There are a variety of approaches that have been investigated which employ afferent (i.e., sensory) stimulation for the reduction of spasticity in people with SCI. As noted previously, electrical stimulation, TENS, is one of the preferred methods for providing afferent stimulation. This technique differs from the approaches noted in the previous sections that involve stimulation to the motor system, whether via muscles or motor nerves. TENS may involve the stimulation of large, low threshold afferent nerves (Goulet et al. 1996) or dermatomal stimulation which is directed towards cutaneous skin receptors supplying the skin in the dermatome of the muscle of interest (Bajd et al. 1985; van der Salm et al. 2006). These methods are aimed at altering motor-neuron excitability through sensory reflex arcs, thereby reducing spasticity. An alternate approach employing electrical stimulation involves rectal probe stimulation, developed originally to enable ejaculation in males and heretofore a technique employed only within fertility clinics (Halstead & Seager 1991).
In addition, a variety of methods of mechanical or thermal stimuli to various afferent systems have also been studied. These include therapeutic massage over the spastic muscle (Goldberg et al. 1994), penile vibration (Laessoe et al. 2004; Alaca et al. 2005), the application of cold (i.e., cryotherapy) to reduce local muscle spasticity (Price et al. 1993), also irradiation of the skin overlying sensory nerves with a helium-neon laser purported to induce photochemical reactions which may trigger neural activity (Walker 1985). It should be noted that the article examining cryotherapy (i.e., Price et al. 1993) did not meet the review criteria of having 50% of subjects with SCI. The article was included in the review as individual results were presented for all subjects with SCI (N=7), enabling independent discernment of the effects on SCI (thereby meeting review criteria for studies having SCI N³3).
It should be noted that several of the modalities described in this section have not been employed in regular clinical practice and may be deemed as more investigational in nature. For example, helium-neon laser irradiation has only been employed in one investigation and has not been considered as a viable therapeutic approach. Similarly, penile and rectal stimulation, first noted as delivering potential side benefits within fertility clinic investigations, may not be acceptable forms of therapy to individuals from either a safety or a psychological perspective. Other therapies might simply be impractical to implement. For example, hippotherapy requires access to a suitable equine facility with appropriately trained individuals.
Tamburella et al. (2014) completed a crossover RCT (n=11) to study the effects of Kinesio Tape versus silk tape on spasticity. Study subjects were randomly allocated to receive either Kinesio Tape or conventional silk tape (ST) for 48 hours. After a 7-day washout period, the study subjects were crossed over and received 48 hours of the alternate treatment. Tape was applied to the soleus and gastrocnemius muscles with the knee extended and ankle at 90o passive dorsiflexion. Baseline and post-treatment spasticity assessments included MAS, PSFS, Spinal Cord Assessment Tool for Spastic Reflexes and the subscale for clonus assessment (SCATS). Study subjects who received Kinesio Tape demonstrated significant improvements from baseline to post-treatment in active and passive ROM, extended knee SCATS, MAS, PSFS (all p<0.001) and flexed knee SCATS (p<0.005), compared to the ST condition.
Transcutaneous Electrical Nerve Stimulation (TENS)
Oo et al. (2014) completed a prospective randomized controlled single-blinded clinical trial (n=16) of active 3-week course (five sessions/week) of TENS and standard physical therapy (n=8) vs standard therapy alone (n=8) to study the immediate and short-term efficacy of TENS in subacute spinal spasticity. Composite spasticity scores of ankle jerk, muscle tone, and ankle clonus scores were completed at baseline and immediately after the first and last interventions for both groups by a physiatrist familiar with the testing procedures. After the first session, statistical significance for reduction in the composite spasticity score was seen in the TENS group only (mean difference=1.75; 99%CI, 0.47-3.03; p=0.002) which was also apparent in a significant between group difference (mean difference 1.63; 99% CI, 0.14-3.11; p=0.006). After the final session, a significant improvement for the composite spasticity score was seen in the TENS group only (2.75; 99% CI, 1.31-4.19; p<0.001) along with a related significant between-group difference in the composite spasticity score (2.13; 99% CI, 0.59-3.66; p=0.001). The study demonstrated that the combination of TENS with standard physical therapy was beneficial in the synergistic reduction of clinical spasticity in both the immediate and short-term basis in the subacute phase of SCI rehabilitation.
Aydin et al. (2005) employed an RCT design to compare oral baclofen (N=10) to TENS (N=11) to the bilateral tibial nerves (i.e., innervating gastrocnemius muscle) in reducing lower limb spasticity. 15-minute sessions of TENS were applied to the tibial nerve over 15 days demonstrating significantly reduced spasticity as indicated by reductions in the following measures assessed immediately after the last treatment session: AS, PSFS, deep tendon reflex score, FIM and Functional Disability Scores and H-reflex amplitude. In addition, there were also some lasting effects over the next 24 hours as repeat testing the next day indicated continued spasticity reductions although to a lesser degree. It should also be noted that significant reductions were obtained on some measures (but not all) following a single session. However, the long-term effects were more profound after the 15 sessions than those obtained following a single session.
