NEUROLOGY,  NEUROPATHY

Bells palsy


Idiopathic Lower Motor Neurone Facial Palsy

Acute, unilateral lower motor neuron (LMN) facial nerve (CN VII) weakness of unknown cause. Suspected viral-mediated inflammation (e.g. HSV or VZV reactivation).


Facial Nerve Anatomy & Function

  • Motor: Muscles of facial expression, stapedius, posterior digastric, and stylohyoid.
  • Parasympathetic: Lacrimal gland, submandibular and sublingual glands.
  • Sensory: Taste (anterior two-thirds of tongue), somatic sensation from posterior external auditory canal and tympanic membrane.

Risk Factors

  • Pregnancy, especially third trimester
  • Pre-eclampsia
  • Obesity
  • Diabetes mellitus
  • Hypertension
  • Recent URTI or viral illness

Clinical Features

Onset

  • Rapid onset over hours (not stroke-like); typically unilateral.

Facial Signs

  • Inability to raise eyebrow or wrinkle forehead (LMN pattern)
  • Loss of nasolabial fold, drooping of mouth
  • Inability to purse lips, whistle, or puff cheeks
  • Excessive drooling
  • Altered taste sensation (anterior 2/3 tongue)

Eye Involvement

  • Lagophthalmos (incomplete eyelid closure)
  • Dry eye due to impaired lacrimation
  • Epiphora (excessive tearing from poor eyelid tone)
  • Corneal exposure → risk of keratitis, ulceration

Ear

  • Hyperacusis (due to stapedius weakness)

Upper vs Lower Motor Neuron Facial Palsy

FeatureLMN (e.g. Bell’s palsy)UMN (e.g. stroke)
Forehead involvementYesNo (forehead spared)
LateralityUnilateralOften contralateral
Other CNS signsAbsentMay be present

Red Flags (Suggest Alternate Diagnoses)

  • Progressive or recurrent symptoms
  • Bilateral facial palsy
  • Systemic symptoms (fever, rash, arthralgia)
  • Diplopia, dysphagia, vertigo, or numbness
  • History of malignancy, head trauma, tick bite
  • Parotid or cutaneous facial masses

Differential Diagnosis

Peripheral Causes

  • Ramsay Hunt Syndrome (HZV oticus): Ear or oropharyngeal vesicles, severe pain, CN VIII involvement
  • Otitis media: Conductive hearing loss, ear pain
  • Lyme disease: Tick exposure, rash, bilateral palsy
  • Sarcoidosis: Recurrent or bilateral palsy, parotid enlargement
  • Guillain–Barré syndrome: Bilateral, ascending weakness
  • HIV infection: Consider in bilateral or recurrent palsy
  • Tumours: Parotid, temporal bone, cerebellopontine angle

Central Causes

  • Stroke: Forehead sparing, acute onset with other deficits
  • Multiple sclerosis: Painless, young adult, spontaneous recovery
  • Brain tumours/metastases: Gradual onset, raised ICP signs

Clinical Assessment

  • Differentiate LMN vs UMN
  • Examine all cranial nerves
  • Inspect ear canal and tympanic membrane (look for vesicles)
  • Oropharyngeal exam for parotid mass (tonsillar asymmetry)
  • Neurological exam: cerebellar signs, brainstem features
  • Skin: look for rash (erythema migrans – Lyme, zoster)

Management

First-line Therapy

  • Corticosteroids: Start within 72 hours
    • eTG: Prednisone 1 mg/kg (max 75 mg) orally daily for 5 days; taper over next 5 days if desired
  • Eye protection:
    • Artificial tears and ointment
    • Sunglasses for protection
    • Eyelid taping at night
    • Refer to ophthalmology if exposure keratitis

⚠️ Antivirals

  • Valaciclovir 1000 mg TDS x 7 days may have benefit when combined with steroids
  • Indicated in: Suspected Ramsay Hunt syndrome or severe cases
  • Not routinely used for isolated Bell’s palsy

⚕️ Supportive Care

  • Referral:
    • No recovery at 3 months
    • Atypical or progressive features
    • Ophthalmologic complications
    • Suspected malignancy or CNS involvement
  • Psychosocial:
    • Facial asymmetry can impact self-esteem and mental health
    • Offer psychological support or counselling as needed

Prognosis

  • 70% show improvement within 3 weeks
  • Complete recovery in 3–6 months in most
  • Worse prognosis if: complete paralysis at onset, age >60, hyperacusis, taste loss, Ramsay Hunt syndrome

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