Comparative Study on Effect of Proprioceptive Neuromuscular Facilitation and Facial Motor Imagery Techniques on Bell’s Palsy

Introduction

Bell’s palsy (BP) is an idiopathic, unilateral, acute weakness of the face in a pattern consistent with peripheral facial nerve dysfunction, and may be partial or complete, occurring with equal frequency on either side of the face.¹ Globally, the prevalence accounts for about 60% to 75% of Bell’s palsy cases.² The dysfunction of facial nerve affects unilateral side of the face where the eye closure and facial expressions such as frowning and smiling are affected. As the facial nerve supplies tear glands, salivary glands and the muscles of the small bones in the middle ear, it leads to impaired lacrimation, drooling of saliva and can trigger an increased sensitivity to sound.³

Based on various studies and evidences, management of BP includes antiviral drugs, Vitamin B drugs, corticosteroids therapy, massage, physiotherapy and acupuncture.^4,5 Facial muscle exercise training, EMG biofeedback, electrical muscle stimulation, taping, neuromuscular facilitation and motor imagery are the physiotherapy methods proposed to achieve greater improvement in facial muscle function.⁵

Proprioceptive Neuromuscular Facilitation (PNF) according to Kabat states that the rehabilitation through the global pattern of an entire muscular section that undergoes resistance facilitates the voluntary response of an impaired muscle. This can be used to treat BP conditions presenting with House Brackman (HB) grade IV or more.⁶ To emphasize a particular muscle or a desired activity, the normal sequencing of motions are changed. This is termed as Timing for emphasis. According to Kabat, contraction into a weaker muscle is directed by the energy produced by prevention of motion in a stronger synergist. The therapist can alter the normal timing by two ways: a) by preventing all the motions of a pattern excluding the one that is to be emphasized. b) by resisting an isometric or maintained contraction of the strong muscles in a pattern while exercising the weaker muscles.⁷

Brain activity is higher when subjects imagine the task.⁸ In the absence of actual sensory input, a multimodal cognitive simulation process enables the subject to represent perceptual information in the mind. This is termed as Motor imagery. Without any motor output, a dynamic mental state is observed when the image of a given motor movement is rehearsed in working memory. This improves motor learning and neural plasticity.⁹

Facial PNF technique is found to improve the prognosis of clinical recovery in Bell’s palsy. Facial dysfunction improvement was noticed in HB grades and Kabat’s rehabilitation has been proved to achieve faster recovery.¹⁰

Motor imagery is found to be effective in rehabilitation of Bell’s palsy. Findings from the studies with respect to motor imagery show improvement in facial motor function and reduction   in   synkinesis.   Hypothesis on motor imagery for bell’s palsy shows that the improvement in emotional and communicative aspects have positively improved the quality of life.¹¹

Despite many studies that found PNF and Facial motor imagery (FMI) to be effective in managing BP, a little is known about comparative effectiveness of PNF and FMI to fasten recovery, improve disability and improve facial nerve function in BP.

Materials and Methods

Fifty-two patients with Bell’s   palsy   were referred to physiotherapy by the Out-Patient Department of ENT, Neurology & Neurosurgery of Kempegowda Institute of Medical Science Hospital & Research Centre, Bengaluru. Forty-two patients met the inclusion criteria and were enrolled for the study. These patients were randomly divided into two groups according to a computer-generated simple randomization list at 1:1 ratio. Using a sample size calculator, sample size was determined, considering functional recovery of the facial palsy as the main outcome based on HB grading system (grade IV). Based on this parameter, sample size per group was calculated. Purposive sampling was done. Twenty-one patients included in Group A were treated with Proprioceptive Neuromuscular Facilitation and 21 patients in Group B were treated with Facial Motor Imagery techniques. There were two drop outs from group A and one drop out from group B.

The study included acute, unilateral, lower motor neuron Bell’s palsy patients with House Brackmann scale grade 4. Patients who had autoimmune disorders, psychiatric disorders, tumors, other neurological diseases, upper motor neuron lesions, stroke, recent head injury, metal/ dental implants and pregnant women were excluded.

The outcome measures were assessed on day one and at the end of 3^rd week.

A six-point House-Brackmann scale was used to evaluate tone, symmetry, positions at rest, motion of the forehead, eye and mouth and synkinesis of the face.^12,13

The severity of disability was evaluated by rating each item on a 6-point scale in the Facial Disability Index questionnaire with 10 items (5 items – Physical function & 5 items – Social function) and two subscale scores.¹⁴

A self-assessment Quality of Life questionnaire, the Facial Clinimetric Evaluation scale comprising of 15 questions based on a 5-point Likert-scale was used to evaluate the intensity and frequency of physical and psychosocial impairments of facial function in six domains. Transformed total and domain scores were calculated from 0 (worst) to 100 (best) scale.^15,16

Intervention

In Group A (Proprioceptive Neuromuscular Facilitation), bilateral movements (both sides of the face together) were used with timing for emphasis method. This was performed by preventing full motion of muscles of facial expressions such as Epicranius (Frontalis), Corrugator supercilii, Orbicularis Oculi, Risorius, Orbicularis Oris and Mentalis on the stronger side.

In Group B (Facial Motor Imagery), first person and third person motor imagery was advised. The patient was made to sit on a chair with all the muscles completely relaxed and eyes closed. The physiotherapist instructed the patients to close their eyes and imagine the actions according to the audio cues given for facial expression.

