Viral and bacterial infections, as well as autoimmune disorders, appear to be emerging as the most frequent common thread in the etiology of Bells palsy.
HERPES SIMPLEX 1
As far back as 1970, Herpes Simplex 1 was suggested as a cause of Bell's palsy (Dr. Kedar Adour). Some Bells palsy must still be designated as idiopathic, but a 1995 study (Dr. Shingo Murakami and others) points compellingly to the herpes simplex virus (HSV-1) as the most frequent cause of Bell's palsy, possibly accounting for at least 60 - 70% of cases. Additional research since this study was published has been reinforcing the conclusion.
Exposure to HSV-1 is common; a vast majority of the population has been exposed to it. Most people are exposed during childhood. Kissing between relatives is the most frequent source of exposure, but it may be possible that the virus is also spread while sharing towels, utensils, etc. The active virus is commonly associated with cold sores, but the virus often runs its course without causing any blisters - blisters actually appear only 15% of the time. This results in a large population of HSV-1 carriers who do not know they've been exposed to the virus. HSV-1 is infectious for a short time following the incubation period. It then enters a dormant state, residing on nerve tissue. There are several triggers that can cause the dormant virus to reactivate. As this site is about Bell's Palsy, rather than herpes, we will not address issues concerning herpes outbreaks where the reactivated virus sheds to the skin. When the latent virus reactivates at the facial nerve the immune system begins to produce antibodies, causing an inflammation. This is a normal function, and is part of the process that eliminates harmful foreign bodies such as viruses and bacteria so that we can recover from illness and injury. If the location of the inflammation is within the fallopian canal (described above) there is no room for the swelling to expand. The nerve itself becomes inflamed, or the inflammation within the canal exerts pressure on the nerve. The result is that the nerve is compressed inside its bony tube. Compression of the nerve is the injury that stops transmission of signals to muscles. Unable to receive signals to contract and relax, the muscles become temporarily weakened or paralyzed.
The triggers for reactivation of the virus prior to the onset of Bell's palsy have not been proven conclusively. Impaired immunity, whether temporary (stress, lack of sleep, minor illness, physical trauma, upper respiratory infection, etc.) or long-term (autoimmune syndromes, chronic disease, etc.) are strongly targeted as the most likely triggers.
OTHER VIRAL LINKS
There has been research implicating other viruses, including cytomegalovirus, Epstein-Barr, rubella and mumps, in the etiology of Bell's palsy. As with the herpes virus, potential triggers appear to be related to conditions that affect the immune system. The internal process that would cause the nerve to become compressed and result in Bells palsy is currently thought to be the same as described above for the Herpes virus.
RAMSEY HUNT SYNDROME
Ramsey Hunt syndrome is similar to Bell's palsy. Unlike Bells palsy, the virus that causes Ramsey-Hunt syndrome has been conclusively identified. It is varicella zoster virus (VZV), which is the virus that causes chicken pox, and is a strain of the Herpes virus. Like HSV-1, it remains in the body, residing on nerve tissue in a dormant state on nerve ganglia after the initial infectious stage has passed. VZV typically remains dormant for decades. The incidence of Ramsey Hunt syndrome increases significantly after age 50. Younger patients with Ramsey-Hunt syndrome are often advised to be tested for autoimmune deficiencies.
Ramsey-Hunt syndrome results in symptoms that are in many respects identical to Bell's palsy. The symptoms are so alike that a diagnosis of Ramsey Hunt syndrome can easily be missed.
When the VSV virus is reactivated the resulting eruptions (blisters) are known as shingles. The first symptom is usually severe pain. There may also be a fever, headache, and localized tenderness. Blisters typically begin to emerge 1.5 to 3 days after the onset of these symptoms, although they may emerge with no prior symptoms.
Symptoms of Ramsey Hunt Syndrome
In addition to the "classic" symptoms of Bells palsy, Ramsey Hunt syndrome is associated with some additional symptoms that help differentiate it. Knowledge of these symptoms is key to an early diagnosis, and should be brought to a doctor's attention during the first visit, or when any of these symptoms become apparent.
