A 39-year-old-male presented to the emergency department with a chief complaint of one day of left-sided facial swelling and weakness. He denied facial pain, rash, vision changes, fever or chills. He had recently returned from a trip to the mountains but denied any bites/stings. On physical exam he was noted to have mild swelling over the left parotid gland as well as a left-sided seventh nerve palsy without forehead sparing (inset). The nerve paralysis was complete including inability to purse lips (top left) or smile on the left side (top right). He had no other neurologic deficits.
Idiopathic facial nerve paralysis, commonly referred to as Bell’s palsy, was first described by Sir Charles Bell in the 1800s. His description was of facial trauma causing unilateral facial nerve paralysis. However, “Bell’s palsy” is now used to refer to any peripheral seventh nerve palsy without a known cause. The annual incidence is estimated at 20/1000003 with a lifetime risk of 1 in 652. While the cause is unknown, the herpes simplex virus (HSV) has previously been implicated due to the presence of HSV DNA in endoneurial fluid of 11 of 14 patients with Bell’s palsy and absence of HSV DNA in control patients1. Inflammation of the facial nerve, as it courses through the fallopian canal in the temporal bone, is generally accepted as the mechanism that leads to edema, ischemia and ultimately demyelination of the nerve6. While men and women are affected equally by Bell’s palsy, there is an increased risk in those with diabetes and women who are pregnant or recently post-partum.
Recognizing central versus peripheral seventh nerve palsy is the first step in diagnosis. Central facial nerve palsy causes paralysis of only the lower half of one side of the face. This is caused by damage to the upper motor neurons of the facial nerve. The facial motor nucleus contains two regions with lower motor neurons that supply the muscles of the face. The ventral region supplies the muscles of the lower face, while the dorsal region supplies the muscles of the forehead. The corticobulbar tracts from the dorsal region cross the brainstem several times while the ventral tracts cross only once; giving bilateral cortical input to the dorsal fibers but unilateral input to the ventral fibers. Thus unilateral lesions of the corticobulbar tracts will cause paralysis of the lower face while sparing the function of the forehead and eye musculature.
In contrast, peripheral seventh nerve palsy occurs when the facial nerve fibers are damaged after exiting the brainstem thus both tracts are affected resulting in paralysis of both upper and lower face muscles. This causes progressive onset of the characteristic unilateral facial paralysis involving the forehead, eye and lower face. This paralysis may be partial or complete so it is important to compare both sides of the face to determine if the upper face is involved. The most sensitive way to do this is have the patient close the eyes and attempt to keep them closed while the examiner tries to open them. This can detect subtle weakness of the orbicularis occuli that would be seen only in peripheral seventh nerve palsy. Hyperacusis, decreased tear production, and loss of taste on the anterior 2/3 of the tongue as well as posterior auricular discomfort can also be seen in Bell’s palsy.
It is important to note that Bell’s palsy is a diagnosis of exclusion and it is necessary to first rule out potential known causes of peripheral facial nerve paralysis. These causes can generally be divided into three categories; infection, trauma and neoplasm. History of possible exposure to Lyme disease is important to ascertain, especially in patients with bilateral facial nerve paresis, as early initiation of antibiotics is necessary to preserve nerve function. Physical exam with evidence of vesicles or rash suggestive of Herpes Zoster or evidence of otitis media or externa can also help guide treatment. A history of trauma to the temporal bone preceding the facial nerve dysfunction suggests nerve transection or compression secondary to fracture and warrants evaluation by an otolaryngologist. A final known cause of facial nerve paresis is neoplasm, particularly a parotid gland tumor. A history of gradual onset of weakness, involvement of multiple cranial nerves, recurrent dysfunction or prolonged symptoms is suggestive of neoplastic disease and warrants imaging.
Treatment of Bell’s palsy varies and is usually directed toward a presumed cause (HSV) or to decreasing the inflammation causing the nerve dysfunction. Treatment controversy generally centers on the efficacy of steroids +/- antiviral medication. While the efficacy of treatment with steroids has been questioned, more recent studies demonstrate clinically significant recovery of nerve function over patients treated with placebo alone4,5. Recent meta-analyses have also evaluated the addition of either acyclovir or valacyclovir to prednisolone in the treatment of Bell’s palsy. Despite inclusion of larger clinical studies, they still failed to show clinically significant improvement in neurologic recovery with the addition of antiviral agents. The authors found a 40% greater likelihood of recovery at three months with the addition of anti-virals over prednisolone alone but this did not reach statistical significance3. Sub-group analyses suggest a trend toward improvement in very severe Bell’s palsy when anti-viral treatment is added but there is currently insufficient evidence to recommend routine use. Current best evidence recommends treatment with corticosteroids within 48 hours of symptom onset.
1. Murakami S, et al; Bell’s palsy and herpes simplex virus: Identification of viral DNA in endoneurial fluid and muscle. Ann Intern Med 1996; 124:27.
2. Browning G; Bell’s Palsy: a review of three systematic reviews of steroid and anti-viral therapy. Clin Oto 2010; 35, 56-58.
3. Numthavaj P, et al; Corticosteroid and antiviral therapy for Bell’s palsy: A network meta-analysis. BMC Neurol; 2011, 11:1.
4. Sheikh S, Jacobus C; Are steroids effective for treating Bell’s palsy? Ann Emerg Med. 2012 Jan;59(1):33-4.
5. Berg T, et al; The Effect of Prednisolone on Sequelae in Bell’s Palsy. Arch Otolaryngol Head Neck Surg. 2012;138(5):445-449.
6. Jackson C, von Doersten P. The facial nerve. Current trends in diagnosis, treatment, and rehabilitation. Med Clin North Am. 1999;83:179–195.
Dr. Kristy Rahimi is a 3rd year Emergency Medicine Residents at the Denver Health Emergency Medicine Residency Program. Dr. Bonnie Kaplan is a Senior Instructor at UCHSC. Dr. Peter Pryor is a faculty member at Denver Health, an Assistant Professor of Emergency Medicine at the University of Colorado School of Medicine and has an academic focus in medical photography.