acute analgesic response to a first diagnostic medial branch block (MBB). Methods: We evaluated the analgesic responses of 187 patients that underwent MBB. Patients were categorized as "fibromyalgia-positive" or "fibromyalgia-negative" using the 2011 fibromyalgia survey criteria. Pre-procedural and postprocedural pain scores and patient-completed pain diaries up to 24 hours postprocedure were collected. A linear mixed model was used to study longitudinal effects of MBB on pain responses. Results: Fibromyalgia-positive patients had a worse preprocedural pain phenotype (ie, greater pain severity, higher levels of depressive and anxiety symptoms, reduced function). Binary categorization of fibromyalgia status was not associated with a difference in immediate postprocedural pain relief; however, the longitudinal analgesic response across time varied significantly between groups (P = 0.0005). Fibromyalgia-negative subjects showed the expected steep decline in pain scores, followed by gradual return to baseline, whereas a more aberrant pattern was noted in the fibromyalgia-positive group. Pain scores for fibromyalgia-negative patients were also lower by -1.07 (SE = 0.37) on average after theMBB (P = 0.005). Conclusions: Characteristics of fibromyalgia may indicate pain that is more centralized in nature, a factor that may explain the aberrant analgesic response to this peripheral intervention. This may have implications for future prediction of treatment response, although prospective studies are needed.