Bell’s palsy is an idiopathic palsy of the facial nerve (cranial nerve VII)1-3 that affects approximately 30 individuals per 100,000.1-5 Considered the most common disorder affecting the facial nerve, most clinicians believe that Bell’s palsy is caused by inflammation of the geniculate ganglion within the facial canal, between the labyrinthine and the tympanic segments, leading to compression, ischemia and demyelination.2 Given the function of the facial nerve, Bell’s palsy can negatively impact the muscles of facial expression, sensation to the anterior two thirds of the tongue and the parasympathetic outflow to the lacrimal and salivary glands.2 Clinically, patients with Bell’s palsy present with weakness and/or paralysis on one side of the face with eye irritation and drooling secondary to loss of eyelid and mouth control, respectively.2 Moreover, when patients attempt to close their eye on the affected side, their lower eyelid typically droops and the eye rolls superiorly (the clinical sign commonly referred to as Bell’s phenomenon).2
For many years, physical therapists and medical physicians have longed to understand the etiology of Bell’s palsy so as to provide an optimal management strategy. While the literature suggests that a number of pathological factors are likely responsible for the initial inflammation of the facial nerve, the etiology and pathophysiology of the condition continues to be a topic of debate among researchers and clinicians.3 That is, while some researchers have proposed that Bell’s Palsy may be initiated by diabetes myelitis, hypertension or viral infection (specifically, herpes simplex and herpes zoster strands), others have noted a strong correlation between Bell’s Palsy and rheumatic factors and also pregnancy.1, 4, 6, 7
Regardless of etiology, 80-85% of those effected by Bell’s palsy experience symptom resolution within 3 weeks, and the remaining 10-15% of cases resolve in less than 6 months.4 Although corticosteroids have traditionally been prescribed to combat facial nerve inflammation, a Cochrane review by Salinas et al. reported no significant functional improvement in patients treated with prednisone compared to placebo at 6 months.2, 8 Pietersen further cited ethical considerations of using corticosteroids, particularly prednisone, to treat Bell’s palsy, as “…no evidence of its efficacy exists…”4 In contrast, acyclovir, an antiviral pharmaceutical, has been reported to have superior effects in treating Bell’s palsy compared to prednisone.9 However, a Cochrane review by Allen and Dunn found no advantage of using antiviral drugs to treat Bell’s palsy.10 In fact, a number of studies found that acyclovir, given in conjunction with prednisone, or given independently, resulted in no benefit for the treatment of Bell’s Palsy.11-14
A systematic review by Holland et al. concluded that, “several physical therapies, including massage and facial exercises, are recommended to patients, but there are few controlled clinical trials of their effectiveness…”8 Only one study in a systematic review by Pereira found facial exercises to produce statistically significant improvements in the treatment of patients with Bell’s Palsy.15, 16 Therefore, the treatment for Bell’s Palsy remains highly anecdotal and relatively inconclusive, and the fact that most cases spontaneously resolve makes treatments for the disease particularly difficult to research.5,6
EVIDENCE FOR DRY NEEDLING AND/OR ACUPUNCTURE IN BELL’S PALSY
The terminology, philosophy and theoretical constructs differ between Western-based dry needling and traditional Chinese acupuncture. For example, according to traditional Chinese theory, “peripheral facial paralysis is caused by the attack of pathogenic wind and cold on Yangming and Shaoyang meridians, which lead to malnutrition of the muscles and the meridians.”17, 18 The malnutrition leads to facial paralysis or wry face in traditional Chinese Medicine. 17, 18 Nevertheless, the procedure of inserting monofilament needles is similar;19 therefore, the terms manual and electrical dry needling are used synonymously with manual and electroacupuncture, respectively, throughout this report to describe needling procedures that penetrate the skin in the absence of injectate.19, 20
