Does electrical stimulation still have a place in the treatment armamentarium for Bell’s palsy?

KEYWORDS:

• Facial paralysis
• Bell’s palsy
• electrical stimulation
• muscle stimulation
• synkinesis

1. Introduction

Bell’s palsy, an idiopathic facial paralysis associated with peripheral facial (CN VII) nerve dysfunction, is the most common cause of facial paresis or paralysis. It is estimated that one in 60 people will be affected by Bell’s palsy in their lifetime. The unilateral partial to complete loss of motor control associated with Bell’s palsy results in ipsilateral facial drooping, a distorted appearance, inability to form desired facial expressions, difficulty articulating speech, drooling and difficulty eating, as well as incomplete eye closure and eye dryness that can lead to eye infections, corneal scarring and even permanent vision loss. Bell’s palsy can also lead to depression, social anxiety, and isolation [1].

Although recovery from Bell’s palsy generally takes from a few weeks to six months, a minority of patients with Bell’s palsy have life-long sequelae or never fully recover. Current research suggests that up to approximately two-thirds of people with Bell’s palsy recover fully within 3 months from onset without any treatment [2], and over 80% recover fully, or close to fully, with standard of care treatment with oral corticosteroids started within 3 days of symptom onset [3,4]. Oral antivirals, physical therapy exercises and massage may offer further benefit. Even with these interventions, recovery from Bell’s palsy is not always satisfactory. Rates and severity of complications of Bell’s palsy are understudied; 20% is the most commonly accepted rate of residual weakness and synkinesis [2,5]. More recent research reports that up to 45% of patients have some sequelae after Bell’s palsy, although these may be mild [5]. Older people and those with diabetes, obesity, hypertension, complete paralysis (particularly lasting more than 3 weeks) or with evidence of axonotmesis on nerve conduction studies or pathologic spontaneous activity with needle electromyography, are at elevated risk of poor outcome [6]. In addition, Bell’s palsy during late pregnancy and early puerperium particularly with severe preeclampsia, has a poor prognosis. Common sequelae of incomplete recovery from Bell’s palsy are residual weakness, contractures, and synkinesis.

Electrical stimulation, also known as electrotherapy, usually applied by a physical therapist or by the patient themselves after instruction by a physical therapist, is used and recommended by some to improve recovery from Bell’s palsy. Electrical stimulation is thought to be helpful because, with appropriate parameters, it may promote nerve recovery and produce contractions of enervated and denervated muscles to enhance motor control and prevent muscle atrophy. Muscle contractions can be produced in innervated muscles using a transcutaneously applied electrical current with a pulse duration of around 100–300 microseconds. In contrast, a continuous electrical current or a pulsed current with a pulse duration of at least 10 milliseconds, is required to produce contractions in denervated muscles. To minimize stimulation of sensory and motor nerves in the area, and associated discomfort and co-contraction of nearby muscles, triangular or exponential pulses are often used to stimulate contractions in denervated muscles. There is substantial evidence that electrically stimulated muscle contractions accelerate functional recovery after musculoskeletal surgery such as anterior cruciate ligament repair or total knee arthroplasty [7] as well as after central nervous system (CNS) injury such as stroke or spinal cord injury [8]. While the mechanisms for these clinical benefits are not fully understood, retardation of muscle atrophy, accelerated reinnervation and improved axonal regeneration are likely [9,10].

Although there is evidence supporting the efficacy of electrical stimulation for treating patients with facial palsy [11–14] and this intervention is covered by most payers, the use of electrical stimulation for patients with Bell’s palsy has been, and continues to be, controversial.

Our previously published study found that most, but far from all, physical therapists who treat patients with facial palsy use electrical stimulation in these patients [15]. The proven retardation of disuse muscle atrophy and acceleration of recovery of function associated with electrical stimulation provide a strong theoretical basis for using electrical stimulation to accelerate and optimize recovery from Bell’s palsy [7–10]. In addition, a number of trials have demonstrated benefits, including improved and accelerated recovery of functional facial movements as well as electrophysiological outcomes (including increased action potential amplitude and reduced motor nerve latency) compared to standard physical therapy without electrical stimulation or to oral prednisone [12,13,16]. Although differences in final outcomes between groups treated with or without electrical stimulation in clinical trials are modest, the approximately 30–50% reduction in recovery time associated with electrical stimulation can be clinically meaningful for many people [12,16]. Furthermore, interventions that improve recovery are needed for those with known poor prognosis at onset of paralysis, for those who do not or cannot receive steroids within the recommended 3-day window from onset, and for the at least 20% of patients who do not recover fully at three months even with steroid treatment [2,6,17].

