Bell’s Palsy: An Overview

Brendan Leng Yong Ji

Introduction

Bell’s Palsy is a unilateral lower motor neuron facial nerve paralysis of unknown cause. It is the most common cause of acute unilateral facial paralysis and a condition many medical practitioners will encounter throughout their working career (1). With respect to Ophthalmology, paralysis of the orbicularis oculi exposes the eye to significant pathology which will usually require Ophthalmic input to manage and reduce the risk of adverse long-term sequelae.

Epidemiology

Bell’s Palsy accounts for 8 out of 10 facial mononeuropathies and has an incidence of around 20-30 per 100,000 people (2-3). An average GP will see 2 cases of Bell’s Palsy in a year (4). The peak incidence is around 30-45 years of age and there is no obvious gender association (5). Risk factors associated with this disease include pregnancy, diabetes, hypertension, obesity and upper respiratory conditions (3).

Mechanism and Etiology

Bell’s is an idiopathic condition, however several theories regarding the potential mechanism has been proposed. Some have proposed that Bell’s Palsy is an autoimmune inflammatory demyelinating disease, a mononeuritis variant of Guillain-Barré syndrome (6). Another popular theory is vasospasm of any vessel along the facial nerve branch, particularly within the epineurium of the bony facial canal, causing compression of the nerve (7). Research by Murakami et al has also proposed herpes simplex virus type-1 as a major etiologic agent of the development of Bell’s Palsy with viral genome being detected using southern blot analysis in patients with Bell’s Palsy (8).

Clinical Presentation

The classical presentation of Bell’s is an onset of unilateral facial weakness or paralysis over one to three days. There will be loss of facial creases including the forehead and nasolabial fold (Figure 1).

Bellspalsy
Figure 1: Loss of facial creases of forehead and nasolabial fold seen in Bell’s Palsy (Image courtesy of James Heilman, MD, CC BY-SA 3.0, via Wikimedia Commons)

Involvement of the greater petrosal nerve or chorda tympani could result in decrease in tear production or diminished taste. Loss of orbicularis oculi innervation results in exposure of the eye and resultant epiphora. Attempted eye closure will result in upturning of the eye termed Bell’s Phenomenon. Patient’s may complain of numbness, but objective testing of sensation is normal (9).

A thorough history and examination should be conducted as there are many differentials of a facial nerve palsy. Alternative diagnoses should be considered if there is mention of a rash, weight loss, other neurological deficits, trauma, or a history of systemic medical conditions such as sarcoid of multiple sclerosis (10).

Essential examinations for assessing the patient with facial palsy include: (11)

• Otoscopy for possible vesicular lesions

• Head and neck for skin lesions or palpable masses

• Full neurological exam, with particular focus on cranial nerves, for any other neurology or forehead sparing

• House-brackmann grading to assess degree of palsy and record clinical improvement or progression (12)

Specifically for Ophthalmology, the following workups are also essential (13)

• Ophthalmic exam including visual acuity, eye and pupillary movements

• Lids and adnexa for eyebrow position and movement, frontalis function, orbicularis oculi function, lagophthalmos, ectropion and palpebral fissure width

• Cornea for corneal defects, ulcers, thinning, neovascularization, or loss of corneal reflex

• Conjunctiva for any chemosis or hyperaemia

Investigations

Bell’s palsy is a clinical diagnosis and routine investigations is not always required. However, additional signs and symptoms that could indicate an underlying pathology could warrant further investigation. The following investigations can be considered to support the diagnosis of facial palsy (14-15).

• Full blood count to rule out leukaemia in children with recurrent facial palsy

• Serology to identify infectious pathology

• Radiological imaging to identify potential intracranial pathology or mass lesions

• Audiogram if there is suspicion of hearing involvement

Treatment

The mainstay of treatment for Bell’s Palsy is medical with the use of a high dose steroid regime which shows significant benefit to the prognosis of patients (9-11, 16). In ophthalmology, the primary aim of management is the prevention of exposure keratopathy to ensure good long term visual outcome. This is usually achieved with artificial tears throughout the day and lubricating gels at night. Patient’s with lagophthalmos will also benefit from taping their lids shut at night. Conservative management is efficacious in majority of patients. However, in the minority that fail to respond, transconjunctival botulinum toxin injection can help. This aim is to weaken the levator palepbrae superioris muscle, causing ptosis and hence protecting the cornea.