Several Cochrane Reviews and meta-analyses have considered the use of acupuncture for Bell’s palsy but have reported inconclusive outcomes.3, 6 Notably, these conclusions were drawn not because of a lack in the number of studies published on the use of acupuncture in Bell’s palsy, but because of poor methodologic quality. Liang et al. cited hundreds of articles that have used acupuncture to treat Bell’s palsy in the last 50 years, but only 15% were randomized controlled trials or controlled trials.21, 22 While a non-systematic review of 50 studies spanning a 10-year period reported an average recovery rate of 81%23 in patients with peripheral facial nerve paralysis after receiving acupuncture, other studies have reported recovery rates as high as 95%24 and 99.9%.25,22 Notably, a number of studies have demonstrated that electroacupuncture is more effective than manual acupuncture for treating peripheral facial paralysis.22, 26-29 While the physiological mechanism in which acupuncture with and without electric stimulation leads to improvements in function continues to be a topic of debate in the literature, there is evidence to suggest that the modality decreases inflammatory factors, improves blood flow to the facial nerve, strengthens the immune system and facilitates remyelination.30, 31
ELECTROACUPUNCTURE REDUCES INFLAMMATION
According to Yilmaz et al., peripheral facial nerve palsy is accompanied by significant increases in inflammatory factors, such as TNF-α, IL-6 and IL-1β.32 However, according to a systematic review by Kavoussi and Ross, experimental evidence from both laboratory and clinical studies found that electroacupuncture inhibits the production of inflammatory cytokines, including TNF-α, IL-1β, IL-6 and IL-18.33 Peri-neural needling of the sciatic nerve with electroacupuncture has been shown to lead to increased production of dopamine in the adrenal medulla, subsequently reducing levels of TNF-α,34 which is particularly noteworthy given that TNF-α has also been linked to facial nerve demyelination.30, 33, 35-37 Evidence from the literature also suggests that electroacupuncture leads to increased levels of peripheral calcitonin gene-regulated peptide (CGRP) and substance P.38, 39 Given that substance P and CGRP are factors of inflammation, this finding is somewhat counterintuitive. However, previous studies have demonstrated that while CGRP in high concentrations causes inflammation, CGRP in low doses has the opposite effect.40-42 Electroacupuncture may simply stimulate a continuous, low-level release of CGRP and substance P over a 15-20 minute period of time that is appropriate to reduce inflammation.20 Alternatively, given that substance P and CGRP are released together during electroacupuncture, the substance P may autoregulate CGRP to levels sufficient for anti-inflammation.40 Increased levels of CGRP and substance P from electroacupuncture may also facilitate a negative feedback loop, decreasing factors of inflammation from neural sources.38
Electroacupuncture has also been shown to decrease systemic factors of inflammation by stimulating the hypothalamic-pituitary-adrenal (HPA) axis.43 The release of increased levels of cortisol (corticosterone in animals) has been shown to inhibit interleukin factors and TNF-α.44 Electroacupuncture also stimulates an increase in endogenous anandamide, which activates CB-2 receptors on both neural and non-neural cells throughout the body to inhibit the release of pro-inflammatory factors such as TNF-α, IL-4, IL-6, IL-8, and IL-10, and increase opioid production.45, 46 Given that cortisol also blocks COX-2’s ability to breakdown endogenous anandamide, the ability of electroacupuncture to stimulate the HPA axis is particularly noteworthy.44
ELECTROACUPUNCTURE IMPROVES BLOOD FLOW
The release of CGRP during electroacupuncture is also significant, as CGRP increases blood flow via vasodilation, which breaks the cycle of ischemia and contributes to tissue healing.47, 48 CGRP is recognized by receptors on vascular smooth muscle which initiates a cascade of events mediated by protein kinase A (PKA) leading to vasodilation.47 PKA also stimulates nitric oxide synthase, increasing the production of nitric oxide, thereby exaggerating the vasodilation effect.47 Previous investigations have found significant increases in tissue vasodilation following both acupuncture49 and electroacupuncture.50, 51 However, when Lazaro et al. blocked neuromuscular junctions in the target tissue with succinylcholine, a nicotinic acetylcholine receptor blocker, the increased vasodilation was lost. Since electroacupuncture has the ability to continuously stimulate neuromuscular junctions in target tissue, it may be better able to initiate vasodilation than manual acupuncture alone. In doing so, electroacupuncture may be more advantageous for nerve regeneration and healing.
