Background Chronic 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.

Methods In 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.

Results The 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).

Conclusion Persistent 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.

The authors have declared no competing interest.

NCT05302232

ZRL (Doctoral Fellowship, NIHR301674) is funded by the National Institute for Health Research (NIHR) for this research project. The views expressed in this publication are those of the author(s) and not necessarily those of the NIHR, NHS or the UK Department of Health and Social Care. FD and LST acknowledge funding from the Wellcome Trust (collaborative award reference 224257/Z/21/Z).

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Yorkshire & The Humber-Sheffield research ethics committee (REC reference 22/YH/0051) granted, Bromley research ethics committee and the Health Research Authority (REC 21/LO/0712) granted.

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