Our findings support the validity and reliability of the BP-PCS. The scale showed satisfactory psychometric properties. CFA provides support for the three-factor structure reported in previous studies. This factor structure presented good discriminative properties to identify catastrophizers who present with mild chronic pain, fibromyalgia, and CTH. The BP-PCS is a valuable tool for use in scientific studies and in the clinical setting in patients with chronic pain in Brazilian Portuguese-speaking countries.

Transcranial Direct Current Stimulation (tDCS) is a non-invasive brain stimulation technique that is affordable and easy to operate compared to other neuromodulation techniques. Anodal stimulation increases cortical excitability, while the cathodal stimulation decreases it. Although tDCS is a promising treatment approach for chronic pain as well as for neuropsychiatric diseases and other neurological disorders, several complex neurobiological mechanisms that are not well understood are involved in its effect. The purpose of this systematic review is to summarize the current knowledge regarding the neurobiological mechanisms involved in the effects of tDCS. The initial search resulted in 171 articles. After applying inclusion and exclusion criteria, we screened 32 full-text articles to extract findings about the neurobiology of tDCS effects including investigation of cortical excitability parameters. Overall, these findings show that tDCS involves a cascade of events at the cellular and molecular levels. Moreover, tDCS is associated with glutamatergic, GABAergic, dopaminergic, serotonergic, and cholinergic activity modulation. Though these studies provide important advancements toward the understanding of mechanisms underlying tDCS effects, further studies are needed to integrate these mechanisms as to optimize clinical development of tDCS.

Endometriosis-associated chronic pelvic pain (EACPP) presents with an intense inflammatory reaction. Melatonin has emerged as an important analgesic, antioxidant, and antiinflammatory agent. This trial investigates the effects of melatonin compared with a placebo on EACPP, brain-derived neurotrophic factor (BDNF) level, and sleep quality. Forty females, aged 18 to 45 years, were randomized into the placebo (n = 20) or melatonin (10 mg) (n = 20) treatment groups for a period of 8 weeks. There was a significant interaction (time vs group) regarding the main outcomes of the pain scores as indexed by the visual analogue scale on daily pain, dysmenorrhea, dysuria, and dyschezia (analysis of variance, P < 0.01 for all analyses). Post hoc analysis showed that compared with placebo, the treatment reduced daily pain scores by 39.80% (95% confidence interval [CI] 12.88-43.01%) and dysmenorrhea by 38.01% (95% CI 15.96-49.15%). Melatonin improved sleep quality, reduced the risk of using an analgesic by 80%, and reduced BNDF levels independently of its effect on pain. This study provides additional evidence regarding the analgesic effects of melatonin on EACPP and melatonin's ability to improve sleep quality. Additionally, the study revealed that melatonin modulates the secretion of BDNF and pain through distinct mechanisms.

This study provides additional evidence supporting the analgesic effects of melatonin on pain scores and analgesic consumption in patients with mild-to-moderate chronic myofascial TMD pain. Furthermore, melatonin improves sleep quality but its effect on pain appears to be independent of changes in sleep quality.