Table 1 Summary of the methodology and results from the studies reviewed
From: Peripheral electrical stimulation to reduce pathological tremor: a review
Article | Population | Strategy | Stim. location | Stim. pulse width [us] | Stim. frequency [Hz] | Stimulation protocol | Tremor assessment | Main results | Physiological mechanism |
|---|---|---|---|---|---|---|---|---|---|
Bó et al. [20] | 10 ET (moderate-severe) | FES: co-contraction | SF: heterogeneous wrist and finger muscles | 150 | 40 | 10-50 s/trial, stim ON vs stim OFF, 5–7 trials | Kinematics, tremor power at wrist | Most significant acute tremor attenuation: 37.18%-94.68% | Increasing joint stiffness |
Britton et al. [38] | 10 ET; 9 PD, 8 HV | Single shock > MT | SF: median nerve | 500 | Single shock | Single shock | sEMG | Significant EMG reduction from 90 to 210 ms post stimulus | Afferences reset central tremor oscillators |
Dideriksen et al. [42] | 4 ET; 5 PD (mild-severe) | afferent < MT: out-of-phase EMG based | SF (2 ET, 3 PD), IM (2 ET, 2 PD): wrist flexors-extensors | 400 | 100 | 150 s/trial, stim ON vs stim OFF, 20% and 40% DC, 10 trials | Kinematics, tremor power at wrist | Average highest acute reduction: 54 ± 20% (IM) and 50 ± 41% (SF) | Ia afferent fibers, reciprocal inhibition |
Dosen et al. [16] | 2 ET; 4 PD (mild-severe) | FES and afferent < MT: out-of-phase EMG based | SF: wrist/finger flexors-extensors | 300 | 100 | 120 s/trial, stim ON vs stim OFF, 5 trials per modality | Kinematics, tremor power at wrist | Average acute reduction: 60 ± 14% (> MT) and 42 ± 5% (< MT) (p < 0.05) | Generation of opposite forces to tremor oscillations; Ia afferent fibers, reciprocal inhibition |
Gallego et al. [39] | 4 ET; 2 PD (mild-severe) | FES: co-contraction | SF: wrist flexors-extensors | 250 or 300 | 30 or 40 | 30 s/trial; stim ON vs stim OFF, 6–12 trials | Kinematics, tremor power at wrist | Average acute reduction: 52.33 ± 25.48% (p < 0.05) | Increasing joint stiffness |
Gillard et al. [29] | 3 PD, 3 HV | FES: out-of-phase accelerometer based | SF: wrist/finger flexors-extensors | * | * | 30 s/trial, stim ON vs stim OFF, 10 trials | Kinematics at finger/wrist | Average acute reduction: 84.50 ± 2.20% | Out-of-phase forces |
Grimaldi et al. [17] | 1 PD, 1 ET, 1 cerebellar syndrome | FES: co-contraction | SF: wrist/elbow flexors-extensors | 100 | 30 |  ~ 30 s/task, stim ON vs stim OFF, 15 trials (5 tasks) | Kinematics at finger/wrist/elbow; CNF-TES scale | Most significant acute tremor attenuation in one ET patient: ~ 50% | Increasing joint stiffness |
Hao et al. [32] | 8 PD (moderate) | afferent < MT: continuous (EMG triggered) | SF: radial nerve (dorsal skin of hand) | 200 | 250 | 15 s/trial, stim OFF(5 s)- ON(5 s)-OFF(5 s), 9–13 trials | Kinematics and sEMG at finger/wrist/elbow flexors-extensors | Average acute reduction: 61.56 (kinematics across degrees of freedom); 47.97% EMG across degrees of freedom) | Cutaneous afferents and propriospinal interneurons |
Heo et al. [21] | 18 ET (moderate) | afferent < MT: continuous | SF: wrist/elbow flexors-extensors | 300 | 100 | 15 s/trial, Pre-Stim ON-Post 5 min, 9 trials | Kinematics at finger/forearm/arm | Average acute reduction: 90% (finger), 58% (hand), -50% (forearm); Post 5 min: 88% (finger), 61% (hand), 27% (forearm) | Afferences might modulate supraspinal tremor oscillators |
