Age as a Mediator of tDCS Effects on Pain: An Integrative Systematic Review and Meta-Analysis

Abstract

Introduction: The transcranial direct current stimulation (tDCS) is a neuromodulatory technique with the potential to decrease pain scores and to improve chronic pain treatment. Although age is an essential factor that might impact the tDCS effect, most studies are solely conducted in adults. Therefore, the age limitation presents a critical research gap in this field and can be shown by only a handful of studies that have included other age groups. To examine the evidence upon the tDCS effect on pain scores on children, adolescents, or elderly, and indirectly, to infer the age-dependent impact on tDCS effects, we conducted a systematic review and meta-analysis. Methods: A systematic review searching the following databases: PubMed, EMBASE, and Science Direct using the following search terms adapted according to MeSh or Entree: [("Adolescent" OR "Children" OR "Elderly") AND ("tDCS") AND ("Pain" OR "Pain threshold") AND ("dorsolateral prefrontal cortex" OR "Motor cortex)] up to April 20th, 2020. We retrieved 228 articles, 13 were included in the systematic review, and five studies with elderly subjects that had their outcomes assessed by pain score or pain threshold were included in the meta-analysis. Results: For the analysis of pain score, 96 individuals received active stimulation, and we found a favorable effect for active tDCS to reduce pain score compared to sham (P = 0.002). The standardized difference was −0.76 (CI 95% = −1.24 to −0.28). For the pain threshold, the analysis showed no significant difference between active and sham tDCS. We reviewed two studies with adolescents: one study using anodal tDCS over the prefrontal cortex reported a reduction in pain scores. However, the second study reported an increase in pain sensitivity for the dorsolateral prefrontal cortex (DLPFC) stimulation. Conclusion: Our findings suggest tDCS may reduce pain levels in the elderly group. Nevertheless, the small number of studies included in this review-and the considerable heterogeneity for clinical conditions and protocols of stimulation present-limits the support of tDCS use for pain treatment in elderly people. Larger studies on the tDCS effect on pain are needed to be conducted in elderly and adolescents, also evaluating different montages and electrical current intensity.

Central Post-Stroke Pain: An Integrative Review of Somatotopic Damage, Clinical Symptoms, and Neurophysiological Measures

“…The decreases in ICF and SICI found in the study of Hosomi et al (126) are likely more critical in their contrast with the findings of the study of Tang et al (125). In assessing CE, several factors might explain intra-subject variability, including age (130,131), sex (130), sleep deprivation (132), the severity of the disease (133), CNS drugs (i.e., anticonvulsants, antidepressants, benzodiazepines, and opioids) (134), and structural damage (65,112). Hence, we should interpret the nature of the small variability in MT and MEP with parsimony since several reasons may explain these findings, as shown below.…”

“…Therefore, these effects were associated with changes in somatosensory cortex organization (159). From this set of data, it is possible to suppose that there are sensory and motor manifestations consequent to the same structural lesions in the CNS, which concurs with specific adaptive cortical changes, but with different evolution and responses to therapeutic approaches due to a neuroplasticity state influenced by varying degrees of physiological, biological, and social factors (131,160,161).…”

Pain reduction in fibromyalgia syndrome through pairing transcranial direct current stimulation and mindfulness meditation: A randomized, double-blinded, sham-controlled pilot clinical trial

“…However, a study comparing the differences in effects of anodal tDCS over M1 between young and elderly adults shows no significant differences in corticospinal excitability ( 94 ). Furthermore, according to a meta-analysis by Saldanha et al ( 95 ), the analgesic effects following anodal tDCS over M1 compared to sham does not differ between elderly and younger patients ( 95 ). Moreover, despite a sex-matched design, both participating males were allocated in the sham group.…”