Prior to the intervention, the patients in both the groups were given interrupted galvanic current electrical stimulation to the facial expression muscles and after the intervention, the patients were asked to perform the facial expression exercises.

The treatment lasted for about 45 minutes per session, four sessions in a week for three weeks. Adverse events were not noted during the intervention. Figure 1 shows the flow of the protocols followed in the study.

Results

The baseline characteristics of Group A and B remained same i.e, the HB grade was IV on the day prior to the intervention.

The analysis of all the parameters changed significantly in both the groups. The functional analysis of facial muscle function was evaluated using House-Brackmann Scale. The results showed a difference of 2.48 (p=<0.001) in group A and a difference of 1.52 (p=0.001) in group B. PNF group showed better recovery from grade IV to I in HB Scale (Figure 2).

Facial Disability Index was used to evaluate impairment and disability of the face. Physical and social functions in group A showed more significant difference of 51.90 (p=<0.001) and 39.43 (p=<0.001) respectively. Whereas, group B showed a difference of 38.24 (p=<0.001) and 20.71 (p=<0.001) in physical and social functions respectively (Figure 3a & 3b).

Quality of life was assessed using Facial-Clinimetric Evaluation scale in which the difference in group A had greater significance than group B, 34.76 (p=<0.001) and 21.43 (p=<0.001) respectively (Figure 4).

The results for comparison between the groups has been listed in table 1.

The data is normally distributed. The analysis of differences in parameters in each treatment groups (proprioceptive neuromuscular facilitation and facial motor imagery) was done by Chi-Square or Fisher exact test. Student t test has been used to find the significance of study parameters on continuous scale between two groups (Inter group analysis) on metric parameters. Leven`s test for homogeneity of variance has been performed to assess the homogeneity of variance. Paired t-test was used to compare the means of two groups. The clinical significance was seen at 95% confidence interval.

Discussion

Bell’s palsy is a lower motor neuron disorder which can cause facial disability and impairment leading to limitations in social functions.

The main hypothesis in our study was that PNF and FMI helps to improve facial nerve function. As a result of observations and analyses, both the groups showed improvements in strength and motor function of facial muscles. In facial PNF group, statistically significant changes were seen in the assessment of facial nerve function compared to that of facial MI group.

Barbra M et al., proved the efficacy of PNF in improving facial nerve function in patients with Bell’s palsy. The findings of their randomized trial showed better and faster recovery with Kabat’s rehabilitation. Improvement in HB grade obtained in the PNF rehab patients was significantly better than that in the non-rehab group.¹⁰

A randomized controlled trial by Kumar A et al., concluded that implementing PNF can reduce facial disability and improve facial function.¹⁷

Significant improvement was noticed in facial symmetry after PNF in patients with Bell’s palsy (HB V).¹⁸

Paolucci T, stated in her commentary that motor imagery is a neuro-cognitive approach which included cognitive processes such as attention, perception, memory, imagery, language and learning skills. These were found to be activated in the process of motor imagery. In addition to this, as the patient is not required to even tense the muscles while performing motor imagery, it helped in avoiding synkinesis and improved the quality of the treatment.¹⁹ Ciriello M in his case report has observed that facial motor imagery enhanced quality of movements and limited the appearance of synkinesis and spasm in a patient with Bell’s palsy (HB III).²⁰

The present study aimed at comparing the effectiveness of proprioceptive neuromuscular facilitation versus facial motor imagery techniques in addition to electrical muscle stimulation and facial expression exercises in patients with Bell’s palsy.

Proprioceptive Neuromuscular Facilitation facilitated the voluntary response of the impaired muscles of the face. This technique provided harmony, coordination and optimal strength of the movements. Significant change was observed in improvement of facial function and reduction in facial disability.

Motor imagery improved facial motor performance and social function. This method of treatment also helped in reducing synkinesis and muscle spasm.

Results quite similar to those obtained in the present study were reported by Kumar A et al. They applied PNF 6 days weekly for 4 weeks and compared its effects.¹⁷

Proprioceptive   neuromuscular    facilitation    and facial motor imagery techniques showed significant improvement in strength and motor function of facial muscles. However, better results were seen in PNF group than in motor imagery group.

Limited cognitive ability or a dense weakness due to BP were the factors leading to difficulty in implementation of the intervention. We did not have the possibility to control the patients’ emotions in an appropriate way related to BP.

In this study, sample size calculator formula was used to estimate the sample size. The sample size, to some extent, differed from previous studies owing to the difficulty in procuring the data due to the pandemic situation. This may be one of the reasons affecting the data analysis of the current study. Therefore, it might be necessary to increase the sample size in future studies.

However, we would like to emphasize that the comparison and equalization of results of Facial PNF and Facial MI in relation to the duration of BP or ultimate recovery is vague. Hence future research studies should be conducted with the positive or negative effect that can be implemented to exemplify the clinical strategy.

Conclusion

This is the first study in which the effect of Proprioceptive neuromuscular facilitation was compared with the effect of motor imagery in Bell’s palsy. The findings of this study illustrated that PNF technique improved voluntary movements and symmetry and motor imagery avoided the appearance of synkinesis and spasm. Although there were significant improvements noticed in both the groups, PNF had better effects compared to motor imagery.