The Neuropathies
Ethan Abbott
Although the neuropathies represent a broad, complex, and heterogeneous group of disorders, this chapter presents several distinct and commonly evaluated neurologic emergencies encountered by the acute care provider: Bell’s palsy, Guillain-Barré syndrome (GBS), and the peripheral neuropathies with a focus on distal symmetric polyneuropathy (DSPN). With evolving evidence and questions regarding the efficacy of medications and timing of acute interventions for several of these conditions, this chapter helps guide the clinician with a focused approach based on the best available evidence.
BELL’S PALSY
THE CLINICAL CHALLENGE
Bell’s palsy is an idiopathic, cranial nerve VII (facial) paralysis and the most common cause of unilateral facial nerve weakness or paralysis. The etiology is thought to be viral-mediated, but the pathophysiology is controversial. Management focuses on protecting the eye from injury and minimizing long-term sequelae.
Bell’s palsy typically presents as an acute-onset, unilateral facial palsy peaking at 48 to 72 hours after the start of symptoms; the average age for presentation is 40. The clinical challenge with a facial palsy is to determine whether it is central or peripheral in origin. There are potential pitfalls that can occur, leading to missed or delayed diagnosis that may contribute to increased morbidity. It is estimated that up to 30% of patients will have a delayed or incomplete recovery of full function, resulting in permanent disability.1 Bell’s palsy is commonly seen in patients with diabetes, hypertension, a recent upper respiratory infection, or in late-term pregnancy. Table 8.1 presents the differential diagnosis for unilateral facial nerve palsy.
PATHOPHYSIOLOGY
Understanding of the facial nerve anatomy and innervation is essential to differentiating central from peripheral causes of facial nerve palsy. The facial nerve innervates the muscles of facial expression, including the orbicularis oculi, frontalis, orbicularis oris, and the stapedius. It supplies sensation to the anterior two-thirds of the tongue, and the parasympathetic fibers of the lacrimal and submandibular glands. Because the cells of the facial nucleus that innervate the upper face receive fibers from bilateral hemispheres, a patient with the ability to move the forehead muscles should raise concern for a central etiology. Thus, in a patient with a peripheral facial nerve palsy such as Bell’s, complete weakness of the ipsilateral facial nerve involves the entire forehead. Bilateral symptoms are uncommon, and should trigger considerations for an alternative diagnosis such as Lyme disease.
TABLE 8.1 Etiologies and Clinical Features of Facial Paralysis | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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The facial nerve travels through the narrow fallopian canal within the temporal bone. Its anatomic course predisposes it to compression from inflammation, edema, or trauma. The most commonly accepted mechanism is reactivation of the herpes simplex virus 1 (HSV-1) originating from the geniculate ganglion, resulting in edema and swelling of the facial nerve with consequent compromise. This theory has been supported by the isolation of HSV-1 in the endoneurial fluid of the facial nerve in patients with Bell palsy. Edema has also been observed on magnetic resonance imaging (MRI) and seen in those patients surgically managed with a decompression procedure. Despite this, the relative association of HSV-1 within the facial nerve does not provide the definitive evidence for the etiology of Bell palsy, and there is still uncertainty regarding its pathophysiology.
PREHOSPITAL CONCERNS
The challenge for prehospital providers is when to activate the stroke protocol. Televideo resources such as those used in community paramedicine initiatives may be helpful. When there is doubt, emergency medical service (EMS) systems are best advised to transport to a stroke center.
APPROACH TO THE PATIENT WITH BELL PALSY
The diagnosis of Bell palsy is driven by clinical examination and history, and occurs when no other explanation for the cause of facial weakness has been determined. There is typically little role for imaging or laboratory testing. The examination should include careful assessment of the ability to move the forehead. Forehead movement or sparing suggests a central etiology; however, mild cases of Bell palsy may appear to spare the forehead. Examination of the oropharynx, external canal, and tympanic membranes should be performed to determine whether vesicular lesions are present. The presence of these lesions, which can also be accompanied by sensorineural hearing loss, represents the Ramsay-Hunt syndrome. The chorda tympani nerve, a sensory branch of the facial nerve that courses through the middle ear and supplies taste to the anterior two-thirds of the tongue is also seen in patients with Ramsay-Hunt syndrome.
Patients can present with a constellation of symptoms that vary in severity. Because of inability to close the affected eye, patients may have an ipsilateral dry eye and decreased tear production due to parasympathetic lacrimal gland involvement. Changes in the ability to taste and dry mouth can occur, and patients may have difficulty with handling food and secretions and demonstrate drooling or excessive tearing while eating. Facial and postauricular pain may also be present, often occurring before the onset of facial weakness. Hyperacusis, although less commonly seen, occurs because of loss of function of the stapedius muscle that typically mitigates vibrations in the inner ear and results in sound perceived as unusually loud on the affected side.
The differential diagnosis is divided into multiple etiologies: congenital, endocrine, infectious, traumatic, neoplastic, inherited, neurovascular, idiopathic, and autoimmune categories (see Table 8.1).
