Effect of Thermal Stimulation on Upper Extremity Motor Recovery 3 Months After Stroke
Background and Purpose—To examine the effect of thermal stimulation (TS) on upper extremity (UE) motor recovery in patients at least 3 months after stroke.
Methods—Participants were randomly assigned to either the experimental group or the control group. In addition to regular rehabilitation programs, the experimental group received an UE-TS protocol for 30 minutes per day (3 days/week for 8 weeks); the control group received the same TS protocol on lower extremity. The UE subscale of the Stroke Rehabilitation Assessment of Movement and the Action Research Arm Test were primary outcome measures. The Modified Ashworth Scale and the Barthel Index were secondary outcome measures. All measures were administered at baseline, after TS, and at 1-month follow-up.
Results—Twenty-three participants (12 in the experimental group) completed the study. After treatment, the experimental group showed significant improvement compared to the control group in the scores of the UE subscale of the Stroke Rehabilitation Assessment of Movement and Action Research Arm Test. At follow-up examination, a significant improvement in the experimental group was observed on the UE subscale of the Stroke Rehabilitation Assessment of Movement.
Conclusions—The 8-week additional UE-TS protocol improved UE motor recovery for stroke patients 3 months after onset.
Thermal stimulation (TS)1 recently has been developed to promote upper extremity (UE) recovery in stroke patients because TS may induce cortical reorganization.2,3 Chen et al1 applied hot/cold packs on acute stroke patients and found improvement on UE motor and sensory function. However, the effect of TS on UE recovery in subacute or chronic stroke patients remains unknown. We investigated the effect of TS on the paretic UE at least 3 months after stroke using custom-made thermal stimulators that provided TS with stable temperatures.
Materials and Methods
This was an assessor-blinded, block-randomized, controlled study. Participants were recruited from a university hospital. The inclusion criteria were: (1) first-ever unilateral stroke; (2) stroke onset >3 months and <3 years; (3) ability to follow verbal instructions; (4) age between 18 and 80 years; and (5) ability to sit on a chair for >30 minutes and move paretic hand away from thermal therapeutic pad independently, with and without the assistance of the nonparetic hand. The exclusion criteria were: (1) musculoskeletal or cardiac disorders that could interfere with experimental tests; (2) diabetic history or sensory impairment attributable to peripheral vascular disease or neuropathy; (3) skin injuries at the sites of stimulation; and (4) contraindication of heat or ice application.
Thirty-one participants were recruited and they signed informed consent. Eight were excluded because of ineligibility (n=6) and refusal (n=2). Eligible participants were allocated randomly to either the experimental group or the control group. All participants were assessed by a physical therapist blinded to group allocation.
The research protocol was approved by the ethics committees. This study is registered at ClinicalTrials.gov (NCT01078727).
All participants received regular outpatient rehabilitation (3 times per week) in the study periods. Each session of the rehabilitation included 1 hour of physical therapy and 1 hour of occupational therapy. The experimental group received an additional UE-TS protocol for 30 minutes (3 times per week for 8 weeks). The control group received the same TS protocol on the lower extremity.
Participants in the experimental group were comfortably seated with their hands placed on a table. Two thermal stimulators and two therapeutic pads (Model B401L; Firstek Scientific Co) were used to provide TS (hot or cold) at constant temperatures. Each thermal stimulator was connected to a thin (1-mm) and flexible TS therapeutic pad (38×56 cm) in the closed-loop water system. The temperature of the hot-pad surface was stable (46°C–47°C). That of the cold-pad surface was also stable, ranging from 7°C to 8°C. The therapeutic pad was wrapped around the paretic hand and distal arm in the UE-TS protocol. In the TS protocol on lower extremity, the therapeutic pad was wrapped around the distal lower leg and the dorsal foot.
