The facial nerve is the nerve that supplies, among other things, the mimic muscles of the face. Likewise, it is involved in the sensation of taste, in the secretion of tears and saliva, and it supplies the smallest muscle in humans, which is located in the ear, the stapedius muscle. The facial nerve is one of the 12th cranial nerves (HN), or more precisely, it is the 7th cranial nerve. Paralysis of this nerve is called facial nerve palsy (synonyms: Bell’s facial palsy; Bell’s palsy; Bell’s paralysis; Bell’s syndrome; facioplegia; facial palsy; facial nerve paralysis; facial palsy; paralysis of cranial nerve VII; paralysis of facial nerve; paresis of facial nerve; peripheral facial palsy; prosopodiplegia; prosopoplegia; central facial palsy; ICD-10: G51.0).
Symptoms – Complaints
Central facial nerve palsy is distinguished from peripheral facial nerve palsy. In central facial palsy, the forehead can still be furrowed and the eyelid can still be closed. The other symptoms are identical to those of peripheral nerve palsy. If central facial nerve palsy is present, motor supply to the forehead is preserved because exchange of nerve fibers between the nuclei is possible. If the facial nerve is peripherally paralyzed, the entire mimic musculature of the affected side fails and typical symptoms occur. The above symptoms occur depending on the localization of the nerve damage:
- Decreased secretion of tears and saliva – damage to the greater petrosal nerve and tympanic chorda (branches of the facial nerve).
- Hyperacusis – pathological fine hearing due to failure of the stapedius muscle.
- Disturbance of taste sensations in the anterior 2/3 of the tongue – due to damage to the chorda tympani.
- Unilateral flaccid paralysis of the mimic muscles.
The forehead can no longer be furrowed and eyelid closure is limited. The corners of the mouth droop, the oral fissure can be closed only weakly and not completely.
Pathogenesis (disease development) – etiology (causes)
Possible causes of central facial nerve palsy include cerebral hemorrhage or stroke (apoplexy). In about three-quarters of cases of peripheral nerve palsy, the cause is unknown – this is called idiopathic facial nerve palsy, also known as Bell’s palsy. Possible causes for the other cases of peripheral facial nerve palsy are:
- Herpes virus infections (HSV type I), causative agent of labial herpes.
- Zoster oticus (herpes zoster – infestation of the ear canal and or pinna).
- Lyme disease – infectious disease caused by the bacterium Borrelia burgdorferi; the pathogens are transmitted by ticks.
- Guillain-Barré syndrome (GBS), also called Landry-Guillain-Barré-Strohl syndrome – neurological disorder caused by polyradiculitis. It is an inflammatory disease of the nerve roots arising from the spinal cord (radiculitis) and the peripheral nerves with paralysis symptoms.
- Diphtheria – infectious disease caused by the toxin of Corynebacterium diphtheriae.
- Neoplasms (tumors) – schwannomas, meningiomas, glomus tumor, malignant (malignant) tumors of the parotid (parotid gland) or skull base tumors.
- Diabetes mellitus (diabetes).
- Pregnancy – increased risk by a factor of three, especially in the last trimester.
- Trauma – temporal bone fracture
Consequential diseases
If eyelid closure is incomplete and tear secretion is decreased, corneal ulceration may occur. In about 80 percent of cases, the paralysis regresses within a few weeks to months, but incomplete healing of the paresis is also possible. In this case, so-called crocodile tears occur with unilateral irritation of the taste buds. Furthermore, dyskinesia (disturbed movements), synkinesia (involuntary movement of muscles, e.g. eyelid closure during mouth movement) or facial contracture (constant tension of the facial muscles) may occur. Defect healing often occurs, particularly in association with zoster virus, whereas facial paresis due to Borrelia infection has a favorable prognosis.
Diagnostics
Diagnosis is based on clinical examination. Otoscopy (ear examination) must be performed to detect herpes infection, because herpes vesicles may also be present exclusively in the ear canal.Furthermore, the following are used:
- Electrophysiological studies – e.g., canalicular magnetic stimulation, electrical mastoid facial stimulation.
- Laboratory diagnostics – detection of: Borrelia, varicella zoster, herpes simplex, if necessary lumbar puncture.
Therapy
If the cause of facial nerve palsy is known, treatment consists first of all in eliminating the cause. In cases of idiopathic facial nerve palsy, cortisone therapy is administered with medication. Viral infections are treated with the help of virustatics, and bacterial infections such as Lyme disease are treated with the administration of antibiotics. In the absence of eyelid closure, artificial tears are dripped into the eye during the day, and a watch glass bandage with eye ointment is applied overnight to prevent the cornea from drying out. Synkinesia, such as involuntary eyelid closure during speech, can be treated with botulinum toxin injections. Complementary and supportive physiotherapy of the facial muscles can be performed.
