Mirror Therapy Enhances Lower-Extremity Motor Recovery and Motor Functioning After Stroke: A Randomized Controlled Trial

Methods 

Design 

We used an assessor-blinded, randomized controlled design. The same investigator (SS), who was blinded to the treatment assignment, performed all the assessments. After baseline measurements were obtained, the patients were randomly assigned to either the mirror group (n=20) or the control group (n=20), using computer-generated random numbers (fig 1). Blocks were numbered, after which we used a random-number generator program to select numbers that established the sequence in which blocks were allocated to one or the other group. A physician who was blinded to the research protocol and was not otherwise involved in the trial conducted the random-number program.

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Fig 1. Flow diagram for randomized subject assignment in this study.

Results 

Demographic and clinical characteristics of the 40 participants, as well as baseline comparisons of the groups, are presented in table 1. None of the patients missed more than 2 scheduled sessions. Three patients from the mirror group and 4 patients from the control group could not attend the follow-up clinic for final evaluation because of socioeconomic reasons. We did not observe any adverse events. Baseline comparisons revealed that age, gender, injury characteristics, time since stroke, Brunnstrom stages, MAS, FIM motor, and FAC scores did not differ between the groups (P>.05). All assessed outcome parameters improved significantly in both groups after the treatment and continued to improve at follow-up (table 2). The mean change score and 95% confidence interval (CI) of the Brunnstrom stages (mean, 1.7; 95% CI, 1.2–2.1; vs mean, 0.8; 95% CI, 0.5–1.2; P=.002), as well as the FIM motor score (mean, 21.4; 95% CI, 18.2–24.7; vs mean, 12.5; 95% CI, 9.6–14.8; P=.001), showed significantly more improvement at follow-up in the mirror group than in the control group. Neither MAS (mean, 0.8; 95% CI, 0.4–1.2; vs mean, 0.3; 95% CI, 0.1–0.7; P=.102) nor FAC (mean, 1.7; 95% CI, 1.2–2.1; vs mean, 1.5; 95% CI, 1.1–1.9; P=.610) showed significant differences between the groups.

Table 1. Characteristics of the 2 Study Groups

	Variable	Mirror (n=20)	Control (n=20)	P
	Age (y)	62.7±9.7	64.7±7.7	.36⁎
	Sex (women/men)	10/10	7/13	.52†
	Type of injury (ischemic/hemorrhagic)	16/4	17/3	.50†
	Paretic side (right/left)	6/14	7/13	.50†
	Time since stroke (mo)	3.5±1.3	3.9±1.9	.44⁎
	Mean Brunnstrom stages	2.4±0.7	2.5±1.0	.73†
	Median Brunnstrom stages	3.0	3.0
	Mean MAS	2.6±0.5	2.3±0.7	.13†
	Median MAS	3.0	2.0
	Mean FAC	1.9±0.5	2.0±0.7	.79†
	Median FAC	2.0	2.0
	FIM motor score	48.3±5.5	50.2±11.6	.51⁎

NOTE. Values are mean ± SD, median, or number of patients.

⁎ Student t test. † χ2 test.

Table 2. Motor Recovery, Spasticity, Walking Ability, and Motor Functioning Scores of Patients at Pretreatment, Post-Treatment, and Follow-Up

	Parameter	Group	Pretreatment	Post-Treatment	Follow-Up	Δ (95% CI)	P
	Brunnstrom stages						.002
		Mirror	2.4±0.7	3.5±0.8	4.2±0.8	1.7(1.2–2.1)
		Control	2.5±1.0	3.0±0.7	3.4±0.8	0.8(0.5–1.2)
	MAS						.102
		Mirror	2.6±0.5	2.3±0.5	1.8±0.7	0.8(0.4–1.2)
		Control	2.3±0.7	2.2±0.7	1.9±0.7	0.3(0.1–0.7)
	FAC						.610
		Mirror	1.9±0.5	2.8±0.6	3.6±0.9	1.7(1.2–2.1)
		Control	2.0±0.7	2.9±0.7	3.5±0.9	1.5(1.1–1.9)
	FIM motor						.001
		Mirror	48.3±5.5	65.9±4.8	69.9±5.9	21.4(18.2–24.7)
		Control	50.2±11.6	61.7±14.6	62.9±12.8	12.5(9.6–14.8)

NOTE. Values are mean ± SD. P values were obtained using analysis of variance for repeated measures. Abbreviation: Δ, mean change at follow-up from baseline.

