Bell’s palsy is defined as rapid onset paralysis (72 hours from first sign of weakness until complete or near-complete paralysis) of the facial musculature on one side of the face, without an apparent cause. Bell’s palsy affects all branches of the nerve, from the forehead to the neck. A viral illness preceding the paralysis, pain around and behind the ear, changes in taste, facial numbness, and tongue numbness are all commonly associated symptoms.
The cause of Bell’s palsy is uncertain, though there is strong evidence to suggest a viral cause, with most data pointing toward activation of the herpes simplex virus (HSV) that lives in the geniculate ganglion, a slight enlargement in the facial nerve. This virus infects most human beings (85-90% of the population) early in childhood, but usually lies dormant (giving no symptoms). When something triggers it, it activates to give either cold sores, or perhaps Bell’s palsy.
The fact that Bell’s palsy appears to respond to antiviral and anti-inflammatory medications further supports the relationship between HSV and Bell’s palsy.
For recurrent Bell’s Palsy, or unsatisfactory / prolonged recovery, see other options in our Interventions section.
Phases of Recovery
The recovery from Bell’s Palsy tends to follow one of two pathways. There is a set of patients in whom recovery begins within three weeks of the onset of paralysis, and who tend to recover fully. This represents roughly 85% of all Bell’s palsy patients and may be referred to as the “rapid recovery” group. A smaller set of patients experience delayed or incomplete recovery, and go on to require additional therapy in order to improve their outcome. This “delayed / partial recovery” group represents roughly 15% of all Bell's palsy patients.
Facial nerve dysfunction can be seen in patients who suffer from acute and chronic ear infections (otitis media). There are a number of ways that the facial nerve can be affected, and usually the time course of onset and the duration of the facial nerve dysfunction are indicators of the state of the nerve and the likelihood of full recovery.
Facial paralysis that occurs suddenly during an acute ear infection implies inflammation of the nerve, leading to a blockage of neural impulses (neurapraxia). This tends to occur in infants and young children, because the bony canal surrounding the nerve is not as insulated from the middle ear space as it is in adults. Ordinarily, prompt treatment of the infection, that sometimes includes putting a hole in the ear drum to remove the infected contents, leads to recovery of the nerve.
Facial paralysis or paresis (partial paralysis) immediately following ear surgery can be related to one of several things.
- The administration of local anesthetic can cause a temporary paralysis, lasting for several hours after the procedure.
- The thorough removal of all diseased tissue in middle ear and mastoid surgery can sometimes necessitate exposing a segment of the facial nerve in its bony canal. This exposure can result in temporary nerve inflammation which can lead to transient facial nerve paralysis. This type of injury generally recovers over weeks to months.
- It is possible to inadvertently nick, bruise, or divide the facial nerve during middle ear and mastoid surgery. This is characterized by immediate, complete paralysis that does not recover. If the injury was not recognized during the operation, sometimes re-exploration for assessment of the extent of injury, and possible decompression, repair, or grafting is warranted.
Sudden facial paralysis in the setting of chronic ear disease suggests damage caused by expanding chronic infection. Pressure on the nerve can occur if the disease affects and wears away bone, as is seen with cholesteatoma. When sudden facial paralysis occurs in the face of known chronic ear disease, prompt surgical exploration with evacuation of disease and nerve decompression usually results in good recovery of function.
There are several causes of congenital (present at birth) facial paralysis. They are genetic causes (predetermined in the genes), paralysis related to in utero insult, and paralysis caused by trauma during delivery.
Example of Congenital
It is important to make an effort to identify the cause of the paralysis, since management differs according to etiology.
Certain genetically determined syndromes have facial paralysis as one of their features. The most well known of these is called Mobiius Syndrome, in which there is a congenital absence of the facial nerve and/or musculature on both sides, as well as abducens nerve palsy. There is a bilateral facial paralysis and inability to move the eye(s) out to the side, with no chance of spontaneous recovery.
Goldenhar’s Syndrome refers to maldevelopment of the first and second branchial arches, leading to hemifacial microsomia and facial nerve abnormalities. Some evidence points to an early in utero insult contributing to the development of hemifacial microsomia in some cases.
When a newborn child appears to be completely normal, except a facial palsy is present at birth, the possibility of birth trauma to the nerve must be considered. Cases of facial nerve damage from skull base fractures, from forceps delivery, and from shoulder dystocia have been reported. In these situations, injuries are virtually always crush injuries rather than transection injuries, and the prognosis for spontaneous recovery is good.
Both benign and malignant tumors can arise from the facial nerve, anywhere along its course. The most common of these are geniculate ganglion hemangiomas and schwannomas, both of which are benign but can cause serious problems if untreated and allowed to enlarge sufficiently. Malignant facial nerve tumors are exceedingly rare, and can represent either primary malignancies of the nerve, or metastases from distant sites.