Other diagnostic testing, although not routinely recommended on initial presentation, includes the use of CT or MRI to assess the facial nerve, electromyography (EMG), electroneuronography (ENoG), and serologic testing for infectious etiologies.
MANAGEMENT
An algorithmic approach to management is seen in Figure 8.1. The natural history of Bell’s palsy is such that symptoms improve (even without any medical treatment) within 3 to 4 weeks of initial presentation, and complete resolution occurs by 3 months. Patients with prolonged symptoms, although less commonly seen in the acute care setting, should undergo further testing and consideration for an alternative diagnosis. The severity of the paralysis in Bell’s palsy will often determine potential for complete recovery and can be objectively assessed using the House-Brackmann scale, which incorporates visual inspection and motor testing to determine the grade of dysfunction. However, the House-Brackmann scale was not intended for use in the initial evaluation of paralysis in patients with suspected Bell’s palsy, and thus will be of little aid to the emergency clinician.2
The mainstay of treatment in Bell’s palsy is a short course of oral glucocorticoids often as monotherapy, or in combination with antivirals. Antivirals prescribed alone are not recommended. The use of combination therapy is controversial, and the evidence is not clear-cut. We recommend
prednisone, 60 mg/d, for 7 days without a taper. If antivirals are also given, we recommend either valacyclovir, 1000 mg three times a day, or acyclovir, 400 mg five times a day for 7 days. The greatest benefit demonstrated in studies is the administration of glucocorticoids within 72 hours of onset of symptoms, although there is evidence that recovery is improved if medications are started at 48 hours.3 Rates of recovery and reduction of long-term sequelae have been found with the use of steroids alone. The combination of antivirals and steroids as a treatment regimen for Bell’s palsy lacks consensus in the literature.
prednisone, 60 mg/d, for 7 days without a taper. If antivirals are also given, we recommend either valacyclovir, 1000 mg three times a day, or acyclovir, 400 mg five times a day for 7 days. The greatest benefit demonstrated in studies is the administration of glucocorticoids within 72 hours of onset of symptoms, although there is evidence that recovery is improved if medications are started at 48 hours.3 Rates of recovery and reduction of long-term sequelae have been found with the use of steroids alone. The combination of antivirals and steroids as a treatment regimen for Bell’s palsy lacks consensus in the literature.
 Figure 8.1: Clinical decision-making algorithm for acute Bell’s palsy. From de Almeida JR, Guyatt GH, Sud S, et al. Bell Palsy Working Group, Canadian Society of Otolaryngology—Head and Neck Surgery and Canadian Neurological Sciences Federation. Management of Bell’s palsy: clinical practice guideline. CMAJ. 2014;186(12):917-922. |
We recommend offering combination therapy to patients presenting within 72 hours of symptoms or in cases of severe facial nerve dysfunction. Providers should also counsel patients on the current evidence regarding antivirals so there is clear understanding of the uncertainty of their role in treatment of Bell’s palsy. Other proposed treatments such as surgical decompression, physical therapy, and acupuncture have not demonstrated improved outcomes.4,5
Management of associated symptoms and potential sequalae is an important part of the management strategy. With the inability to fully close the eyelid, eye care is required to prevent corneal abrasion, ulceration, or keratitis. Patients should be prescribed artificial tears or eye lubricants and protection with an eye patch while sleeping. These patients will need urgent specialty follow-up with ophthalmology and otolaryngology.
TIPS AND PEARLS
Up to 30% of patients with a Bell’s palsy will have a delayed recovery or not recover full facial function.
Bell’s palsy is more commonly seen in patients with a history of diabetes, hypertension, and in late-term pregnancy. The pathophysiologic mechanisms are thought to be virally mediated.
Bilateral Bell’s palsy is uncommon, and should prompt a workup for other etiologies including Lyme disease, GBS, or sarcoidosis.
Corticosteroids are the mainstay of treatment; and the use of combination therapy with antivirals may be beneficial for long-term sequelae, but lacks strong evidence.
EVIDENCE
Is there an advantage of combination treatment with steroids and antivirals versus steroids alone in the treatment of Bell’s palsy?
The American Academy of Neurology (AAN) evidence-based guidelines in 2012 reviewed the role of steroids and antivirals in the treatment of Bell’s palsy.6 The authors examined the prior 12 years of literature and determined that for patients with new-onset Bell’s palsy, the addition of antivirals might be offered to increase the likelihood of facial nerve recovery (Level C), but that a benefit has not been established. The authors did conclude that oral steroids should be offered, with a high likelihood of improving recovery of facial nerve function (Level A).
The American Academy of Otolaryngology published Clinical Practice Guideline: Bell’s Palsy in 2013 and recommended that antivirals may be offered in addition to steroids if given within 72 hours or for symptoms with Grade B.2 The authors report that this conclusion is not supported by high-quality trials and that a “small benefit cannot be excluded” in light of the low risk of use of antivirals.