1. Pain: Bell's palsy patients may complain of pain (often in or behind the ear) which can be acute. However, it will tend to fade within a week or two. The pain associated with Ramsey Hunt syndrome is often more severe, and more likely to be felt inside the ear. It may start before muscle weakness is apparent, and may last for weeks or months - sometimes longer. Medications such as Neurontin can ease the post-herpatic pain of Ramsey Hunt syndrome.
2. Vertigo: Dizziness is occasionally reported by Bells palsy patients, but is often associated with Ramsey Hunt syndrome. It can be more severe, and longer lasting.
3. Hearing loss: Unlike Bell's palsy, Ramsey Hunt syndrome can also affect the auditory nerve (CN-VIII), resulting in hearing deficit. This should not occur with Bells palsy, and is an important clue to the diagnosing physician. In some cases hearing loss will continue after facial muscle function returns.
4. Blisters: The primary symptom that makes a diagnosis of Ramsey Hunt syndrome likely is the appearance of blisters (known as shingles, or herpes zoster) in the ear. The blisters can appear prior to, concurrent to, or after the onset of facial paralysis. They can be expected to last 2 - 5 weeks, and can be quite painful. The pain can continue after the blisters have disappeared. Blisters are often the only clearly visible symptom that identifies Ramsay Hunt. Unfortunately, they may not be evident during the diagnostic examination. They can be present, but too deep within the ear to be visible. Or they can be too small to be seen. In some cases they may not appear until a week or more after the onset of muscle weakness. At times they do not appear in the ear at all, but may be present in the mouth or throat. It is also possible for the virus to reactivate without blisters at all.
5. Swollen and tender lymph nodes near the affected area.
While Bell's palsy is not contagious, shingles blisters are infectious. Contact with an open blister by someone who has never had chickenpox can result in transmission of the virus. The result will be chickenpox, not shingles or facial paralysis.
** If you've been diagnosed with Bell's palsy, but later see blisters that may be shingles, its important that you notify your health care professional. **
HIV / AIDS
HIV can cause facial paralysis and increases the chance of developing Ramsey Hunt syndrome, as well as Bell's palsy. In the early stage of HIV, paralysis can be directly due to the viral infection. In later stages paralysis is more likely to be associated with the opportunistic infections or tumors associated with severe immune deficiency. Herpes zoster has been confirmed to be associated with suppressed immune systems.
Lyme disease can cause facial paralysis and the same symptoms as Bells palsy. Bacteria enter the body through the skin at the site of the tick bite. Typical early symptoms of Lyme disease are a red ring around the site of the bite and flu-like symptoms. Unfortunately these symptoms do not always appear. The early symptoms will pass, but administration of an antibiotic as early as possible is important to avoid serious problems later. Without an antibiotic the bacteria can spread throughout the body, causing arthritis, heart disease, and nervous system disorders such as facial paralysis.
Otitis Media - Bacteria from some acute or chronic middle ear infections can invade the canal around the nerve through small portals. As with viruses, the presence of bacteria can evoke an inflammatory response, and compress the nerve.
Bell's palsy and Ramsey Hunt syndrome can be bilateral, but it's extremely rare. Mononucleosis, the flu, Guillain - Barre Syndrome, leukemia, lyme disease, sarcoidosis and Heerdfort's Syndrome are among the potential triggers of bilateral palsy.
Melkersson-Rosenthal syndrome can result in unilateral or bilateral palsy. The palsy will tend to be recurrent, to such an extent that it's sometimes described as intermittant or bilateral. Recurrences don't follow any pattern - each recurrence can be on the same side, alternating side, or bilateral.
Diagnosis of this syndrome can easily be missed, as the obvious symptoms may look like Bells palsy. However, unlike Melkersson-Rosenthal syndrome Bell's palsy recurrences tend to be separated by wide timespans.
OTHER CAUSES ...
Facial and surgical wounds, trauma due to a blunt force, temporal bone fractures, brain stem injuries, acoustic neuromas, cysts and tumors can result in facial palsy. Diabetes and thyroid conditions are also associated with facial palsy. Lupus, Sjogrens syndrome and congenital defects can, infrequently, cause facial paralysis.