Facial Nerve Tumor CTs
Facial paralysis occurring after head trauma can be due to several causes. Most commonly, the temporal bone (through which the facial nerve travels) can fracture, leading to either temporary or permanent damage to the nerve. Less commonly, direct brainstem injury or stroke related to the trauma can lead to brain malfunction, so that the facial musculature does not work properly, even if the nerve itself is intact.
Temporal bone fractures are classified into either longitudinal or transverse fractures, depending on their
Transverse Bone Fracture
course through the bone. The schematic to the right illustrates the difference in direction between the two types.
Longitudinal fractures are more common, and account for 80% of all temporal bone fractures. They occur from a blow to the side of the head; the fracture line tends to run along the floor of the ear canal, can rupture the ear drum, and can result in bleeding from the ear. In only about 20% of these cases, the facial nerve is injured in its course through the temporal bone. While nerve crush or transection can occur, more commonly the etiology of the facial paralysis is swelling within the tight bony canal through which the nerve runs. Since there is no room for swelling to occur, the nerve gets "squeezed" within the facial canal, leading to nerve malfunction. In this clinical situation, usually the facial muscles are working normally right after the injury, but become weak in the ensuing several hours to days, as the swelling sets in. The best prognostic factor for ultimate facial nerve function is whether the facial paralysis is immediate or delayed. Often this is unknown, based upon the fact that health care providers are occupied managing the life threatening injuries in the first hours after any serious accident, and observations of facial nerve function are of secondary importance.
Measures to decrease swelling, such as administration of steroid medications, can sometimes hasten recovery. Another approach to relieve the squeezing phenomenon on the nerve is to perform a facial nerve decompression, though some feel this is a large operation for a problem likely to
Longitudinal Bone Fracture
resolve on its own. It is important to emphasize that in cases of delayed palsy, standard management is eye protection and patience. Regeneration falls along a spectrum, and ultimately facial nerve recovery can take over a year.
Transverse temporal bone fractures occur only 20% of the time, and usually result from a blow to the front or the back of the head. They tend to be more severe injuries, because the force required to fracture the temporal bone in its transverse dimension is greater than that required for longitudinal fracture. The pathway for these fractures may be directly through the inner ear hearing and balance organs, so hearing loss and vertigo are more common. The facial canal is also more commonly disrupted with a transverse fracture, with a 50% incidence of facial paralysis. Immediate onset facial paralysis with a transverse temporal bone fracture suggests disruption of the nerve, and should be repaired when the patient is medically stable. The complicating factor in head trauma is that commonly, other life threatening issues are occurring, and require substantial attention before the temporal bone fracture is addressed. Moreover, a good assessment of facial function requires a cooperative patient, and many patients are comatose following head trauma, making thorough examination of nerve function impossible.
Risk by Region
Lyme disease is a spirochetal infection caused by the organism Borrelia Burgdorferi. It is ordinarily transmitted through a deer tick vector, and is recognized by a characteristic “Bull’s Eye” lesion at the site of the tick bite. In the acute phase of the disease, this round red macule with a pale center is classic, though in up to 50% of infected individuals the lesion goes unrecognized or does not develop at all. The second phase of the disease, 3-6 weeks after infection, is characterized by migrating joint pains, fatigue, generalized weakness, and cranial neuropathies. It is during this phase that facial palsy may occur. This can affect one or both sides of the face. It can be isolated, or occur in conjunction with dysfunction of other cranial nerves. A blood test for the detection of Lyme disease is available, and confirmation of the disease requires antibiotic therapy.
Multiple Sclerosis (MS) is a demyelinating disease in which the sheaths surrounding myelinated motor nerves are broken down, preventing them from conducting signals appropriately. It can affect any motor nerve, including the facial nerve. It tends to wax and wane substantially, so that nerve function fluctuates according to the activity of the disease. During periods of disease remission, neural function often returns to normal.
Diabetes Mellitus (DM) is a lack of internal control over blood sugar levels, based on failure of the islet cells in the pancreas to produce insulin. Blood sugar levels are critical for maintaining proper homeostasis (balance of internal milieu), and lack of proper control over these levels causes many organ systems to develop disease prematurely. Amongst these systems is the nervous system; neuropathies are common in later stages of DM. The facial nerve, like any other nerve, is susceptible to malfunction on the basis of this DM-associated neuropathy.
