Intra-articular Injection of Lidocaine in Inflammatory Arthritis

Overview

To assess the contributions of peripheral neurons to joint pain, the investigators plan to ask patients to rate the pain in their chosen joint before and after an injection of local anaesthetic (lidocaine) and steroid into their joint. Lidocaine blocks voltage gated sodium channels (VGSCs) leading to a reversible block of action potential propagation in peripheral nerves. If the pain intensity reduces significantly following lidocaine injection, it suggests that the patients' pain is due to peripheral sensitization, and that this is dampened by the local anaesthetic. If the pain intensity does not change or only falls slightly, then other centrally mediated factors are contributing to pain. Before the investigators can use this method, the investigators need to ensure that reductions in pain score following joint injection are not due to placebo effect. Therefore, as part of this validation study patients will be randomised to receive either lidocaine plus steroid or, as a control, just steroid injection. The steroid is the main part of therapy as it relieves inflammation over a prolonged period, but is slower acting than lidocaine, and should not have an effect within ten minutes. Any improvement in ranking of pain within 10 minutes by patients receiving just steroid will therefore be due to placebo effect. The investigators hypothesis is that there will be a significant difference in change in pain score before and after injection between the study group (lidocaine plus steroid) and control group (0.9% saline plus steroid). This will confirm the absence of a significant placebo effect and mean the differences in change in pain scores seen in the study group are due to differences in pain processing

Patients will be randomised to receive joint injection of either lidocaine plus steroid or, as a control, just steroid injection. Pain scores (visual analogue score 0-10) in the chosen joint will be collected prior to injection and at 3, 5 and 10 minutes post injection. Pain scores will then again be collected at 1 month and 3 months to determine whether lidocaine reduced peripheral pain long term. Intra-articular joint injection with steroids is a frequent procedure in usual care and the investigators will only perform this test when a joint injection +/- aspiration is clinically indicated. Use of lidocaine in addition to steroid injection varies between rheumatologists, with 50% of Guys' and St Thomas' Hospital rheumatologists routinely using lidocaine and steroid, and others giving steroid alone. Therefore, all patients will still receive the same intervention they would if they were not taking part in the study, the only difference is measurement of pain scores before and after. In addition to collection of pain scores, the investigators will collect patient demographics and painDETECT questionnaire, a screening questionnaire which has been validated to identify neuropathic elements of pain in patients with IA. The investigators hypothesis is that there will be a significant difference in change in pain score before and after injection between the study group (lidocaine plus steroid) and control group (0.9% saline plus steroid). This will confirm the absence of a significant placebo effect and mean the differences in change in pain scores seen in the study group are due to differences in pain processing.