If there is chronic lagophthalmos with minimal prognostic improvement, surgical intervention may be indicated. Some potential surgical options include the following (17):

• Gold or platinum implantation in the upper lid to assist with eye closure

• Mullerectomy and levator recession for upper lid ectropion• Tarsorrhaphy can provide temporary or permanent corneal protection but may not be aesthetically acceptable

Conclusion

Bell’s Palsy is a common condition that can have potentially devastating ocular sequelae. This is a condition that will usually require input from several specialties, including ENT and ophthalmology. Good understanding and documentation of the examination findings is vital in the differential diagnosis and monitoring of this disease. It is vital patients receive appropriate eye care advice and intervention to prevent the development of exposure keratopathy.

References

  1. Warner MJ, Hutchison J, Varacallo M. Bell Palsy. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482290/
  2. Loukas M. The neurologist’s dilemma: A comprehensive clinical review of Bell’s palsy, with emphasis on current management trends. Medical Science Monitor. 2014;20:83-90.
  3. Baugh R, Basura G, Ishii L, Schwartz S, Drumheller C, Burkholder R et al. Clinical Practice Guideline. Otolaryngology–Head and Neck Surgery. 2013;149(3_suppl):S1-S27.
  4. Glass G, Tzafetta K. Optimising treatment of Bell’s Palsy in primary care: the need for early appropriate referral. British Journal of General Practice. 2014;64(629):e807-e809.
  5. Marson A. Bell’s palsy. Western Journal of Medicine. 2000;173(4):266-268.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1071111/
  6. Greco A, Gallo A, Fusconi M, Marinelli C, Macri G, de Vincentiis M. Bell’s palsy and autoimmunity. Autoimmunity Reviews. 2012;12(2):323-328.https://pubmed.ncbi.nlm.nih.gov/22684016/
  7. Gussen R. Pathogenesis of Bell’s Palsy. Annals of Otology, Rhinology & Laryngology. 1977;86(4):549-558.https://pubmed.ncbi.nlm.nih.gov/889228/
  8. Murakami S. Bell Palsy and Herpes Simplex Virus: Identification of Viral DNA in Endoneurial Fluid and Muscle. Annals of Internal Medicine. 1996;124(1_Part_1):27.https://pubmed.ncbi.nlm.nih.gov/7503474/
  9. Tiemstra J, Khatkhate N. Bell’s palsy: diagnosis and management. Am Fam Physician. 2007;76(7):997-1002.https://www.aafp.org/afp/2007/1001/p997.html
  10. Rahman I, Sadiq S. Ophthalmic Management of Facial Nerve Palsy: A Review. Survey of a Ophthalmology. 2007; 52(2):121-144.
  11. Wallwork B, Panizza B, Phan N. A general practice approach to Bell’s palsy. Australian Family Physician. 2016;45(11).https://www.racgp.org.au/afp/2016/november/a-general-practice-approach-to-bell%E2%80%99s-palsy/
  12. House JW, Brackmann DE. Facial nerve grading system. Otolaryngol Head Neck Surg 1985;93(2):146–47
  13. Sohrab M, Abugo U, Grant M, Merbs S. Management of the Eye in Facial Paralysis. Facial Plastic Surgery. 2015;31:140–144.
  14. RIORDAN M. Investigation and treatment of facial paralysis. Archives of Disease in Childhood. 2001;84(4):286-288.https://adc.bmj.com/content/84/4/286
  15. Baugh et al. Clinical Practice Guideline: Bell’s Palsy. Otolaryngology- Head and Neck Surgery. 2013; 149(3S); S1-S27.
  16. Madhok V, Gagyor I, Daly F, Somasundara D, Sullivan M, Gammie F et al. Corticosteroids for Bell’s palsy (idiopathic facial paralysis). Cochrane Database of Systematic Reviews. 2016;2016(7).https://pubmed.ncbi.nlm.nih.gov/27428352/
  17. Lee V, Currie Z, Collin J. Ophthalmic management of facial nerve palsy. Eye. 2004;18(12):1225-1234. https://pubmed.ncbi.nlm.nih.gov/15094735/
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