Thursday, March 17, 2011

Bell's Palsy 101: An Introduction to the Seventh Cranial Nerve

There are 12 cranial nerves. They are so named because they come off of the brainstem before the brain & brainstem leave the skull to become the spinal cord. They control things such as sight and movement of your eyes, smell, feeling and movement of your face, etc. Number 7, the Seventh Cranial Nerve, is primarily responsible for the movement of your face. Your brain thinks about moving your face and then the seventh cranial nerve relays that message to the muscles. It does some other things as well as you'll see below, but movement of your face is the major function (and most noticeable to other people when it's not working).

Okay, there are facts about Bell's Palsy below, but I think we should start with a basic anatomy lesson first. In this first image, I can appreciate that it looks complicated, but the basics are straight forward if you just read this through. On the left (the purple spot) is the nucleus, the start, of the seventh cranial nerve, the nerve which is the source of all your trouble. I circled and numbered some of the nerve branches that lead to your symptoms:
1. This leads to the tiniest bone in the human body in the ear, which helps soften sound so they will be comfortable. When not working properly sounds are louder in the affected ear.
2. When not working properly/inflamed, it causes pain behind the affected ear
3. Involvement of this is what contributes to dryness of the eye/eye discomfort and leads to the biggest complication of Bell's palsy, corneal abrasion, and potential vision loss if lubricating eye drops and a patch are not used.
4.This is what causes an unusual taste (or lack thereof). This nerve helps supply taste to the front part of your tongue.
5. This helps with keeping your mouth moist.
6. Last but definitely not least, this is where the actual weakness come from. All these branches weave into the upper and lower face to provide strength. Some people report "sensation change" but they are actually experiencing an unusual sense of "fullness" in the mouth because of the weakness rather than true sensation change. Other people have true "tingling" as the length of the nerve is affected by the inflammation. Other people truly do have additional sensation change because an entirely different nerve (the Fifth Cranial Nerve) can sometimes be affects as a kind of collateral damage.

I went through all that so you could see that depending on which of these symptoms you have, you can see potentially what part of the nerve is affected in your personally.

The second picture below in color shows the same nerve with some of the branches taken away for simplification, overlying a face to help orient us. Please note that the picture is also reversed, with the start of the nerve on the right in the second picture. Also, they put in some nearby nerves: Six, Five, and Eight so you can see that they're close by.

What are the first two things I think of when I see someone with weakness one side of the face in the ER or in my office?
1. Stroke
2. Bell's Palsy

**** I care about whether you can lift your eyebrow****
Patients always look at me funny when I focus on this during my exam, but it's important. Lifting your eyebrow is controlled by both sides of the brain. So you have a stroke on one side of your brain that makes your face weak, the other side of your brain will take over to help lift your eyebrow at least. BUT if the seventh cranial nerve is damaged after it leaves the brain, neither side of your brain can get to the eyebrow to lift it. Therefore a gross rule is this: Able to lift eyebrow=possible stroke. Can't lift eyebrow=possible Bell's palsy.

If it's a stroke, I have to decide where it is since that changes treatment options and workup quite a bit.
If it's a pure Bell's palsy, I have to decide how bad it is, what treatment to do depending on timing, and prognosis for recovery. Growing evidence implicated Herpes simplex virus type 1 as the most likely culprit in this.

I say pure Bell's palsy because a palsy of the seventh cranial nerve can potentially (depending on the patient and history) be caused by quite a few things: A run-amok ear infection, trauma, Lyme disease, Ramsey Hunt Syndrome, neoplasm/tumor.
And if you have bilateral seventh nerve palsy or a return of your facial weakness in the future to the opposite side, or other nerves affects such as those nearby ones in the picture above, I have to also consider all the above but also such things as: bad luck and you just got a pure Bell's palsy on the opposite side, Guillain-Barre syndrome/Miller Fisher syndrome, multiple cranial neuropathies for other reasons, pseudotumor cerebri, brainstem encephalitis, meningeal carcinomatosis, syphilis, AIDS, TB meningitis, pontine hemorrhage, lupus, Sjogren's syndrome, amyloidosis, diabetes, eclampsia if your pregnant, flu vaccine, neurosarcoidosis....

Bell's palsy is almost always straight forward, but you can see it can be quite exotic too, which is why you shouldn't just ignore it.

25 out of 100,000 people get Bell's palsy...but accounts for about 75% of all cases of one-sided facial weakness. So if you do get this weakness, probability is in your favor for it being this relatively benign process.
Most people have complete resolution within 3 to 6 months, although some people can have a subtle residual evidence on their driver's license photo when checked.
About 10% have recurrence.
Incidence is highest in those over age 70, and you have about the same chance of getting from age 30 through age 69. It's less common below the age of 29.
Most patients recover completely.
You have less of a chance of recovering completely if you are older, have hypertension, have impairment of taste, have pain other than behind the ear, and have complete facial weakness, have symptoms that progress more rapidly to fuller weakness over say less than 5 days than those that gradually get worse over more than 5 days.
The two most common symptoms (after slight residual weakness of course) include loss of vision if the production of tears is affected and the patient doesn't lubricate the eye appropriately, and something called "crocodile tears." Because there is sometimes damage to some of the nerves that go to the salivation gland, they can regrow incorrectly and connect to nerves responsible for tear production. The result is that when you have a salivary stimulus (you're hungry and a big tasty meal is placed before you), you may make tears. This saying comes from the fact that crocodiles are considered heartless predators and therefore "cry" while eating their tasty prey.


1.The best treatment for most people is tincture of time.
2. Studies are mixed about prednisone (taken at a decreasing dose by-mouth over 5 to 7 days) and antivirals such as acyclovir or valcyclovir. Taken within the first 24 to 48 hours of the start of the symptoms, most of us feel this is more likely to provide benefit in helping to reduce the severity of symptoms and possibly shorten the duration... although this is debated. It is agreed upon that taken after the first 24 to 48 hours, these medications are less likely to help.
3. Lubricating eye drops and an eye patch. Protecting the eye until it can close fully (at night as well) is essential in literally keeping your eye. Scratching the eye by rubbing against your pillowcase, your sleeve, etc. can quickly lead to infection and losing that eye.
4. Over the counter pain medications if you have pain in the distribution of the nerve (Aspirin, ibuprofen, Tylenol)
5. Moist heat applied to the face multiple times a day or before bed may help with the pain.
6. Physical therapy self-massage of the face and facial exercises may be helpful, and physical therapy is essential if you have additional damage to the nearby Eighth cranial nerve which can affect balance and walking.
7. B vitamins (B12 & B6) and zinc may help: They promote nerve health/growth.

Less likely to be helpful: Nerve decompressive surgery, biofeedback, acupuncture

There is so much more that could be said about Bell's Palsy. I hope this is a good start for you.