Effects of Transcranial Direct Current Stimulation Combined with Peripheral Electrical Stimulation on Upper Limb...

Transcranial direct current stimulation (tDCS) and peripheral electrical stimulation (PES) have each demonstrated potential benefits for upper limb motor recovery in stroke patients. Their combined use has been hypothesized to produce synergistic/additive effects by engaging both central and peripheral neuroplasticity. This review aims to provide updated evidence on the effects of combined tDCS with PES on upper limb motor function and activity performance in stroke patients.

Following PRISMA guidelines, six databases were searched. A systematic review and random-effects meta-analysis were completed. Methodological quality was assessed using the PEDro scale, risk of bias was assessed using the version 2 of the Cochrane risk-of-bias tool for randomized trials (RoB 2), and certainty of evidence was assessed using the GRADE approach.

Twelve RCTs involving 449 participants were included in this review. Adding motor-level PES to tDCS demonstrated a significant benefit on FMA-WH (MD = 1.53; 95% CI = 0.38 to 2.68; p = 0.009; low certainty; single study), while no significant effects on FMA-UE, MAS, ADL, and activity capacity were observed. Adding tDCS to motor-level PES yielded no significant benefits on FMA-UE and FMA-WH, while significant effects on handgrip strength and activity capacity were seen (with low certainty based on narrative reporting from individual studies). Adding tDCS to sensory-level PES showed no significant effects on FMA-UE, FMA-WH, MAS, muscle strength, and activity capacity. Adding tDCS and motor-level PES to standard therapy showed non-significant effect on FMA-UE, while significant benefits on FMA-WH (MD = 5.17; 95% CI = 4.09 to 6.25; p < 0.001), ADL (MD = 17.07; 95% CI = 15.54 to 18.60; p < 0.001), and MAL-AOU (with low certainty based on a single study) were observed. Adding tDCS and sensory-level PES to standard therapy demonstrated no significant overall effects on FMA-UE&LE (MD = 10.57; 95% CI = -32.29 to 53.43; p = 0.197, I² = 43%), MAS (MD = -2.29; 95% CI = -13.09 to 8.51; p = 0.227; I² = 57%), and ADL (MD = 12.16; 95% CI = -44.69 to 69.02; p = 0.224; I² = 69%) (with low certainty based on multi-arms from a single study). Exploratory meta-analysis suggested a possible significant ADL improvement by combining tDCS and either motor/sensory PES with standard therapy (MD = 14.37; 95% CI = 1.83 to 26.91; p = 0.039; I² = 71%)(with very low certainty).

This review revealed that the current evidence, although of very low certainty, does not demonstrate a clear synergistic/additive effect of combined tDCS and PES on upper limb motor function recovery after stroke (which may be due to the substantial heterogeneity and various state-dependent responses across cohorts). Current evidence suggests a potential ADL improvement after stroke by pairing tDCS and PES with conventional rehabilitation; however, this was of very low certainty which requires future studies to further validate. Future studies should use factorial designs (comparing tDCS with PES, tDCS alone, PES alone, and sham or standard therapy control) to further verify the effect of pairing tDCS and PES on upper limb function after stroke.