Other researchers have examined the effects of TENS following a single session (Bajd et al. 1985; Goulet et al. 1996; Chung & Cheng 2010; van der Salm et al. 2006). Goulet et al. (1996) employed a single 30-minute bout of TENS over the common peroneal nerve in an attempt to reduce plantar flexor spasticity in 14 individuals with SCI. This study showed significant decreases in scores for the MAS and the Achilles tendon reflex but no significant changes were seen for H-reflex amplitude. A trend for decreased clonus scores was observed but this was not statistically significant. Chung and Cheng (2010) also examined the effect of 60-minute TENS sessions over the common peroneal nerve. The authors reported a significant reduction on the Composite Spasticity score (p=0.017), and a reduction in resistance to full range passive ankle dorsiflexion (p=0.024), and ankle clonus (p=0.023). In these two studies, TENS appears to be effective in reducing spinal spasticity following a single session.
In contrast, van der Salm et al. (2006) and Bajd et al. (1985) each examined dermatomal TENS as opposed to direct nerve stimulation with conflicting results. Bajd et al. (1985), in a small pre-post trial (n=6) reported reduced spasticity in three subjects as indicated by increased relaxation indexes associated with the pendulum test. However, no mean data or group statistical analysis was provided. Van der Salm et al. (2006) conducted a more thorough analysis of the effect of a single 45-minute session of TENS to the L1 dermatome in 10 individuals with longstanding SCI (mostly AIS A) and obtained no short-term effects, although as noted in the previous section obtained benefits with motor stimulation. A critical element within these investigations of single-session effects is the precise time of assessment, relative to treatment, a detail not always precisely reported in the various studies, although van der Salm et al. (2006) assessed individuals as close as possible to treatment cessation.
Penile Vibratory Stimulation
Penile vibration has also been investigated as a method of providing sensory stimulation to reduce spasticity (Laessoe et al. 2004; Alaca et al. 2005). In particular, Laessoe et al. (2004) employed an unblinded, crossover RCT design (N=9) in which male participants either received penile vibration or no treatment followed by the opposite condition with a minimum washout period of 1 week. The MAS and PSFS were conducted in addition to an EMG assessment in which ongoing muscle activity was recorded over a 24-hour period. Penile vibration was shown to be effective in reducing spasticity as indicated by reductions in MAS scores (p<0.01) and a slight trend for reduced PSFS scores (p=0.26). These were not maintained over 24 hours. The EMG analysis showed that reduced muscle activity was most apparent in the first hour post-stimulation, and had returned to baseline by 3 hours suggesting the effect lasted no more than 3 hours. The authors attempted to include female subjects involving clitoral vibratory stimulation but were only able to recruit two subjects willing to submit to the procedure. Both women reported similar reductions in spasticity although evaluation of the effectiveness of the stimulation was more difficult (i.e., no confirmatory ejaculation). Results from Alaca et al. (2005) confirmed the overall study findings as penile vibratory stimulation in 10 males resulted in significant reductions in AS scores as assessed 3 hours after stimulation (p=0.001) and maintained at 6 hours (p=0.03) with a trend for reduced values still apparent at 24 hours (p=0.08). The longer carry over effect in this study may have been due to a prolonged stimulus period as Alaca et al. (2005) employed six, 3-minute periods of stimulation (separated by 1-minute) whereas Laessoe et al. (2004) used a single 5-minute period.
Helium-neon Laser Stimulation
Walker (1985) employed a helium-neon laser to irradiate the skin overlying sensory nerves and demonstrated a similar beneficial effect of suppressing clonus as seen with electrical stimulation of sensory nerves. This investigator employed an RCT design with a variety of small group control conditions (N=5 to N=7), but failed to report several important experimental details (i.e., method of concealment, method of analysis and statistical comparisons). This approach has not been investigated since this brief 1985 report.
Halstead et al. (1993) have evaluated another form of electrical stimulation, rectal electrostimulation, when they observed individuals undergoing this procedure, for the purpose of sperm retrieval, reporting improved spasticity. These investigators conducted a prospective pre-post trial examining the effects of a minimum of six sessions of rectal probe electrostimulation on various clinical measures of spasticity including the AS, PSFS, deep tendon reflexes and ankle clonus. Although they achieved good to excellent effects in more than half of the individuals examined including significant reductions in the AS (p<0.01) and with the effects outlasting the intervention by a mean of 8.2 hours according to individual self-report further therapeutic development of this approach has not continued.
