Objective We compare the effect of HAS, a-tDCS on the left dorsolateral prefrontal cortex (l-DLPFC), and rest-testing on pain measures [(cold pressor test (CPT) (primary outcome) and heat pain threshold]. We also compare their effects on the motor evoked potential (MEP) (primary outcome), short intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP). Methods This randomized, blind, crossover trial included 18 women with fibromyalgia, aged from 18 to 65 years old. They received at random and in a crossover order a-tDCS over the l-DLPFC (2mA), HAS, or a rest-testing. Results HAS compared to a-tDCS increased the pain tolerance with a moderate effect size (ES) [Cohen’s f=−0.78; (CI 95%; −1.48 to −0.12)]. While compared to rest-testing, HAS increased the CPT with a large ES [Cohen’s f=−0.87; (CI 95%; −1.84 to −0.09)]. The a-tDCS compared to HAS increased the MEP amplitude with large ES [Cohen’s f=−1.73 (CI 95%; −2.17 to −0.17)]. Likewise, its ES compared to rest-testing in the MEP size was large [Cohen’s f=−1.03; (CI 95%; −2.06 to −0.08)]. Conclusion These findings revealed that HAS affects contra-regulating mechanisms involved in perception and pain tolerance, while the a-tDCS increased the excitability of the corticospinal pathways. They give a subsidy to investigate their effect as approaches to counter regulate the maladaptive neuroplasticity involved in fibromyalgia. Clinical Trial Registration www.ClinicalTrials.gov , identifier – NCT05066568.

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BackgroundRheumatoid Arthritis (RA) patients often present chronic pain that may persist beyond therapeutic control of objective signs of inflammation [1] and may cause significant physical and psychological impairments. Complex mechanisms encompassing peripheral and central sensitization seem to be involved [2]. In fibromyalgia patients, Transcranial Direct Current Stimulation (tDCS) appears to be effective for decreasing chronic pain symptoms [3].ObjectivesTo verify the effect of active tDCS on pain and clinical symptoms in RA patients.MethodsThis double-blind randomized pilot clinical trial recruited women aged between 18 and 70 years diagnosed with RA and stable (3 months) low inflammatory status (CRP < 10 mg/L, ESR < 20 mm/h, swollen joint count ≤ 1) and persistent pain (VAS-pain > 4cm), from the Rheumatology ambulatory clinic of Hospital de Clínicas de Porto Alegre/Brazil. The patients were randomized into two different groups: active tDCS (A-tDCS) and Sham (S-tDCS). The 20 sessions of tDCS (2mA) were applied at home daily, for 20 min, 5 days/week. Main outcome was pain by visual analogue scale (VAS cm) after 4 weeks. Additional evaluations: pressure pain threshold (PPT,Kg), disease activity (DAS28-CRP), physical function (HAQ-DI), fatigue (FACIT-F), central sensitisation (Central Sensitization Inventory - CSI), and safety. The Paired-sample t test, the Wilcoxon test, the T-tests for independent samples, the Mann-Whitney test and the Generalized estimating equations (GEE) were performed using a gamma model were performed (accepted at p ≤0.05).ResultsTwelve patients have completed this pilot study (A-tDCS, n=6 and S-tDCS, n=6). At baseline, there are no differences in clinical features between groups (Table 1). After the 4-week intervention, the time of intervention was associated with changes on VAS-pain (p=0.004). There was between groups a trend towards a statistically significant difference for the A-tDCS group (p=0.063). Both groups had improvements on HAQ-DI, FACIT-F and CSI. On the other hand, the CRP, DAS28-CRP and PPT did not change (p>0.05) in both groups (Table 1). All patients reported low intensity of itch as an adverse effect during the session of tDCS.Table 1.Results at baseline and after 4 weeks of tDCS intervention within and between groups.VariableBaselineAfter tDCSA-tDCS(n=6)S-tDCS(n=6)A-tDCS(n=6)S-tDCS(n=6)Age (years), mean54.3±11.157.3±9.1--Disease duration, median8.0 (5.0-10.2)11 (6.2-30.5)--CRP, median (mg/L)3.5(2.0-10.0)2.0(1.0-3.7)3.0(1.7-7.0)2.5(1.7-8.7)DAS28-CRP, mean2.9±1.02.3±0.52.5±0.92.2±0.4HAQ-DI, mean1.7±0.41.6±0.51.0±0.5*1.1±0.6*FACIT-F, mean22.0±10.028.6±9.216.3±9.9*13.3±11.1*CSI, mean50.6±8.263.7±10.529.6±14.4*30.6±13.1*PPT (Kg), median2.2(2.0-2.9)2.3(1.8-4.2)2.6(2.8-2.8)1.9(1.1-4.2)VAS (cm),median6.5(1.7-7.0)6.0(1.7-8.7)5.0(2.5-6.0)*5.0(3.5-7.0)Leflunomida, n (%)2.0 (33,3)2.0 (33,3)--MTX, n (%)2.0 (33,3)5.0 (83,3)--bDMARDS, n (%)1.0 (16.7)0.0 (0.0)--p, Difference value at baseline and after intervention with tDCS (within groups)(p≤0.05)*.ConclusionThese preliminary findings revealed that daily treatment with tDCS compared to sham stimulation over 4 weeks may improve the chronic pain in RA patients, despite the placebo effect observed for physical function, fatigue, PPT and central sensitization. The intervention was well tolerated. Thus, tDCS appears to be a promising auxiliary tool in the treatment of patients with low-inflammation RA who have chronic pain, but larger and longer studies are needed to confirm this observation and optimize it.Reference[1] Mathias K et al. Curr Pain Headache Rep. 2021; 2. Cao Y et al. Mediat Inflamm. 2020;3. Caumo W et al. J Pain. 2022.AcknowledgementsSociedade Brasileira de Reumatologia (SBR).Disclosure of InterestsNone Declared.