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Bell's palsy: Pathogenesis, clinical features, and diagnosis in adults

Bell's palsy: Pathogenesis, clinical features, and diagnosis in adults
Literature review current through: Sep 2023.
This topic last updated: Sep 12, 2022.

INTRODUCTION — Idiopathic facial nerve palsy, also referred to as Bell's palsy, is the most common type of spontaneous peripheral facial paralysis. A viral etiology (ie, activation of the herpes simplex virus) is suspected in most cases of Bell's palsy, although there is no established or widely available method of confirming a viral mechanism in clinical practice.

This review will discuss the pathogenesis, clinical features, and diagnosis of Bell's palsy. The treatment and prognosis of Bell's palsy are discussed separately. (See "Bell's palsy: Treatment and prognosis in adults".)

The clinical features, diagnosis, and management of facial nerve palsy in children are discussed elsewhere. (See "Facial nerve palsy in children".)

ANATOMY OF THE FACIAL NERVE — The facial nerve is a mixed nerve, containing the following (figure 1) [1]:

Motor fibers that innervate the facial muscles

Parasympathetic fibers innervating lacrimal, submandibular, and sublingual salivary glands

Afferent fibers from taste receptors in the anterior two-thirds of the tongue

Somatic afferents from the external auditory canal and pinna

The course of the facial nerve can be traced from its origin at the facial nucleus in the ventrolateral pons to the peripheral synapses at autonomic ganglia and neuromuscular or neuroglandular junctions in the face. The facial nerve can be divided into distinct anatomic regions.

Intracranial segment – The efferent fibers that will comprise the facial nerve arise from the facial nucleus and the superior salivary nucleus in the ventral pontine tegmentum. The facial nerve is comprised of a motor root and a visceral mixed root known as the nervus intermedius. It courses for approximately 10 mm in length from the brainstem at the pontomedullary junction laterally through the cerebellopontine angle together with the vestibulocochlear nerve. At the internal auditory meatus, the facial nerve becomes encased in periosteum and perineurium.

Fallopian segment – The bony facial (fallopian) canal is bordered by the internal auditory meatus and the stylomastoid foramen. It is approximately 33 mm in length and consists of three consecutive segments: labyrinthine, tympanic, and mastoid. Because the canal is narrowest in the labyrinthine segment (average 0.68 mm in diameter), any swelling of the nerve is likeliest to result in compression here. The nerve runs laterally toward the medial wall of the epitympanic recess where it bends sharply backward. At the bend (or genu) is a swelling, the geniculate ganglion, lying in the labyrinthine segment of the canal. The nerve then passes backward and downward to reach the extracranial surface at the stylomastoid foramen.

Branches of the facial nerve arising within the fallopian segment include:

The greater petrosal nerve branches off the facial nerve at the geniculate ganglion, enters the middle cranial fossa extradurally, and exits through the foramen lacerum toward the pterygopalatine ganglion (figure 1). It supplies the lacrimal and palatine glands.

The nerve to the stapedius is the next branch as the nerve passes downward to the stapedius muscle in the tympanic cavity of the middle ear.

The chorda tympani is the largest branch of the facial nerve and arises from the main trunk of the facial nerve approximately 6 mm above the stylomastoid foramen. The chorda tympani contains secretomotor fibers to sublingual and submandibular glands and visceral afferent fibers for taste. It passes across the tympanic membrane, separated from the middle ear cavity only by a mucous membrane and then joins the main trunk of the facial nerve. The cell bodies of the unipolar afferent gustatory neurons lie in the geniculate ganglion and then travel via the nervus intermedius to the solitary tract nucleus (figure 2).

Extracranial segments – Most of the motor fibers of the facial nerve emerge at the stylomastoid foramen, turn anterolaterally, and pass through the parotid gland. These fibers divide into five groups of nerves between the deep and superficial lobes of the parotid gland at the pes anserinus (Latin "goose foot") and are distributed to the facial muscles in a variable pattern (figure 1).

The cell bodies of the extracranial greater petrosal nerve lie in the pterygopalatine ganglion in the pterygopalatine fossa. Parasympathetic nerve fibers branch to supply lacrimal and palatine glands and portions of the soft palate (figure 2).

The extracranial segment of the chorda tympani continues anteriorly to join the lingual nerve to provide taste to the anterior two-thirds of the tongue. A branch to the submandibular ganglion supplies the submandibular and sublingual glands.