Inoue et al. reported a significant increase in blood perfusion of the sciatic nerve following neural stimulation of the pudendal or the sciatic nerve in 13 Windstar rats compared to manual acupuncture with needle rotation in the lumbar paraspinal muscles.51 Interestingly, when patients with lumbar stenosis or a herniated lumbar disc were randomly assigned to receive either manual acupuncture in the lumbar paraspinals (at the level of disorder), peri-neural needling of the pudendal nerve or peri-neural needling of the sciatic nerve roots, only the group receiving electroacupuncture at the sciatic nerve roots experienced immediate and sustainable relief.51 While it would have been interesting to see if the findings of this study would have been the same in patients with sciatica, there seems to be a strong association between neural blood perfusion and clinical relief.
ELECTROACUPUNCTURE & REMYELINATION
The facial nerve is part of the peripheral nervous system, and therefore, its axons are myelinated by Schwann cells. A number of studies have demonstrated morphologic changes in Schwann cells and demyelination of the facial nerve secondary to Bell’s Palsy.52 However, to our knowledge, only one study has investigated the use of electroacupuncture to improve myelination in patients with facial nerve palsies.53 After creating a facial nerve injury in 60 rabbits, Zhang et al. found that daily sessions of electroacupuncture sessions for 3 weeks led to significant remyelination of axons and an increased number of organelles compared to the control group.53
Similarly, Liu et al. provided 20 minutes of deep electroacupuncture to the sciatic nerve at GB30 (i.e. distal/lateral piriformis) for 14 days and found more organized axons, myelin and Schwann cells, which correlated with significant improvements in nerve conduction velocity and in the amplitude of evoked potentials compared to superficial electroacupuncture and control.54 The animals receiving deep electroacupuncture also had significantly greater nerve growth factor and significantly less c-FOS immunoactivity, indicative of more efficient repair and reduction of inflammation, respectively.54 Yang et al. also investigated the use of electroacupuncture to treat the sciatic nerve in rabbits with lumbar intervertebral disc protrusions.55 Following an unspecified treatment regimen with electroacupuncture at GB30, the authors noted superior myelin repair than control and non-acupoint electroacupuncture, which correlated with improved walking ability and touch sensation scores.55 While more research is required, these studies suggest that deep electroacupuncture at acupoint locations is able to facilitate myelin repair, which may lead to more efficient recovery in patients with neural injuries, to include Bell’s palsy.
ELECTROACUPUNCTURE & IMMUNITY
Given the connection between Bell’s palsy and the herpes simplex virus (HSV), acupuncture may also provide therapeutic value by strengthening the immune system. A number of studies from the literature suggest that acupuncture is able to facilitate T lymphocyte56 and T-helper lymphocyte proliferation,57, 58 thereby stimulating cell-mediated immunity to directly combat the herpes infection and decrease the symptoms of Bell’s palsy.30 The ability of acupuncture to stimulate T-helper lymphocytes is particularly powerful as they amplify the immune response by stimulating other types of immune cells, including cytotoxic T lymphocytes, which have been shown to play a crucial role in eliminating HSV-1 infections.59
ELECTROACUPUNCTURE RECOMMENDED FOR BELL’S PALSY
A systematic review by Zheng et al. reviewed 33 studies conducted over the last 50 years in order to make recommendations on the therapeutic value of acupuncture for peripheral facial paralysis.17 While traditional Chinese acupuncturists generally consider the combination of both local (i.e. on the face) and distal points (i.e. typically hands and/or feet) as best practice for facial paralysis,17 Zheng et al. specifically recommended needling the following facial points: ST4 (i.e. the zygomaticus major/minor, orbicularis oris, risorius and buccinator), ST7 (deep masseter and lateral pterygoid), ST6 (lower border of superficial masseter), CV24, (inferior orbicularis oris), LI20 (nasalis and levator labii superioris), SI18 (in the depression below the zygoma), GB14 (frontalis), ST2 (inferior orbicularis oculi, infra orbital nerve and artery), GV26 (superior orbicularis oris), Yuyao (supra orbital nerve and artery, superior orbicularis oculi).17 The authors recommend daily acupuncture with manual or electric stimulation for 10 consecutive days followed by 2-5 days of rest.17 This regimen should be continued for 20-40 treatments in total.17