Murillo et al. (2011) conducted a pre-post study (n=28) to determine if a decrease in muscle spasticity could be demonstrated with muscle vibration in study subjects with SCI. Muscle vibration at a frequency of 50 Hz during 10 minutes over the rectus femoris muscle was applied. The study showed significant treatment improvements in SCI study subjects with a decrease in MAS at the knee joint (p<0.001), an increase in ROM for knee extension (p=0.001) and a reduction in duration and frequency of clonus (both p≤0.006). Muscle vibration induced a significant reduction in Hmax/Mmax ratio in the control group (p=0.005) and in the individuals with SCI (p=0.001). The change was not significantly different between the two groups. Muscle vibration also induced a significant inhibition of Twave amplitude in both individuals with SCI (p=0.002), and control subjects (p=0.007). The Hmax and the Mmax were significantly smaller in the complete SCI than in the incomplete SCI (p=0.03, p=0.04) populations, and the Hmax/Mmax ratio was significantly greater in the individuals with complete SCI than in the individuals with incomplete SCI (p=0.02). The study showed that prolonged vibration on proximal extremity muscles decreased limb spasticity in study subjects in both complete and incomplete SCI.
Ness and Field-Fote (2009) examined the effect of whole-body vibration at 50 Hz on individuals with SCI for 4 weeks. Sessions occurred three times per week with four bouts of vibration occurring each day for 45 seconds each. A significant reduction in quadriceps spasticity was reported, as determined by first swing excursion, and persisted for at least 8 days.
In a small group of individuals with chronic motor incomplete SCI (N=29; Estes et al 2018, level 2 RCT), whole body vibration, across single sessions of 4 different frequency/duration parameters (with 1 week washout between sessions), did not result in quadriceps spasticity reduction as measured with the pendulum test (at baseline and immediately/15min/45min post-intevention) when compared to the sham-control group, but stretch reflex excitability was significantly dampened after high frequency/long duration whole body vibration in those participants with more severe spasticity. The whole-body vibration intervention consisted of 4 or 8, 45s bouts of 30 or 50 Hz vibration while sham-control treatment consisted of 8, 45s bouts of electrical stimulation. All bouts were interspersed with 1 minute of rest. Spasticity reduction was in part attributed to repeated sitting and standing across treatment bouts as some effect was also seen in sham- treated participants.
The effect of whole-body vibration training on ankle spasticity reduction did appear to be significant based on the work of In et al (2018; N=28; level 1b evidence). This group of participants with incomplete cervical SCI were randomly assigned to whole body vibration or placebo training. Whole body vibration included 16 minutes of 30Hz vibration, twice daily for 5 days each week over 8 weeks. Placebo training followed the same parameters with ultra low frequency vibration. Spasticity (passive resistive force) of the ankle plantar-flexors was measured with a hand-held dynamometer. The control group also showed a significant reduction in spasticity which was attributed to the standard physical therapy (range of motion, mat exercise and gait training). The added effect above this control effect was seen in the active intervention group and attributed to whole body vibration.
Afferent stimulation may also be produced via mechanical means. Goldberg et al. (1994) have employed therapeutic massage over the triceps surae muscle and assessed H-reflex amplitude to demonstrate that µ-motor neuron excitability is reduced significantly during a short 3-minute period of massage and somewhat reduced 3 minutes after but not 6 minutes after. Reductions in µ-motor neuron excitability are indicative of decreased spasticity.
The short-term effect of cryotherapy was investigated by Price et al. (1993) who used a biomechanical approach similar to that described earlier (i.e., Seib et al.1994) to monitor ankle viscoelastic stiffness through measurements of resistance torque to repetitive sinusoidal ankle movements. Although the majority of subjects were individuals with stroke or head injury, five of seven people with SCI showed a significant reduction in spasticity both immediately following cryotherapy and also at 1 hour after the cold stimulus was removed.
Sadeghi and Sawatzky (2014) completed a systematic review on the application of either whole body vibration or focal vibration for reducing spasticity. Articles were restricted to those published between 1987 and 2013 and having three or more participants >17 years of age, with chronic SCI, and who had spasticity for >4 months after their injury. Evidence was categorized according to the Centre for Evidence Based Medicine levels of evidence. Level 2B: one paper, Level 2C: one paper, Level 3B: six papers, Level 4: two papers (n=10). The authors found that there is limited support for using whole body vibration and focal vibration to manage spasticity secondary to SCI. A short-term reduction in spasticity is seen after focal vibration (frequency of 50-100Hz and amplitude of 2.5-3mm) and a 6 to 8 day decrease in spasticity was observed after 1 month of whole-body vibration at 50 Hz and 2-4 mm amplitude. Studies done by Murillo et al. (2011) and Ness and Field-Fote (2009) were also included in this literature review which did demonstrate a decrease in spasticity after use of vibration.
