Commentary by Aaron Lord MD, PGY-1
A 39 year-old woman awakes one morning and notices that the left side of her face is droopy. While at work, she has trouble controlling her saliva and it dribbles down the left side of her chin. At dinner, she has trouble eating and notices food stuck between her lips and teeth on the left side. The next morning she sees her primary care physician with the above complaints and also says she has noticed excessive tearing from the left eye. Neurological exam shows the following left-sided deficits: loss of the nasolabial fold, unfurrowing of the brow, inability to close eyelids (with upward deviation of the eyeball when attempting to close the eye), decreased lacrimation, corneal abrasion, and loss of taste on the anterior left 2/3rd of the tongue.
The etiology of Bell’s Palsy has remained elusive since it was first described over a hundred and fifty years ago by the Scottish surgeon Charles Bell (who interestingly wrote one of the first treatises on the anatomy of facial expressions for painters). More recent research in the mid- to late-1990’s led some observers to believe that HSV-1 may play a role, and acyclovir was added to the standard treatment protocol by many providers. New research, however, has called that practice into question, making the etiology of the disease as enigmatic and elusive as ever.
Bell’s Palsy is a peripheral-nerve palsy, usually unilateral, affecting the facial nerve (CN VII) at the level of the geniculate ganglion. It affects 15-30 out of 100,000 individuals every year and people with diabetes, pregnancy, or in their 40s tend to be more affected.
Observations by surgeons and neuroradiologists show that there is inflammation and edema of the affected facial nerve at the level of the geniculate ganglion. At this location, the facial nerve carries not only the motor fibers that innervate the muscles of facial expression and stapedius muscle in the middle ear, but also autonomic fibers that control lacrimation, salivation, and taste to the anterior 2/3 of the tongue. Patients usually present with the acute onset (hours to 1-2 days) of unilateral facial weakness which may progress to complete paralysis by the third or fourth day. There is loss of facial folds and furrows, drooping of the mouth with dribbling of saliva, inability to clear food from between the teeth and lips on the affected side, and inability to close the eyelid completely. The upward rotation of the eye when attempting to close the eyelids is known as Bell’s Phenomenon. Tear production is actually decreased due to loss of parasympathetic fibers to the lacrimal glands, but the drooping of the lower lid and spillage of tears leads to complaints of excessive tearing. The cornea often drys out and can suffer from abrasions due to exposure and dryness.
The differential diagnosis for a patient who presents with unilateral facial weakness includes both peripheral and central causes. Other peripheral causes include Lyme Disease, otitis media, Ramsay Hunt Syndrome (zoster of the 7th cranial nerve), Guillain-Barre Syndrome, and compression by a tumor of the parotid gland. Thus it is important to ask for recent tick exposure, rashes, arthralgias, ear pain or fever, appearance of vesicles in the external auditory canal, and weakness in other parts of the body. Central causes include stroke, tumor, and multiple sclerosis. Central causes will usually be associated with other neurological deficits or weakness of other body parts, mental status changes, and sparing of weakness in the forehead muscles due to bilateral innervation, so a good history and physical exam are necessary. Obtaining imaging is usually not necessary without any of these other central symptoms.
The idea that HSV-1 (and other herepes family viruses) may play a part in the etiology of Bell’s Palsy was fostered in the 1980s with a study that showed a higher prevalence of herpes simplex virus (HSV) antibodies in Bell’s Palsy patients when compared to controls. With the newly invented technique of PCR, researchers in the 90′s reported case-studies showing the detection of HSV-1 DNA in the geniculate ganglions of individual patients with Bell’s Palsy, helping to firm up HSV-1′s role. Other research has arisen, however, refuting HSV-1 significance in the etiology of Bell’s Palsy. A Swedish group recently published a series of 20 face muscle biopsies and detected HSV and VZV DNA in 1 patient each (5% of samples per virus) and no increase in serum antibody titers to HSV. Moreover, a Japanese group recently showed reactivation of HSV-1, VZV, or both viruses in only 15.3%, 14.7%, and 4.0% of patients, respectively. The most recent evidence refuting the etiological role of HSV-1 was a case-control study published this summer by Kanerva et. and showed no evidence of HSV-1 DNA (as detected by PCR) in any of the patients suffering from Bell’s Palsy (or the controls for that matter).
The standard treatment for Bell’s Palsy is glucocorticoids (10-14 day taper), with many providers adding acyclovir to their regimens. A recent randomized, double-blinded, placebo-controlled trial published by Sullivan et al. (like Bell, the group is also from Scotland, more specifically, Dundee) in the New England Journal of Medicine showed that use of prednisolone within 3 days of onset resulted in recovery rates of 94.4% for those treated versus 81.6% for those who received placebo. The study additionally looked at whether acyclovir was effective in improving recovery rates. They found that those who received acyclovir (alone or with prednisolone) actually had worse recovery rates than those who received placebo. A less well-designed trial did show some benefit to acyclovir in those with complete paralysis, but for the vast majority of patients, the use of antivirals appears to be unnecessary and calls the role of HSV-1 into question. These results, along with the PCR and immunological studies noted above, seem to suggest that even if HSV or other herpes viruses play a role, it may not be as significant as once thought.
Patients should also use eye drops in their affected eyes, and often benefit from an eye patch, especially while sleeping. Those patients who do not experience full recovery often experience muscle contractures and may need surgery to help with eye lid closure. For those who do fully recovery, there are often sequellae from abnormal nerve regeneration: synkinesis—where movement of the mouth may result in narrowing of the palpebral fissure, or blinking may result in mouth twitching—as well as “crocodile tears”—inappropriate lacrimation while eating due to crossed innervation of salivation and lacrimation pathways.
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