The Canadian Society of Otolaryngology published Management of Bell’s Palsy: Clinical Practice Guideline in 2014 and recommended the addition of antiviral therapy to corticosteroids based on severity of the presentation of Bell’s palsy.7 For mild to moderate severity, the authors strongly recommend against the addition of antivirals, and for severe to complete paresis, they recommend the use of combined therapy, but both of these are weak recommendations based on the available evidence.
A Cochrane review from 2019, Antiviral Treatment for Bell’s Palsy examined the role of combination therapy versus corticosteroids alone or combined with placebo.8 The authors included 14 randomized controlled trials (RCTs) in their meta-analysis with a total of 2488 study subjects. The measured outcome criterion in the studies was recovery of facial function based on a scoring system such as House-Brackmann. The conclusions were that combination therapy with antivirals and corticosteroids may have “little or no effect on rates of incomplete recovery in comparison to corticosteroids alone, and there may be no clear difference with the combination therapy compared to corticosteroids alone.” They did report that combination therapy could probably reduce late sequalae of the disease compared with monotherapy with corticosteroids.
Is there a role for surgical decompression in the treatment of Bell’s palsy?
Surgical decompression is a controversial treatment and of questionable benefit for refractory patients, those with poor results from nerve conduction studies, or advanced disease as determined by an assessment using the House-Brackmann scale. Because of the natural history of the disease and spontaneous recovery without treatment, most likely there are limited patients who are surgical candidates.
A Cochrane review from 2013 examined the role of surgical decompression in Bell’s palsy and found only two studies that met criteria for inclusion.4 The authors incorporated two non-blinded RCTs with a total of 69 participants from both studies into the meta-analysis. The outcome was recovery of facial nerve palsy at 12 months. One study evaluated surgery with steroids versus surgery without and demonstrated similar rates of recovery at 9 months. The second study compared surgery versus no treatment and found no differences in recovery at 1 year. The authors concluded both studies were underpowered to detect a difference, and thus there is limited evidence to decide if surgical decompression is safe or harmful in Bell’s palsy.
The American Academy of Otolaryngology published clinical guidelines for the management of Bell’s palsy and provides no recommendation because of the paucity of literature and potential risks of surgery.2
What is the risk of misdiagnosing a central etiology as a Bell palsy and vice versa?
Because Bell’s palsy is a clinical diagnosis with typically no role for invasive testing or imaging, there may be a concern for missing a more dangerous or life-threating diagnosis such as a stroke, subarachnoid hemorrhage, or other life-threatening condition on initial evaluation (Table 8.2).
There is a paucity of literature in this area, but a study from 2014 examined 6 years of administrative claims data from California to determine the incidence and risk factors that might lead clinicians in the emergency department (ED) to make an incorrect diagnosis of Bell’s palsy.9 The outcome measure was a change in the index diagnosis of Bell’s palsy in the ED to a more serious International Classification of Diseases Ninth Revision (ICD-9) discharge or inpatient diagnosis code that included ischemic stroke, intracranial hemorrhage, brain tumor, or other, seen within 90 days of the initial visit. The study identified 365 patients who received one of the alternative diagnoses (0.8%) within 90 days; and when the authors limited this to life-threatening diagnoses, they found a total of 127 patients (0.3%). Patients who were assigned a more serious diagnosis were more likely to have more number of comorbidities, and underwent imaging on initial presentation. Ischemic stroke was the most commonly assigned serious diagnosis, representing 27.5% of the patients, with otitis media or mastoiditis representing 24% and herpes zoster 23.2%. The study was limited because it did not examine granular-level chart data and did not link outpatient visits where another diagnosis could have been assigned. The authors concluded that there is a low rate of misdiagnosis of Bell’s palsy, but emergency clinicians should pay close attention to elderly patients with diabetes.
There is a paucity of literature in this area, but a study from 2014 examined 6 years of administrative claims data from California to determine the incidence and risk factors that might lead clinicians in the emergency department (ED) to make an incorrect diagnosis of Bell’s palsy.9 The outcome measure was a change in the index diagnosis of Bell’s palsy in the ED to a more serious International Classification of Diseases Ninth Revision (ICD-9) discharge or inpatient diagnosis code that included ischemic stroke, intracranial hemorrhage, brain tumor, or other, seen within 90 days of the initial visit. The study identified 365 patients who received one of the alternative diagnoses (0.8%) within 90 days; and when the authors limited this to life-threatening diagnoses, they found a total of 127 patients (0.3%). Patients who were assigned a more serious diagnosis were more likely to have more number of comorbidities, and underwent imaging on initial presentation. Ischemic stroke was the most commonly assigned serious diagnosis, representing 27.5% of the patients, with otitis media or mastoiditis representing 24% and herpes zoster 23.2%. The study was limited because it did not examine granular-level chart data and did not link outpatient visits where another diagnosis could have been assigned. The authors concluded that there is a low rate of misdiagnosis of Bell’s palsy, but emergency clinicians should pay close attention to elderly patients with diabetes.
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