Both major and minor long-term complications can ensue from Bell’s palsy in 30% of the patients, and 5% of them are left with a high degree of sequelae. In case of incomplete or aberrant regeneration of damaged nerve fibers, a phenomenon known as synkinesis can occur.
During regrowth, some nerve fibers originating from facial nerve can sidetrack and erroneously connect with the lacrimal ducts instead of the salivary glands. In such instances patients will shed tears while eating, which is in medical literature also known as crocodile tear syndrome, Bogorad's syndrome or gustatolacrimal reflex.
Other example of synkinesis is when the nerves controlling the eye muscles misdirect and regrow connections with the muscles of the mouth. Abnormal movement or different facial muscle group occurs afterwards, since movement of one muscle can now affect the other one. For example, the corner of the mouth can involuntarily lift when the affected individual closes the eye. Such synkinesis is often treated with botulinum toxin injections (Botox) and facial reanimation by means of cosmetic surgery. Botulinum injections are sometimes administered to the non-affected side as well, in order to improve facial symmetry.
Incomplete motor regeneration is also an important long-term complication. As the largest portion of the facial nerve contains efferent fibers for stimulation of facial muscles and formation of facial expressions, subpar regeneration in this part of the nerve can result in permanent paralysis of all or several muscles on that side of the face. That can in turn manifest as an inadequate function of the mouth, excessive tearing (epiphora) and nasal obstruction.
Incomplete sensory regeneration can also occur as a result of Bell's palsy. Deterioration or loss of taste (also known as dysgeusia or ageusia, respectively) can occur after partial regeneration of the chorda tympani (an important branch of the facial nerve that carries taste information from the anterior part of the tongue). If other afferent branches are affected, a change or sensation to normal stimuli can occur. This condition is known as dysesthesia, although it is still a controversial topic as it seems other cranial (glossopharyngeal or trigeminal) nerves are also involved.
Recent studies show that Bell’s palsy can increase the risk of non-hemorrhagic stroke. That particular finding can be linked to previous research that has shown an increased risk of stroke in patients with HSV-1. The pathogen in question has also been implicated in inflammation, vasculopathy and atherosclerosis in the cerebral blood vessels. All things considered, a multi-specialist approach is needed when dealing with a myriad of complications arising as a result of Bell's palsy.