Melkersson-Rosenthal Syndrome is characterized by a triad of three symptoms, including relapsing facial paralysis, facial edema, and a fissured tongue. It appears to have a familial inheritance pattern, though the specific mode of inheritance has not been established. A critical factor in this syndrome is that with each episode of facial palsy, recovery can be less satisfactory. For this reason, some doctors feel that facial nerve decompression is indicated, as this has been shown to decrease the severity of the facial palsy in subsequent episodes. This approach is generally reserved for severe cases with impending long term facial dysfunction, rather than for routine cases.
Recovery phases from bouts of facial palsy caused by Melkersson-Rosenthal syndrome tend to follow a similar time course to recovery from Bell's palsy, though bouts can get more severe and harder to recover from over time.
Facial weakness before parotid surgery
When facial weakness develops in the setting of a parotid gland mass, it suggests that the mass is impeding the function of the nerve. Tumors which impede neural function tend to be malignant cancers, rather than benign growths. Benign tumors can slightly push upon, but do not invade nerves. One exception is a facial schwannoma, which is a benign tumor that grows directly from the nerve, and can affect facial movements even though it is not a cancerous lesion.
For complete malignant tumor removal with pre-operative facial nerve weakness, it is very common for a portion of the facial nerve to be intentionally cut (sacrificed) to remove all the malignant cells. When this is the case, the nerve is often reconstructed using a donor piece of nerve from elsewhere in the body (neck, arm, or leg).
Parotid Gland and Facial Nerve
Facial weakness after parotid surgery
When facial nerve function is abnormal following parotid surgery, it is important to distinguish the cause of the weakness. The most common scenario is that the nerve is stretched during tumor removal, and in those situations complete recovery is likely. The degree of nerve dysfunction dictates the time frame of recovery. Complete facial paralysis takes longer to recover from than mild facial weakness, though when the nerve is anatomically intact, full recovery is the expected outcome.
In cases where the facial nerve must be cut in order to remove the entire mass with adequate margins, patients experience either partial or complete facial paralysis. Sometimes it is possible to perform a nerve graft at the time of surgery, in order to promote regeneration from the native facial nerve stump. In situations where the tumor extends deeply along the nerve or extensively into the facial musculature, grafting is not feasible, and other methods of facial paralysis management are employed.
Occasionally, patients develop acute onset facial paralysis accompanied by a vesicular outbreak, similar to chicken pox. Termed Ramsay Hunt syndrome (RHS), it is caused by the same virus that causes chicken pox (varicella virus). It tends to affect the balance and hearing organs as well, giving dizziness and/or hearing loss along with facial weakness. It is treated similarly to Bell’s palsy, but differs slightly because the varicella virus can actually cause nerve cell death, leading to slower and sometimes less complete recovery compared with Bell’s.
Facial Paralysis Related to Acoustic Neuroma and Other Skull Base Surgery
Occasionally, removal of an acoustic neuroma (vestibular schwannoma) or other skull base tumor in a similar location, results in postoperative facial weakness. This is related to manipulation of the facial nerve during tumor removal. Nerves are exquisitely sensitive to manipulation, and can be either temporarily or permanently damaged by surgical dissection around them. Tumors are often intimately associated with the facial nerve, and adherent to it. Removal of larger tumors has a higher probability of causing facial nerve dysfunction than removal of smaller tumors.
When the tumor is removed and the facial nerve is intact, but somewhat stretched during tumor removal, one can expect near complete to complete recovery over weeks to months. When the nerve is intact, but severely stretched or manipulated, partial recovery usually ensues over months to a year. Severely manipulated nerves that are not repairable occasionally do not yield any satisfactory recovery after 12-18 months. In these cases, facial reanimation options must be considered. Finally, sometimes the facial nerve must be divided for tumor removal. When grafting is not possible based on the anatomy, early facial reanimation procedures are appropriate.
There are many other infrequent causes of facial paralysis. Guillain Barre syndrome, an ascending polyneuropathy thought to be virally mediated, can give unilateral or bilateral paralysis. Many brain tumors, including pilocytic astrocytomas, "gliomas," ependymomas, and cavernous hemangiomas, or brainstem problems can lead to temporary or permanent paralysis, either from the disease or the therapy required to treat the disease. Cerebrovascular accidents (stroke) can lead to partial facial paralysis. Systemic illnesses such as diabetes, tuberculosis, and HIV can give facial paralysis, and certain other kinds of autoimmune diseases can also give facial weakness. Amongst the more common autoimmune diseases are Wegener’s granulomatosis, anti-phospholipid antibody syndrome, and lupus. Granulomatous diseases such as sarcoidosis have also been associated with facial paralysis, as in Heerfordt’s syndrome, also termed uveoparotid fever. For this reason, a thorough investigation for these rare causes must be undertaken, as each has a different treatment algorithm.