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Etiology of Bell's Palsy

As sited by numerous journals and references, Bell's Palsy is a diagnosis resulting from the process of elimination of other Facial Palsy causes. Left and right side paralysis occurs equally. Its etiology remains unknown, although various studies have led people to believe that it is a mononeuritis cranialis or neuritis vestibularis induced by either a viral infection or an autoimmune disease(Schrader and Sumner, 1996).

Acquisition of these recent infections and diseases are all considered to be associated factors to possible episodes of facial paralysis (Billue, 1997):
- Upper Respiratory infections
- Ear infections
- Epstein-Barr virus
- Cytomegalovirus
- Group G Streptococcus
- Mycoplasma
- Kawasaki Disease
- Chlamydia
- HIV
- Herpes Simplex Virus
- Diabetes
- Hypothyroidism
- Hypertension
- Cancer
- Syphilis
- Sarcoidosis
- Multiple Sclerosis

THE VIRAL ETIOLOGICAL HYPOTHESIS:
This theory of Bell's palsy having a viral etiology was initially based on clinical symptoms such as fever, coryza and sore throat (which may also precede facial paralysis). At first glance, there is no strong epidemiological evidence for a viral etiology since most cases develop randomly with little evidence of epidemic clustering by time and location. Only microorganisms that can reactivate from a latent state may fit into such non-epidemic patterns. The herpes viruses are known to become latent after initial infection and hence are important candidates to consider in the etiology of Bell's palsy. The two highly neurotropic herpes viruses that researchers consider are HSV and VZV. After infection, these viruses travel along the sensory nerves to establish latency at the sensory ganglia. Both forms of herpes are known to reactivate; leading to herpes labialis or herpes genitalis in the case of HSV, and herpes-zoster in the case of VZV. Reactivation of VZV induces facial paralysis known as Ramsay-Hunt syndrome "herpes-zoster oticus". These patients are not considered to be true Bell's palsy patients, leaving the herpes simplex virus to be the only other etiological explanation of Bell's palsy when considering the viral hypothesis.


RISK FACTORS:
Contrary to popular belief, the incidence rate is not disproportionately high in pregnant women, but is higher amongst diabetics than in the normal position (Adams & Victor, 1993). There is no predilection to either sex. Climate is not a contributing factor either. Seventy percent of patients with Bell's Palsy relate a previous upper repiratory infection, and ten percent report a family incidence with the disorder. A higher prevalence has been sited among lower socioeconomic groups (Billue, 1997).

SIGNS & SYMPTOMS:
The onset of Bell's Palsy creates maximal unilateral motor deficits occurring over a few hours. Pain behind the ear is a common symptom that generally precedes paralysis by one or two days, as well as fever, tinnitus, and a slight hearing deficit. Voluntary and involuntary movements of the muscles are affected, and often impaired. Obvious physical signs that the patient exhibits are facial asymmetry, drooling, a widened palpebral fissure, smooth forehead, and a flattened nasolabial fold causing a depressed cheek. Symptoms not associated with Bell's Palsy are facial twitching, otorrhea, severe otalgia, and balance dysfunction.

The most significant symptoms supporting idiopathic facial paralysis are:
1. An acute or subacute facial weakness of the upper and lower muscles of the face.
2. Postauricular pain.
3. Lacrimation