Galvanic Vestibular Stimulation
Galvanic vestibular stimulation involves painlessly and electrically activating the nerve in the ear that maintains balance. Galvanic vestibular stimulation applied to a small group of participants (N=7, Cobelijic et al 2018, level 4 evidence) with complete SCI did not significantly reduce lower extremity spasticity as measured by the MAS and the pendulum test, when compared to participants given a sham galvanic vestibular stimulation. That 2 participants experienced some anti-spasticity effects suggests that galvanic vestibular stimulation may be able to influence residual vestibulospinal influences over spasticity but that a better clinical and neurophysiological understanding of responders vs nonresponders is needed to optimize galvanic vestibular stimulation stimulation parameters.
There is level 1b evidence (from one RCT; Tamburella et al. 2014) that kinesio tape has short-term effects of decreasing spasticity and improving balance and gait in individuals with chronic SCI.
There is level 1a evidence (from three RCTs; Oo 2014; Chung & Cheng 2010; Aydin et al. 2005) that an ongoing program of TENS acts to reduce spasticity as demonstrated by various clinical and electrophysiological measures.
There is level 1b evidence (from a single RCT; Aydin et al. 2005) that reductions in spasticity with ongoing programs of TENS may persist for up to 24 hours.
There is level 1a evidence (from two RCTs; Oo 2014; Aydin et al. 2005) that a single treatment of TENS acts to reduce spasticity but to a lesser degree than that seen with ongoing programs of TENS.
Penile Vibratory Stimulation
There is level 1b evidence (from one RCT and one pre-post study; Laessoe et al. 2004; Alace et al. 2005) a single RCT supported by a single pre-post study that a single bout of penile vibration acts to reduce spasticity lasting for at least 3 hours and possibly up to 6 hours.
There is level 2 evidence (from one RCT; Walker 1985) that helium-neon irradiation of sensory nerves may suppress ankle clonus for up to 60 minutes following 40 seconds of stimulation.
Electrical Nerve Stimulation
There is level 4 evidence (from one pre-post study; Halstead et al. 1993) that several sessions of rectal probe stimulation reduces lower limb muscle spasticity for up to 8 hours.
There is level 4 evidence (from one pre-post study; Van der Salm et al. 2006) that electrical stimulation of the triceps surae does not significantly reduce spasticity.
There is level 1b (In et al, 2018, N=28 RCT) evidence that reflects reduced plantar-flexor spasticity resulting after whole body vibration (16 minutes, twice daily, 5 times per week over 8 weeks).
There is level 2 (Estes et al 2018, N-29 RCT) evidence supporting that single whole-body vibration sessions (4 or 8, 45 second bouts of 30 or 50Hz vibration) does not result in reduced quadriceps spasticity.
There is level 4 evidence (from one pre-post study; Murillo et al. 2011) that vibration over the rectus femoris muscle results in reduced knee spasticity and increased knee range of motion.
There is level 5 evidence (from one observational study; Ness & Field-Fote 2009) that (whole body vibration; 4, 45 second bouts of 50Hz vibration, 3 times per week over 4 weeks) results in reduced quadriceps spasticity over the short term.
There is level 4 evidence (from one pre-post study; Goldberg et al. 1994) that short periods of massage (e.g., 3 minutes) of the triceps surae results in reduced H-reflexes with the effect lasting no longer than a few minutes.
There is level 4 evidence (from one pre-post study; Price et al. 1993) that cryotherapy may reduce muscle spasticity for up to 1 hour after removal of the cold stimulus.
Extracorporal Shock Wave Therapy
There is level 4 evidence (from one pre-post study; Altindag & Gursoy 2014) that three sessions of extracorporal shock wave therapy may reduce muscle tone over the short term.
Galvanic Vestibular Stimulation
There is level 4 evidence (from one pre-post study; Cobelijic et al 2018) that better clinical and neurophysiological understanding is needed for galvanic vestibular stimulation responders vs nonresponders to potentially optimize galvanic vestibular stimulation stimulation parameters for responders.
Ongoing TENS nerve stimulation programs result in short-term reductions in spasticity which may last for up to 24 hours.
Use of TENS and standard physical therapy showed a reduction in clinical spasticity in the subacute phase of rehabilitation.
Penile vibration and rectal probe stimulation may be effective at reducing lower limb muscle spasticity for several hours.
Other forms of afferent stimulation including taping, massage, cryotherapy, helium-neon irradiation, whole-body vibration, and galvanic vestibular stimulation may result in immediate spasticity reduction but require more research to understand effects and intervention parameters.