Notably, a number of studies support the use of electroacupuncture for facial nerve regeneration following trauma.22, 60, 61 According to a detailed study by Mayor, electric stimulation should be biphasic and low frequency (2-4 hertz) and dense-disperse (alternating high and low frequencies) instead of continuous.22 As the patient improves, high-frequency or intermittent stimulation may be more appropriate.22 Alternatively, the Mayor study recommends stimulation that is consistent with end plate action potentials, low variable frequency (5-8 Hz), 80 microseconds and an alternating 2 second on / 2 second off current.22, 62 Nevertheless, a more recent investigation of 119 patients will Bell’s palsy found no statistical difference in treatment outcomes when patients were given electroacupuncture with continuous, dense-disperse or intermittent waveforms.63
While electroacupuncture has been found to be more effective than manual acupuncture with a lesser number of treatments required,22, 26-29 some clinicians adamantly claim that electricity should never be used for facial paralysis, particularly during the acute stage of the condition, for fear of increasing facial nerve edema and initiating bioelectric conduction disorders.64, 65 More specifically, the stimulation of denervated muscle could result in contractures and synkinesis,66 involuntary facial movement that comes from active movement of different facial muscles or muscle groups.67 Notwithstanding these findings and claims, the use of electroacupuncture during the acute phase of Bell’s palsy has been shown to stabilize symptoms and facilitate better clinical outcomes than patients treated during subacute and chronic time periods.22, 68, 69
Therefore, instead of electroacupuncture being contraindicated during the early stages of Bell’s palsy, Mayor suggests a graded treatment strategy that is consistent with the stages of facial paralysis.22 In particular, the number of needles and intensity of treatment should be minimized during the early stage of the condition. Some authors have reported success using acupuncture during the acute phase of the condition by needling the contralateral side of the face,70 restricting needles to superficial insertion,71 providing manual stimulation instead of electric stimulation72 and restricting the intensity of electric stimulation.22, 73 For electroacupuncture, Mayor specifically recommends using “a low frequency at a low intensity (and possibly with a relatively brief pulse duration), sensory (even submotor) level first, motor level later.”22 During acute phases, 15-20 minutes of electroacupuncture is appropriate, but clinicians may work up to 20-30 minutes of treatment.22
Ironically, the most recent position statement on dry needling from the American Physical Therapy Association fails to consider peri-neural needling or needling with electric stimulation.19, 74 That is, the 2013 APTA position statement only includes “muscle” or “connective tissue” as possible targets for dry needling. Nevertheless, recent legislation on the use of dry needling by physical therapists, in both Arizona (2014) and Tennessee (2016), defined dry needling as “stimulating neural, muscular and connective tissues for the management of neuromusculoskeletal conditions.”
While a multimodal treatment strategy is likely important, the literature suggests that the use of electrical dry needling or electroacupuncture prior to facial exercises75, 76 may be effective for treating the symptoms associated with Bell’s palsy.
Dr. Clinton Serafino, DPT, Cert. SMT, Cert. DN, Dip. Osteopractic
AAMT Fellow-in-Training & Osteopractic Physical Therapist
Physical Therapy Center, Monroe, NC
Dr. Justin Loss, DPT, Cert. SMT, Cert. DN, Dip. Osteopractic
AAMT Fellow-in-Training & Osteopractic Physical Therapist
ATI Physical Therapy, Chapel Hill, NC
Dr. Raymond Butts, PhD, DPT, MSc, Cert. DN, Cert. SMT, Dip. Osteopractic, MAACP(UK)
Senior Faculty, AAMT Fellowship in Orthopaedic Manual Physical Therapy
Member, Acupuncture Association of Chartered Physiotherapists
Dr. James Dunning, DPT, MSc, MAACP (UK), FAAOMPT, Dip. Osteopractic
Director, AAMT Fellowship in Orthopaedic Manual Physical Therapy
Member, Acupuncture Association of Chartered Physiotherapists
Member, Manipulation Association of Chartered Physiotherapists
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