Heo et al. [22] | 18 ET (mild-severe) | afferent < MT: continuous | SF: wrist/elbow flexors-extensors | 300 | 100 | Spiral drawing task, Pre-Stim ON-Post 5 min, 9 trials | Kinematics at finger/forearm/arm | Acute average reduction: 12%. Significant differences (p < 0.05) for Pre-Stim and ON-Post 5 min | Afferences might modulate supraspinal tremor oscillators |
Heo et al. [34] | 14 PD (mild-severe) | afferent < MT: continuous | SF: wrist flexors-extensors | 300 | 100 | 15 s/trial, Pre-Stim ON-Post 5 min, 9 trials | Kinematics at finger/forearm/arm | Reduction in 50–71% of patients. Average acute: 68% (finger), 62% (hand), 53% (forearm); Post 5 min: 56% (finger), 59% (hand), 60% (forearm) | Afferences might modulate supraspinal tremor oscillators |
Heo et al. [35] | 14 PD (same Heo et al. [34]), 9 SWEEDs | afferent < MT: continuous | SF: wrist flexors-extensors | 300 | 100 | 15 s/trial, Pre-Stim ON-Post 5 min, 9 trials | Kinematics at finger/forearm/arm | No reduction data. Only significant differences (p < 0.05) for Pre-Stim ON in PD. No reduction for SWEEDs | Afferences might modulate supraspinal tremor oscillators |
Isaacson et al. [26] | 263 ET (mild-severe) | afferent < MT: out-of-phase kinematics (open-loop) | SF: radial and median nerves at wrist | †| †| Clinical-trial: 3 months, 2 × 40 min stim session/day | TETRAS, select BF-ADL tasks, kinematics at wrist, CGI-I, PGI-I, QUEST | 62% (TETRAS) and 68% (BF-ADL) of severe/moderate patients improving to mild/slight | Afferences modulate ventral intermediate nucleus |
Javidan et al. [40] | 3 ET, 4 PD, 6 cerebellar tremor | FES: out-of-phase kinematics based | SF: wrist, elbow flexors-extensors | 100 | 30 | 20 min/trial, Stim ON vs Stim OFF, unknown number of trials | Kinematics at wrist | Average acute reduction at wrist: 73 ± 14% (ET), 62 ± 5% (PD), 62 ± 38% (cerebellar tremor) | Generation of opposite forces to tremor oscillations |
Jitkritsadakul et al. [30] | 34 PD (moderate) |  > MT: continuous | SF: fingers APB, FDI, SDI | 150 | 50 | 10 s/trial, Pre-Stim ON, 2 trials | Kinematics and sEMG at finger/forearm/arm; UPDRS | Average acute reduction (tremor power): 49.57 ± 38.89% (p < 0.05) | Afferences interfere with the cerebello-thalamo-cortical circuit |
Jitkritsadakul et al. [33] | 30 PD (moderate) |  > MT: continuous | SF: fingers APB, FDI, SDI | 150 | 50 | 10 s stim, Pre-Stim ON; 30 min session; Sham vs Stim | Kinematics at hand (glove); UPDRS; VAS | Average acute reduction (RMS, x-axes): 60.22 ± 38.85% (p < 0.05); significantly different from sham group | Afferences interfere with the cerebello-thalamo-cortical circuit |
Kim et al. [25] | 9 ET (moderate-severe) | afferent < MT: out-of-phase kinematics based and open-loop | SF: radial nerve at wrist | 200 | 50, 100, 200 | 20 s/trial, stim. OFF (10 s)-ON (10 s); open-loop, closed-loop; 12.5%, 25% and 37% DC; 18 trials | Kinematics at wrist; TETRAS; qualitative assessment | Average acute reduction: 42.17 ± 3.09% (p < 0.05). No differences open vs closed loop | Not proposed |
