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Bell Palsy: A Specific Type of Facial Nerve Palsy

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It is important to distinguish Bell palsy from other forms of facial nerve palsy. The reasons are the difference in its treatment and its prognosis.

The term is synonymous with Bell’s palsy. In recent years though, the health care academic and scientific communities have preferred to call it Bell palsy. The name is after Sir Charles Bell who was the first person to describe the anatomy of the facial nerve in 1821.

Bell palsy occurs in 20 out of 100,000 people each year. It affects people of any age but is slightly more common after the age of 40.  Its incidence is equal in both sexes and in various ethnic groups. Diabetes, hypertension and obesity are risk factors for its occurrence.

Palsy Definition    

The word palsy is a synonym for paralysis – the total or partial loss of the ability to voluntarily move a part of the body such as a limb. The impaired movement is due to a lack of muscle contraction. In the case of facial nerve palsy it is the muscles of facial expression that are involved.

What Is Bell Palsy?  

Bell palsy is a specific type of facial nerve palsy. Unlike many of the other types, its cause is unknown. It is a peripheral neuropathy of the 7th cranial nerve on one side of the face.  Distinguishing it from other types is important though with regard to treatment and prognosis.  

It is a benign condition that usually subsides spontaneously within 3 weeks, even when not treated. Research has shown though that recovery is faster when treated with corticosteroids within 72 hours of its onset. 

Facial Nerve Function

The diagnosis of Bell palsy rests on signs and symptoms of facial nerve dysfunction. Recognition of those findings entails knowledge of the structure and functions of the nerve.   facial nerve function

The facial nerve is a mixed nerve consisting of efferent and sensory fibers.  There are 5 major branches of motor fibers which control the muscles of facial expression. They connect to muscles from the forehead down to the chin and adjacent neck. Additionally, a small branch goes to a muscle that dampens the vibrations of the small bone in the middle ear that is involved in hearing. In doing so it regulates one’s sensitivity to sound. The nerve also consists of autonomic fibers which control the secretion of tear ducts of the eyes and some of the salivary glands in the floor of the mouth.  As such, they are parasympathetic efferent nerve fibers. Sensory fibers provide taste to the anterior two thirds of the tongue and feeling in and behind the ear. The actual nerve fibers involved and the magnitude of their dysfunction are what determine the signs and symptoms of Bell’s palsy from one person to the next.

Signs and Symptoms of Bell’s Palsy

The signs and symptoms of Bell’s palsy are usually on only one side of the face and sudden in their onset.  They bell palsyare also ipsilateral – on the same side of the face – as the involved nerve. In keeping with the functions and anatomy of the facial nerve, common signs and symptoms of Bell’s palsy are the following:

  • total or partial inability to raise the eyebrow and cause wrinkling of the forehead on the affected side of the face
  • total or partial inability to close the eyelids or keep them closed against resistance on the affected side of the face
  • flattening of the junction between the nose and cheek – nasolabial fold – on the affected side of the face
  • pain in or around the ear on the affected side
  • drooping of the corner of the mouth, particularly on smiling or grimacing, on the affected side
  • absent or reduced ability to purse the lips
  • absent or reduced ability to puff out the cheeks
  • drooling
  • increased sensitivity to sound
  • changes in taste
  • dry eye on the affected side
  • dry mouth
  • paresthesias over the face

Paresthesias don’t fly in the face of the fact that the facial nerve is not the conveyor of general sensation to the face; cranial nerve V is. Rather, in the setting of Bell’s palsy this symptom a sometimes a misconstrued motor symptom.

Distinction from Other Forms of Facial Nerve Palsy

There are other forms of facial nerve palsy that warrant differentiating from Bell palsy. One that is very important in this regard is central facial nerve palsy. 

Central facial nerve palsy

Voluntary movement of muscles of facial expression requires not only a normal functioning 7th cranial nerve. Its facial nerve palsylower motor neurons in the pons of the brain stem must have connections to the axons of their respective upper motor neurons in the cortex of the brain. Those connections to the branch of the nerve which supplies the muscles of the forehead are from both sides of the brain. Thus, when 7th cranial nerve palsy is due to a brain lesion one can still wrinkle the forehead by raising the eyebrows.  The reason is even though some of the contralateral connections are missing there are still some ipsilateral ones. 

Another name for central 7th nerve palsy is upper motor neuron facial nerve palsy.  The most common causes of this type of facial nerve palsy are the following:

Other features that distinguish central facial nerve palsy from Bell palsy are the following:

  • the presence of upper motor neuron signs and symptoms in other parts of the body than the face
  • the gradualness of onset of symptoms
  • contralateral signs and symptoms (on the opposite side of where the brain lesion is)

Other forms of peripheral facial palsy

There are other non-brain causes of dysfunction of the facial nerve. They include the following:

Their respective signs and symptoms in other parts of the body and/or tests results help distinguish these conditions from true Bell palsy.

Bell Palsy Concluding Remarks

Bell palsy is a troubling but benign disorder of the 7th cranial nerve.  Its cause is unknown.  It is the most common cause of facial paralysis. It is often mistaken for a stroke and vice versa. The distribution of signs and symptoms of Bell palsy is the main clue for distinguishing it from central facial nerve dysfunction.  It is also the basis of the ironic truth; Paralysis of one side of the face in general, has a better prognosis if it involves the upper and lower face as opposed to just the lower face.



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