Background Pain in rheumatoid arthritis (RA) is typically regarded as related to on-going synovial inflammation in peripheral joints. However, in a subgroup of patients evidence indicates that pain can become an entity of its own caused by central sensitization (CS), elicited by but in time not directly related to ongoing inflammation. The painDETECT questionnaire (PDQ) was developed to differentiate neuropathic pain from unclear and non-neuropathic pain. In several studies it has been used to indicate CS owing to similarities in somatosensory profiles. Magnetic resonance imaging (MRI) can be used as an objective inflammation marker, quantified by the RA MRI Score (RAMRIS).
Objectives To evaluate the prognostic value of a PDQ score >18 on DAS28 response in RA patients taking a possible interaction with inflammation defined by RAMRIS synovitis scores into account.
Methods RA patients were included when they were to: 1) initiate a disease modifying antirheumatic drug (DMARD) or 2) initiate or switch a biological agent. At baseline and after 4 month of follow up patients went through an examination program incl. standard demographics, clinical examination, hand MRI, patient reported outcomes (incl. PDQ), and blood samples. Least-Squares Mean change (95% CI) was calculated using ANCOVA adjusting for the value at baseline. Multivariable regressions with DAS28 or RAMRIS synovitis change as outcome were performed to determine the prognostic variables. The model included PDQ-category, RAMRIS synovitis score and their interaction. Possible confounders were: gender, disease duration, baseline DAS28, and initiation group. PDQ score was interpreted as: >18 indication of CS, 13–18 unclear pain mechanism, <13 nociceptive pain. Pain classification consistency was explored.
Results 102 patients were included, 75 had an MRI scan performed. Mean changes stratified by PDQ-group are presented in the table showing the greatest changes in the CS-group (>18). Only baseline DAS28 was a significant predictor of DAS28 change (P<0.001) with a β-estimate (95%CI) of -0.65 (-88;-0.41). Baseline DAS28 and RAMRIS synovitis were significant predictors of RAMRIS synovitis change (P=0.01, P=0.02) with β-estimates of -0.67 (-1.17;-0.17) and -0.19 (-0.35;-0.03). Among the 12 patients with indication of CS (>18) at baseline all had changed classification-group at follow-up (8 to nociceptive pain and 4 to unclear).
Conclusions In this pragmatically sampled population of RA patients, pain classification by PDQ at treatment initiation had no prognostic value with regard to change in DAS28 or RAMRIS synovitis. In contrast, all patients classified with indication of CS by PDQ at baseline changed classification group and were even to gain most from treatment start in net changes. This might indicate that in RA, CS reflects normal neuroplasticity that is reversible with reduction of inflammation.
Koroschetz J, et al. Fibromyalgia and neuropathic pain-differences and similarities. A comparison of 3057 patients with diabetic painful neuropathy and fibromyalgia. BMC Neurol 2011;11:55
Disclosure of Interest None declared