Discussion 

This study reveals that in our group of stroke patients, mirror therapy combined with a conventional rehabilitation program provides additional long-term benefits in terms of lower-extremity motor recovery and motor functioning. Several recent studies on paretic upper extremity, although undersized and not sufficiently controlled, have indicated that mirror therapy may be a promising tool with which to promote motor recovery, mobility, muscle strength, dexterity and functionality after stroke.9, 10 To our knowledge, ours is the first study to investigate the effects of mirror therapy on the paretic lower extremity.

It is well known that an increased inflow of signals from sensory modalities via various ways can enhance plasticity of the brain.28 Sensory processes (including vision, audition, proprioception, touch, and pressure) can mediate feedback information that is available as a result of movement. Verbal cueing and coaxing by therapists,29 visual and auditory feedback from electromyography,30 forceplate (balance and weight shift training), computer screen (virtual reality and web-based telerehabilitation),31, 32 and kinematic feedback from an electrogoniometer33 are the most common examples used for stroke rehabilitation. In this study, we used mirror therapy to give visual feedback to the patients to enhance lower-extremity motor recovery. Studies have shown that mirror illusions have measurable effects on brain activity.16, 17, 18, 19, 20 Altschuler et al9 hypothesized that mirror therapy provides visual input of a normal movement of the affected arm in stroke patients, which may compensate for a decreased or absent proprioceptive input. Stevens and Stoykov10, 11 defined mirror therapy as a form of visually guided motor imagery, which is the mental performance of a movement without overt execution of that movement. Extensive clinical, neurophysiologic, and neuroimaging evidence demonstrates that motor imagery involves the same neural networks as motor execution.34 Another possible mechanism is the involvement of the mirror neuron system.16 Mirror neurons are bimodal visuomotor neurons that are active during action observation, mental stimulation (imagery), and action execution. For example, it has been shown that passive observation of an action facilitates M1 excitability of the muscles used in that specific action.35 Mirror neurons are now generally understood to underlie the learning of new skills by visual inspection of the skill.

In our study, all subjects performed voluntary ankle dorsiflexion movements on their nonparetic side during the therapy sessions. We selected ankle dorsiflexion because it represents selective motor control in the lower extremity after stroke. Ankle movement training is known to facilitate brain reorganization, and the angle paradigm may serve as an ongoing physiologic assay of the optimal type, duration, and intensity of rehabilitative gait training.36 In the lower extremity, voluntary ankle dorsiflexion is a way of indicating the achievement of selective motor control.22 Once voluntary movement is achieved (Brunnstrom motor recovery stage II recovery or beyond), synergistic patterns are then modified to selective (out-of-synergy) patterns.

In this study, in contrast to motor recovery and motor functioning, the between-group difference was not significant for walking ability and spasticity. Spasticity has a complex pathophysiology that enhanced visual feedback may not be sufficient to influence or control. Walking is also a complex performance and requirements for normal gait include (but are not limited to) muscle strength, coordination, balance, endurance, etc. For motor learning to be successful, the desired motor task must be practiced in a pattern that is as close to normal as possible37 and practiced intensively.38 Our intervention did not provide for practice of a gait pattern that is close to normal. It is believed that repeated task-specific protocols induce brain reorganization that facilitates functional improvements.39 Cognitive involvement, functional specificity, and progressive complexity of the tasks being trained are the key variables of motor training and cortical reorganization.40 We did not increase the complexity level of the training in this study. Another explanation for the lack of effect on walking ability may be that the 4 weeks (20 sessions, a total of 10h) in which the mirror therapy was applied may have been too short to produce significant benefits for such a complex activity. Kwakkel41 reported that a minimum of at least 16 hours augmentation was necessary to determine the required amount of practice needed to affect function. Because there are very few studies on the use of mirror therapy in patients with stroke, there is no widely accepted agreement on the duration, timing, and application of such a program.

Our results confirm that visual feedback via a mirror is a simple, inexpensive and, most importantly, a patient-specific treatment. We believe that incorporating mirror therapy into the conventional rehabilitation program at an early stage of treatment, and applying it for a long period of time (perhaps continuing the therapy at home after discharge), may be beneficial in improving the effects and outcome on lower-extremity motor recovery and function. The limitations of this study are the relatively small study population and the fact that we did not use imaging techniques (eg, functional magnetic resonance imaging, positron emission tomography) that might have demonstrated brain reorganization after therapy.

Conclusions 

Mirror therapy combined with a conventional rehabilitation program enhanced lower-extremity motor recovery and functioning in our subacute stroke inpatients.