There are also arguments for not using electrical stimulation in patients with Bell’s palsy. The strongest argument against the use of electrical stimulation for these patients is that the current supporting evidence is too flawed. The trials where benefits have been found have limitations [13,16,18–20]. The sample sizes and effect sizes are small and participants were generally not blinded to group assignment. In addition, there are negative trials where electrical stimulation was not found to be associated with clinical benefits, although none of these have found electrical stimulation to be harmful [18,21]. Clinicians discouraging electrical stimulation cite concern for worse outcomes based on their observational experience and early studies using animal models of nerve regeneration [22,23]. In addition, the results of one clinical study have been interpreted to be suggestive of electrical stimulation increasing the risk for synkinesis [14]. In this study, two of 30 participants in the electrical stimulation group developed mild synkinesis when this did not occur in any of the 30 participants in the group that did not receive electrical stimulation. The mild synkinesis observed in the two treated participants was likely due to chance and was so mild it received a score of zero on the outcome measure used in the study, the Facial Grading Scale, and thus the difference in synkinesis between groups did not reach statistical significance. While electric stimulation to the face is generally well-tolerated, it does have short-term risks and costs. Some people find the stimulation uncomfortable or painful, and the treatment requires additional time, equipment, and expertise, resulting in additional short-term costs and burden to patients and the healthcare system. The most recent Cochrane review on the physical therapy for Bell’s palsy published in 2011 included four studies where electrical stimulation was used. The authors concluded that, even though the available clinical trials do not suggest harm, higher quality studies are needed to make further recommendations on the effectiveness of electrical stimulation in the treatment of facial paralysis [24]. A more recent systematic review with metanalysis published in 2017 included five studies, three of which found improvements with electrical stimulation and two of which did not [11]. Extrapolation of these study results to clinical practice is limited by differences in protocols among studies. Protocols differ in their inclusion and exclusion criteria, the timing of treatment relative to symptom onset, electrical stimulation parameters and treatment frequency, concurrent therapies, comparison groups, and the type and timing of outcome measures.

2. Expert opinion

Today, there is equipoise regarding the use of electrical stimulation in the treatment of people with Bell’s palsy. But, given that factors known at the onset of paralysis can identify patients at risk for poor recovery, and there being no convincing evidence for long-term harms from electrical stimulation, we recommend that electrical stimulation be considered for certain patients to optimize their rate and probability of recovery. Specifically, we recommend consideration of electrical stimulation for the elderly, and those who are pregnant, have diabetes, obesity, hypertension, complete paralysis lasting more than 3 weeks, or evidence of axonotmesis on nerve conduction studies or pathologic spontaneous activity with needle electromyography. We also recommend further larger scale trials that are adequately powered to address study aims. Such studies should compare electrical stimulation, using monophasic pulsed exponential waveforms, to control interventions that control for time and attention and, to the degree possible, for the sensation and effort of electrical stimulation. Participants and outcome assessors should be blinded to group allocation, and sensitive outcome measures should be used. In addition, outcomes should be evaluated frequently during the first 3 months after symptom onset to capture rate of recovery, and also at least 6 months, and ideally 12 months, from symptom onset to capture synkinesis which typically develops in this time frame. We also suggest that future studies focus on those with a priori poor prognosis. Clinically, the use of electrical stimulation should be considered for people for whom shortening the duration of facial paralysis by a few weeks is worth the cost and effort. Electrical stimulation may also be considered for those with a priori poor prognosis who are willing to try this intervention and where it is available. Patients should be counseled that, although electrical stimulation has not been found to be harmful, benefits are uncertain.

Declaration of interest

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Additional information

Funding

This paper was not funded.