Intensities for thermal pain were chosen based on participants’ perceived pain thresholds and pain perception. Participants were informed of possible adverse effects and were instructed to rate their discomfort using a 10-cm visual analog scale ranging between 0 (no pain) and 10 (maximum tolerable pain). During the development of discomfort (visual analog scale score >7), participants were encouraged to actively move their paretic hands away from the stimuli or to generate a reflex. To induce voluntary/reflexive movement after TS, ceiling durations of heating and cooling stimulation were limited to 15 seconds and 30 seconds, respectively. During TS intervention on UE, the heating pad was put on the paretic hand 10 times, interleaved with 30-second pauses. Participants were encouraged to withdraw or move the paretic hand from the heating pad when discomfort occurred or after 15 seconds of stimulation. During the 30-second pause period, participants were encouraged to perform voluntary paretic wrist and elbow extensions. After 10 occurrences of heating stimulation, the cold stimulation procedure began. A session of TS entailed 2 alternate cycles of heat and cold stimulation.
Primary outcome variables were the UE subscale of the Stroke Rehabilitation Assessment of Movement and the Action Research Arm Test. Secondary outcome variables were the Modified Ashworth Scale, the lower extremity subscale of the Stroke Rehabilitation Assessment of Movement, and the Barthel Index. All outcome measures were administered at baseline, week 8 (after treatment), and week 12 (follow-up).
Repeated-measures analyses of variance followed by post hoc analysis were used to analyze the results. The change score of each measure between both groups was examined with Mann-Whitney U tests.
All 23 participants completed the study. No adverse events (burns or pain) were reported. We found no significant differences between 2 groups at baseline (Table 1).
The interaction parameter (“time by group”) was significant for the score on the UE subscale of the Stroke Rehabilitation Assessment of Movement, Action Research Arm Test, and Modified Ashworth Scale of elbow flexors and wrist flexors (P<0.05; Table 2).
The experimental group displayed greater improvements on the scores of the UE subscale of the Stroke Rehabilitation Assessment of Movement and Action Research Arm Test than did the control group at week 8 (after treatment), with a significant between-group difference (P<0.05). At follow-up examination, a significant improvement in the experimental group as compared to the control group was observed on the UE subscale of the Stroke Rehabilitation Assessment of Movement and Modified Ashworth Scale of elbow flexors (Table 3).
A “plateau phase” of UE recovery may have been reached at 3 months after stroke.4 Our results indicate that an additional UE-TS protocol could provide further improvement in motor function of UE than those in the control group after 3 months of onset.
TS not only provides somatosensory stimulation but also uses the forced-use strategy to provoke volitional/reflexive motor activity. Although the mechanism of the effect of TS on stroke patients remains unknown, it has been proposed that somatosensory stimulation may induce plasticity in stroke patients.5 Further studies are needed to investigate the underlying mechanisms responsible for the effects of TS on UE recovery.
TS was developed as a low-cost and practicable intervention. Previously, TS was provided through general hot/cold packs, but it was difficult to provide constant temperature stimulation and avoid tissue damage. In this study, we used thermal stimulators to provide stable TS. No adverse events were reported by the patients. Therefore, TS appears to be a safe intervention for stroke patients. However, potential complications during TS may form barriers to compliance. In future studies, optimal therapeutic parameter settings must be established based on safety and efficacy, namely temperature settings, frequency, and intensity of TS.
The experimental group showed greater improvements in the spasticity of elbow and wrist flexors after 8 weeks of TS; forced use of the paretic hand was a possible reason. However, further studies are needed to determine the effect of TS on spasticity reduction.
Three limitations are noted. First, we did not investigate the effect of TS on somatosensory recovery. Additional studies are required to explore the effects of TS on sensory functions, including pain thresholds and cortical representations. Second, we did not include patients older than 80 years because of safety concerns. Third, the sample size of this study was small; therefore, the generalizability of our results is limited. A large-scale trial is necessary to explore the best dose–response characteristics of TS.
Sources of Funding
This study was supported by research grants from the National Science Council (NSC 96-2314-B-037-028) and the National Health Research Institutes (NHRI-EX99-9907PI) in Taiwan.
The statistical analysis was conducted by H.C. Wu and Dr J.H. Lin. The concept for the article was developed by Drs. J.H. Lin, M.J. Hsu, and C.L. Hsieh. H.C. Wu, Y.C. Lin, and S.M. Liu acquired the data. All authors reviewed and made critical revisions to the final manuscript.
- Received June 15, 2010.
- Accepted June 29, 2010.
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