Definition and Overview
Facial nerve palsy, especially idiopathic facial nerve palsy, is called Bell's palsy. It is a disease in which motor paralysis on one side of the face suddenly occurs due to acute inflammation and edema of the 7th cranial nerve (facial nerve).
The annual incidence is approximately 15 to 30 per 100,000 population, making it the most common cause of unilateral facial paralysis. It can occur at any age, but is more common between the ages of 15 and 45, and the risk of occurrence increases in pregnant women and diabetic patients.
Causes and Pathophysiology
Reactivation of herpes simplex virus type 1 (HSV-1) after latency in the ganglia is known to be the most likely cause. As the reactivated virus moves along the facial nerve, it causes inflammation and swelling within the nerve, and the nerve is compressed within the narrow facial canal, resulting in paralysis.
Other causes include Ramsay Hunt syndrome caused by the varicella zoster virus (VZV), Lyme disease, and otitis media, which are secondary facial paralysis that are distinct from Bell's palsy.
symptoms
The typical symptom is loss of motor function of the entire face on one side, with the following findings:
- Disappearance of forehead wrinkles and inability to raise the forehead
- Inability to close eyes completely (lagophthalmos), tearing
- Sagging mouth corners, food leakage
- Postauricular (behind the ear) pain: Often precedes paralysis 1-2 days before onset.
- Decreased sense of taste (anterior two-thirds of tongue)
- Hyperacusis: When the stapedius muscle is paralyzed.
Symptoms progress over several hours to several days, and most cases reach maximum paralysis within 72 hours.
diagnosis
Bell's palsy is a clinical diagnosis. It is important to check the pattern of peripheral facial paralysis of the entire face, including the forehead, and rule out secondary causes.
Differentiating it from central facial paralysis (stroke, brain tumor) is key. In central lesions, upper motor neurons in the corticospinal tract are damaged, so the forehead area is partially innervated by the contralateral brain hemisphere, and forehead wrinkles are relatively preserved. If accompanied by forehead paralysis, it suggests a peripheral lesion.
- Blood tests: blood sugar, thyroid function, CBC, etc. to rule out secondary causes
- MRI: Performed when there are atypical symptoms (bilaterality, gradual worsening, recurrence) to exclude tumors, etc.
- Nerve conduction study (NCS)/electromyography (EMG): used to evaluate the degree of nerve damage and predict prognosis
treatment
Early treatment within 72 hours of onset is critical to prognosis.
Steroids are the first-line treatment. It is recommended to administer prednisolone 1mg/kg/day (maximum 60-80mg/day) for 5-7 days and then gradually reduce the dose. The number needed to treat (NNT) was reported to be approximately 10.7.
Antiviral drugs should be considered in combination with steroids in patients with severe Bell's palsy. Acyclovir or valacyclovir are used, but the effectiveness of antiviral drugs alone is inferior to that of steroids.
Eye protection is essential if you can't close your eyes. Prevent corneal damage by wearing artificial tears, eye ointment, night patches, and protective glasses.
Physical therapy (facial muscle exercise rehabilitation) can help prevent joint movements and restore function during the recovery phase.
prognosis
Complete recovery occurs in approximately 70% of patients, and most reach maximum recovery within 3 to 6 months from the onset of the disease. The prognosis of patients with partial palsy is better than that of patients with complete paralysis.
In about 15% of cases, mild aftereffects (synkinesis, crocodile tear syndrome) may remain, and in about 5% of cases, severe aftereffects persist. The recurrence rate is approximately 7-10%, and additional evaluation for secondary causes is necessary when recurrence occurs.
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This information is provided for medical educational purposes and is not a substitute for individual medical care or treatment. If you have any symptoms, be sure to seek professional advice. Inquiries: Osang Neurosurgery 1599-5453 | osns.co.kr