Hannah Roeder, MD, MPH
Transcutaneous electrical nerve stimulation (TENS) has been regularly employed over the last half century as a pain modulatory therapy,1 and it has been explored as a therapy to improve sensorimotor function in chronic stroke patients since the 1980s. Early studies among chronic stroke patients found unilateral TENS (over the affected leg) improved lower limb spasticity and strength.2 Subsequently, unilateral TENS plus task-related training was found to be superior to TENS alone in improving lower extremity spasticity, strength, and gait velocity.3 Similar benefits of adding task-related training to TENS were subsequently shown for upper limb motor function.4 More recently, bilateral TENS (Bi-TENS) combined with task-oriented training (TOT) was superior to unilateral TENS (Uni-TENS)+TOT in a trial investigating lower extremity strength and gait performance.5 The current study by Chen and colleagues investigates Bi-TENS+TOT in upper limb motor recovery.
The authors used a 4-group parallel design: Bi-TENS+TOT, Uni-TENS+TOT, placebo-TENS+TOT, and a control group without treatment. Inclusion criteria included age 50 to 80 years, diagnosed with stroke 1 to 10 years ago, volitional control of the non-paretic arm, at least minimal antigravity movement in the paretic shoulder, at least 5 degrees of wrist extension, and an Abbreviated Mental Test Score >/=7. Patients with contraindications to TENS, uncontrolled medical conditions, receptive aphasia, upper limb peripheral neuropathy, enrollment in another clinical trial, or severe upper limb contractures were excluded. 120 participants were recruited and randomized to one of the 4 groups. The 3 intervention groups received 20 sessions of 60-minute treatments over 7 weeks. Stimulation was applied at an intensity twice the sensory threshold and below the motor threshold to stimulate the median nerve and the superficial radial nerve on the paretic side for the Uni-TENS group and on both sides for the Bi-TENS group, and participants completed upper limb TOT involving stetching, mobility, strengthening, dexterity, and coordination tasks. The primary outcome measure was the Fugl-Meyer Assessment of Upper Extremity (FMA-UE), which was assessed at baseline, mid- and post-intervention, and 1-month and 3-month follow-up.
The investigators found that the Bi-TENS+TOT group showed significantly greater improvement in the FMA-UE scores than the Uni-TENS+TOT (mean difference 2.13, p=0.004), placebo (2.63, p<0.001), and control (3.11, p<0.001) groups at post-intervention, and that BiTENS+TOT (mean difference 3.39, p<0.001) and Uni-TENS+TOT (1.26, p=0.018) showed significant within-group improvement in the FMA-UE at post-intervention, and the effect persisted until 3-month follow-up. There were no adverse events reported. The authors propose that Bi-TENS may be more effective than Uni-TENS due to improved interactions between the intact and lesioned hemispheres and/or due to enhanced corticomuscular activation via uncrossed contralesional corticospinal pathways. While the results in this trial were statistically significant, whether the differences in FMA-UE scores between the Bi-TENS-TOT and the other arms is clinically significant is less clear. Prior research estimated that a clinically important difference in FMA-UE scores ranged from 4.25 to 7.25 points.6 The authors noted that other limitations include challenges in blinding participants regarding their treatment group, follow-up period limited to 3 months, and potentially limited external generalizability.
Advances in stroke recovery therapeutics offer exciting possibilities for improving function and quality of life for stroke patients. Many questions remain, however, when it comes to using TENS and other similar approaches in stroke rehabilitation, including when the treatment should be given, what is the effective dose (duration, frequency, intensity), which patients benefit most, and how they can be best combined with other therapies. The current study suggests BiTENS+TOT may be an effective and safe therapy for chronic stroke patients, but more research is needed to identify the neurophysiologic mechanisms, the ideal treatment regimen, whether the therapy improves patient clinical function and quality of life, and if the interventions are cost-effective.
References:
1. Augustinsson L-E, Bohlin P, Bundsen P, Carlsson C-A, Forssman L, Sjöberg P, et al. Pain relief during delivery by transcutaneous electrical nerve stimulation. Pain. 1977;4:59-65
2. Levin MF, Hui-Chan CW. Relief of hemiparetic spasticity by tens is associated with improvement in reflex and voluntary motor functions. Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section. 1992;85:131-142
3. Ng SS, Hui-Chan CW. Transcutaneous electrical nerve stimulation combined with task-related training improves lower limb functions in subjects with chronic stroke. Stroke. 2007;38:2953-2959
4. Jung K, Jung J, In T, Kim T, Cho H-y. The influence of task-related training combined with transcutaneous electrical nerve stimulation on paretic upper limb muscle activation in patients with chronic stroke. NeuroRehabilitation. 2017;40:315-323
5. Kwong WH. Effects of bilateral cutaneous electrical stimulation in improving lower limb motor functions and level of community integration in people with stroke. 2018
6. Page SJ, Fulk GD, Boyne P. Clinically important differences for the upper-extremity fugl-meyer scale in people with minimal to moderate impairment due to chronic stroke. Phys Ther. 2012;92:791-798
