A randomised controlled trial of the effect of intra-articular lidocaine on pain scores in inflammatory arthritis

Abstract

AbstractBackgroundChronic pain in inflammatory arthritis (IA) reflects a complex interplay between active disease in a peripheral joint and central pro-nociceptive mechanisms. Since intra-articular lidocaine may be used to abolish joint-specific peripheral input to the central nervous system, we aimed to validate its use as a clinical tool to identify those IA patients whose pain likely incorporates centrally mediated mechanisms.MethodsIn this two-armed randomised placebo-controlled trial, IA patients requiring an intra-articular steroid injection were 1:1 randomised to additionally receive intra-articular lidocaine or control (0.9% saline). Pain numerical rating scale (NRS) scores were collected at baseline and 3, 5, and 10 minutes post injection. Between group differences in NRS scores at each post-randomisation assessment were estimated using linear mixed-models. Heterogeneity in lidocaine effect was evaluated by baseline painDETECT (grouped ‘high’ (>18) or ‘low’ (≤18)). Analysis in a second cohort validated the painDETECT analysis and included additional markers of centrally mediated pain.ResultsThe placebo effect of intra-articular injection was low. Post lidocaine injection, those in the high painDETECT group had an NRS score 2.2 points higher than those in the low painDETECT group (p=0.03). In the replication sample, post lidocaine NRS scores were significantly higher in those with a high painDETECT score, fibromyalgia, and low-pressure pain threshold at the trapezius (p=0.002, p=0.001, p=0.005 respectively).ConclusionPersistent high pain post intra-articular lidocaine injection could potentially be used as an indicator of pro-nociceptive mechanisms that are centrally mediated, informing centrally-targeted analgesic strategies.