A family history of Bell’s palsy has been reported in approximately 4% of cases.(1) Bell’s palsy is the most common cause of one-sided facial nerve paralysis.(1)
How Can You Tell The Difference Between A Stroke & Bell’s Palsy?
Bell’s palsy and stroke are two important causes of paralysis of facial muscles. The characteristic of both these conditions is that they can present as an acute condition within the phase of 48 hours. So, it becomes very important for emergency care providers to differentiate between these two conditions because one of these conditions is time-dependent and requires medical attention as soon as possible. Stroke has to be treated within 3 to 6 hours because it can improve if the treatment is done at the earliest. Whereas the case is not the same for bell’s palsy because it may take days to years for the cure of bell’s palsy. Sometimes Bell’s palsy also does not get cured completely depending upon the etiology.
To be able to differentiate between these two conditions, it is very important to first understand both of them and their mechanism. In Bell’s palsy, there is the involvement of facial nerve which can be unilateral or bilateral. The facial nerve is a seventh cranial nerve which supplies muscles of the face ipsilaterally that is on the same side because these are two in number. It is a lower motor neuron which originates from the pons (a part of the brain stem) and descends/run forward to supply muscles of the upper face as well as the lower face.
Now the facial nerve carries innervation from the nucleus of the 7th nerve which comprises sensory and motor fibers descending from the motor and sensory areas of the cerebral cortex. These are arranged differently as compared to fibers of the facial nerve. The lower motor fibers which originate from the upper part of the cerebral cortex descend till the brainstem and cross over to the other side to supply the lower area of the face only. While in the case of upper motor fibers of the face which originates from the lower part of the cerebral cortex descends till the brainstem and half of the fiber crosses over on the other side while the other half remains on the same side. This way the upper motor fibers of the face supply both sides of facial muscles.
Now when a stroke which is usually a cerebral ischemic stroke of the motor area of the cerebral cortex occurs, it can involve either upper or lower motor fibers depending upon the site of the blockage. If the upper motor fibers are involved then there is no facial paralysis because the upper area of the face has dual innervation but if the lower motor fibers are involved then there is facial paralysis of the lower quadrant on the contralateral side to that of blockage. The characteristic is that only the lower half of the face is involved while the upper half of the face is normal. It presents with a deviation of mouth on the normal side, inability to fill the air in the cheeks, deviation of the upper lip while smiling, etc.(2)
While in the case of Bell’s palsy, there is a complete loss of function of facial muscles on the same side as that of involvement of facial nerve. It can present with the features of drooping of the eyelid, loss of forehead creases, loss of nasolabial folds in addition to all the symptoms of the facial paralysis of the lower quadrant.
It is very much important for an emergency care service provider to differentiate between stroke and facial/Bell’s palsy because the treatment plan varies widely and is also time-dependent.