Diagnosis
Usually, the diagnosis of facial nerve palsy can be made on the basis of the physical examination. Since facial nerve palsy is a condition in which the facial muscles no longer function, this can be verified relatively easily by means of simple tests. The person affected is asked to frown or show their teeth, for example.
In most cases, only one half of the face is affected by facial nerve palsy, so these simple tests can reveal paralysis of the nerve relatively quickly. If an infection is suspected, the blood and, if necessary, the cerebral fluid should also be examined by means of a lumbar puncture. Imaging, e.g. a CT, is usually not necessary in facial nerve palsy.
What is the difference between central and peripheral facial paresis?
In order to understand the difference between central and peripheral facial nerve palsy, it is necessary to take a closer look at the course of the cranial nerve. Every person has two facial nerves that originate in two small nuclei (a right and a left nucleus) in the brainstem. However, the command for the movement of the muscles comes from further up through other fibers.
These fibers in turn originate in the cerebrum. This is an area of the brain that is responsible for controlling all muscles. From there, the fibers travel down to the nuclei in the brain stem.
On the way there, a part of them crosses over to the other side. In this way, the right core in the brain stem receives information from the area of the right hemisphere as well as from the left hemisphere, and vice versa. If central facial nerve paresis now occurs, the fibers in the cerebrum are affected.
As a result, the nerve supply to the facial muscles on the opposite side of the damage fails because some of the fibers cross over to the other side on their way to the brain stem. This part is mainly responsible for the muscles of the mouth, nose and cheeks. This means that the affected person can no longer show his teeth or turn up his nose, for example.
However, the muscles around the eyes and forehead are still intact, as these fibers both cross and pull straight down from the side of the brain. These muscles are therefore controlled by fibers from both hemispheres of the brain and are therefore not affected by central facial nerve palsy. In peripheral facial nerve palsy, the nucleus in the brainstem or the nerve on its way to the muscles is damaged. As a result, all muscles on the side of the damage fail and the affected person can no longer frown or close his or her eye on this side.
