What could be more central to our sense of self than our faces? So imagine what it would be like to watch powerlessly while half your face progressively droops like melted wax. That's what happens in Bell's palsy.Bell's palsy is a condition causing weakness or even total paralysis of muscles on one side of face, typically developing over 3-72 hours. It can occur at any age and affects genders about equally. People with diabetes and depressed immune systems are at increased risk of having this condition, as are women in third trimester of pregnancy. Bell's palsy affects about 11 out of 1000 people sometime during their lives.
The problem lies within facial nerve, also known as seventh cranial nerve. The nerve is like a telephone-cable and contains thousands of individual nerve-fibers. There are two facial nerves, one for each side of face, and by far most common pattern is that one side of face is affected and not other.
The facial nerve ultimately connects brainstem (junction between upper brain and spinal cord located at base of skull) to muscles of face. Along way it travels through a narrow canal in skull bone. After exiting this canal near bottom of ear it divides into thousands of tiny branches before reaching facial muscles.
In Bell's palsy portion of nerve within skull's bony canal becomes inflamed for unclear reasons, though an infection with herpes simplex virus (the same virus that causes cold sores) is suspected in most cases. The condition is not contagious.
Because bony canal is rigid and narrow, swollen nerve-bundle has little room to expand, and compression of nerve-fibers can further injure them and cause more loss of muscle function. MRI scans of head can detect inflammation, but only if gadolinium (the MRI-equivalent of x-ray dye) is infused into a vein prior to scanning.
The weakness in lower facial muscles produces a lop-sided smile. Patients sometimes mis-identify side of their face that is affected: they focus on side of face that is "drawn" rather than on side that lacks ability to draw. Weakness in lower face also interferes with talking, eating and drinking, and beverages can dribble from corner of mouth. Weakness of upper face causes flattening of forehead-wrinkles and inability to raise an eyebrow.
But most significant problem is weakness in muscles that close eye, including those involved in blinking. Blinking—like other things we take for granted until they're gone—is an underappreciated but important activity that cleanses and moistens front of eyeball. So people with Bell's palsy experience dryness and irritation of eye on side of weakness. As a result, they try to blink even more frequently, but end up blinking unaffected eye more than eye that really needs it.
Other symptoms include pain in or behind an ear in about half cases. Pain usually fades within first 1-2 weeks of illness. Because branches of facial nerve modify senses of hearing and taste, patients can also notice excessive loudness of sounds, and foods might not taste as they should.