Bell's Palsy
From Medical-Wiki
Bell's Palsy, also known as idiopathic facial paralysis (IFP), is a unilateral peripheral paralysis of the face owing to neuritis of cranial nerve 7. It is most often manifested as an abrupt or acute functional impairment and paresis of the muscles of facial expression for a limited duration. Bell’s Palsy is the most common cause of unilateral facial weakness.
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Frequency
Bell's Palsy is diagnosed in approximately 25 of 100,000 people a year, affecting people of Japanese descent with slightly more incidence than the rest of the world. Patients are usually between the ages of 15-60 years old.
Pathophysiology
The pathophysiology of Bell's Palsy is not entirely clear, but is most likely related to compression of the facial nerve due to demyelination, inflammation, or ischemia (inadequate blood supply). The facial nerve is responsible for contraction of the muscles of the face in expression, lacrimation, and the senses of taste and hearing. As a result of its convoluted path through the temporal bone which is only slightly larger in diameter than itself, the 10,000 neurons that exist in the facial nerve are prone to impairment due to vascular congestion with secondary ischemia.
Clinical
Most people who present with Bell’s Palsy are usually very frightened and fear that the condition is irreversible or due to tumors or stroke. Taking an adequate history is vital in making a diagnosis of Bell’s Palsy to rule out emergent situations such as cranial trauma.
History of the patient may include the following-
•Facial weakness
•Inability to close eye or dry eyes
•Sagging of the mouth
•Loss of nasolabial fold
•Taste loss in anterior 2/3 of tongue
•Hyperacusis, which is impaired tolerance to typical sound levels
Physical examination of the patient-
This test should focus specifically on cranial nerve 7, however should also include a neurological examination of all cranial nerves. [1]
Testing for cranial nerve 7 includes:
•Eyebrow elevation
•Forehead wrinkling
•Frowning
•Tight closing of eyes
•Showing teeth
•Puffing cheeks
•Testing taste sensation of anterior 2/3
Risk Factors
•Bell’s Palsy can be a symptom of another disease process that is taking place in the body. As a result, the differentials are often grouped with risk factors for Bell’s Palsy. Bell’s palsy has been associated with viral etiologies that elicit an immunological reaction such as Herpes Simplex Virus type 1 (HSV-1) and Herpes Simplex Virus type 2 (HSV-2),Varicella Zoster Virus (VZV), Mycoplasma, Influenza B, Ebstein Barr virus (EBV), Cytomegalovirus(CMV)
•Bell’s Palsy is also associated with any condition that depresses the immune system
•Symptoms of Bell’s Palsy have also been shown to increase during pregnancy
•Genetics has been implicated in Bell’s Palsy
•HIV
•Stress
•Diabetes
Differentials
•Temporal bone abscess
•Trauma
•Iatrogenic surgical injury
•Intracranial lesions including tumors, AVMs, infarcts
•Nerve tumors
•Rhabdomyosarcomas
•Polio in endemic areas
•Hypertension
Workup
Diagnosis is typically based on history and findings on physical examination [discussed above]. However, a further workup is often helpful in pinpointing the etiology or ruling out other processes.[2]
•Imaging studies include an MRI to rule out the possibility of a stroke or brain tumor. MRI is usually done if there is a gradual loss of hearing or slow onset to paralysis
•Lumbar puncture is performed to rule out immunologic causes such as Multiple Sclerosis
•Lyme titers are done to rule out Lyme disease
•Audiometry, which is a test of hearing ability
•Electrodiagnostic testing, which measures the electrical activity of muscles and nerves
•Electroneurography, which is the measurement of nerve speed conductions
Treatment
Bell’s Palsy is typically self-limited and improves with time. Physicians promote a trial use of steroids, such as glucocorticoids, to reduce inflammation surrounding the facial nerve in the hopes that it will reduce compression.
Some experts also suggest the addition of anti-viral drugs that may be causing the swelling of the nerve.
References
[1] Bruce Lo, MD. Bell's Palsy. Emedicine. http://www.emedicine.com/emerg/TOPIC56.HTM
[2] Craig H Zalvan, MD. Bell's Palsy. Emedicine. http://www.emedicine.com/ent/TOPIC719.HTM
