Effects of Hypnotic Analgesia and Transcranial Direct Current Stimulation on Pain Tolerance and Corticospinal Excitability in Individuals with Fibromyalgia: A Cross-Over Randomized Clinical Trial

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.