Lin et al. [23] | 23 ET (moderate-severe) |  < MT: out-of-phase kinematics (open-loop) | SF: radial and median nerves at wrist | 300 | 150 | Pre, 40 min stim, Post; Sham vs Stim group | TETRAS (spiral) | Average post reduction (TETRAS): 60 ± 8.4% (p < 0.05), significantly different from sham group | Afferences modulate ventral intermediate nucleus |
Mones et al. [28] | 5 PD | Single shock above MT | SF: ipsilateral and contralateral ulnar nerve at wrist | 500 | Single shock | Single shock | iEMG | No change in tremor amplitude. Change in tremor frequency after shock | Afferences reset central tremor oscillators |
Munhoz et al. [18] | 5 ET, 2 peripheral neuropathy | TENS > MT: continuous | SF: brachial plexus on neck, C7 spinous process | 250 | 5, 10, 50, 100 | Pre, 15 min stim, Post | Kinematics at wrist, WHIGET scale | No significant reduction | Wrong afferent fibers targeted or stimulation parameters |
Muceli et al. [36] | 1 PD | afferent < MT: out-of-phase EMG based | SF: wrist/finger flexors-extensors | 200 | 100 | 60 s/trial, stim ON(30 s) vs stim OFF(30 s), 2 trials | Kinematics, tremor power at wrist | Acute reduction in one patient: 58% | Ia afferent fibers, reciprocal inhibition |
Pahwa et al. [24] | 77 ET (moderate-severe) | afferent < MT: out-of-phase kinematics (open-loop) | SF: radial and median nerves at wrist | 300 | 150 | Pre, 40 min stim, Post; Sham vs Stim group | TETRAS, select BF-ADL tasks, CGI-I scale | Average post reduction (task 4 TETRAS): 46% (stim group) different from 24% (sham group) | Afferences modulate ventral intermediate nucleus |
Pascual-Valdunciel et al. [27] | 11 ET (moderate) | afferent < MT: EMG based (SATS), continuous | SF: median and radial nerves at arm; IM: FCR and ECR | 400 (SF), 200 (IM) | 100 | Pre; 60 s/trial, stim ON(30 s) vs stim OFF(30 s), > 6 trials, continuous/SATS; Post; Post24h | Kinematics at wrist/elbow/shoulder; FTM scale; contralateral arm | Average acute reduction at wrist: 32%; Post reduction after SATS-IM (6/6) patients | Ia afferent fibers, reciprocal inhibition, propriospinal system |
Popovic et al. [41] | 3 ET, 4 PD, 5 HV | FES: out-of-phase EMG based | SF: wrist, elbow flexors-extensors | 250 | 40 | approx. 60 s/trial, stim ON vs stim OFF** | Kinematics at wrist | Average acute reduction: 67 ± 13% | Generation of opposite forces to tremor oscillations |
Spiegel et al. [37] | 8 PD |  > MT | SF: median (IP and CL) and ulnar (IP) nerves at wrist | 200 | 2, 3, 5 | approx. 316 s/trial, single shock, post 5 min, 4 trials without shock-4 trials with shock | sEMG | Tremor amplitude not reported. Change in tremor frequency after stimulation | Afferences interfere with central tremor oscillators |
Widjaja et al. [19] | 1 ET | FES: out-of-phase model based (EMG + kinematics) | SF: wrist flexors-extensors | 200 | 25 | 40 s/trial, Stim ON vs Stim OFF, 1 trial | Kinematics at wrist | Individual acute tremor attenuation: 57% | Generation of opposite forces to tremor oscillations |
Xu et al. [31] | 2 PD (moderate) | afferent < MT: continuous (EMG triggered) | SF: radial nerve (dorsal skin of hand) | 200 | 250 | 15 s/trial, stim OFF(5 s)-ON(5 s)- OFF(5 s), 9–13 trials | Kinematics and sEMG at finger/wrist/elbow flexors-extensors | Significant acute reduction compared to OFF (p < 0.05). No values provided | Cutaneous afferents and propriospinal interneurons |