EPIDEMIOLOGY — Bell's palsy, defined as an acute idiopathic peripheral facial nerve palsy, represents approximately half of all cases of peripheral facial nerve palsy [2]. The annual incidence rate is between 13 and 34 cases per 100,000 population [3]. There is no race, geographic, or sex predilection.

The risk is three times greater during pregnancy, especially in the third trimester and in the first postpartum week [4]. Hypertension has been associated with a modestly increased risk of Bell's palsy in some [5,6], but not all [7,8], observational studies. Perineural edema, hypercoagulability causing thrombosis of the vasa nervosum, and relative immunosuppression in pregnancy have been proposed as potential etiologic factors [9]. One study found an association of Bell's palsy in pregnancy with preeclampsia and gestational hypertension [10].

Microvascular damage and inflammation associated with diabetes may account for approximately 5 to 10 percent of patients with Bell's palsy [11,12]. The recurrence rate of Bell's palsy is discussed separately. (See "Bell's palsy: Treatment and prognosis in adults", section on 'Risk of recurrent Bell's palsy'.)

DEFINITION AND PATHOGENESIS — Bell's palsy is the term used to refer to cases of isolated peripheral facial paralysis that are idiopathic [13]. Bell's palsy occurs when inflammation at the facial nerve impairs peripheral function. The facial nerve becomes thickened with an edematous perineurium and diffuse infiltrates of small, round, inflammatory cells between nerve bundles and around intraneural blood vessels. Myelin sheaths undergo degeneration [14]. These changes may be seen throughout the bony course of the facial nerve, although nerve damage is maximal in the narrow labyrinthine part of the facial canal where edema causes nerve compression and the tenuous blood supply adds to the damage. (See 'Anatomy of the facial nerve' above.)

In many cases, herpes simplex virus activation is the suspected cause of Bell's palsy [15,16]. Nevertheless, such patients with peripheral facial palsy are labeled as having Bell's palsy because there is no established or widely available method of confirming herpes simplex virus as the mechanism in clinical practice. However, inflammatory changes that cause facial paralysis may also result from many identifiable causes, including infectious sources. When facial paralysis occurs due to a specific cause or is associated with additional signs or symptoms, the syndrome is named according to the etiology or symptom complex. (See 'Differential diagnosis' below.)

Several suspected sources of inflammation at the facial nerve have been implicated in the pathogenesis of Bell's palsy.

Herpes simplex – Herpes simplex virus activation has become widely accepted as the most frequent cause of Bell's palsy [7,17,18], though the evidence is not entirely conclusive [19,20]. A herpes simplex–mediated viral inflammatory/immune mechanism was the subject of controversy for years but was suspected based upon serologic evidence [21]. Polymerase chain reaction DNA testing supports the notion of axonal spread and multiplication of a reactivated neurotropic virus leading to inflammation, demyelination, and nerve injury. In one study, herpes simplex virus type 1 genomes were identified in facial nerve endoneurial fluid and auricular muscle of 11 of 14 patients with Bell's palsy undergoing decompressive surgery but in no patients undergoing surgery for other indications [22].

Other viral associations – An inflammatory response to other viral infections has also been associated with facial palsy. In a large series of 1701 cases of Bell's palsy, 116 had herpes zoster [7]. Other potential infectious sources of acute peripheral facial palsy include cytomegalovirus, Epstein-Barr virus, adenovirus, rubella virus, mumps, influenza, coxsackievirus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [23-30]. Two cases due to rickettsial infection have also been reported [31], as have cases of ehrlichiosis [32].

Noninfectious mechanisms – Alternate postulated mechanisms of Bell's palsy include facial nerve ischemia [33,34]. A retrospective study found that 190 (74 percent) of 257 patients with Bell's palsy first noticed facial weakness in the morning, suggesting that actual development of facial palsy occurred during sleep [34]; the authors speculated that nocturnal onset suggested an ischemic mechanism. In addition, diabetes has been implicated as a factor in entrapment neuropathies and Bell's palsy by microangiopathy of the vasa nervorum [35].

An immune-mediated inflammatory response to some vaccines have been associated with Bell's palsy. An inactivated intranasal influenza vaccine that was used in 2000 (and since withdrawn from the market) was associated with Bell's palsy in a Swiss case-control study [36]. The peak occurrence of Bell's palsy was between 31 and 60 days after intranasal vaccination, suggesting that the palsy was not due to a direct toxic response but rather an induced immune response, such as reactivation of latent herpes simplex or varicella-zoster virus [37]. Bell's palsy has also been reported following vaccination against the SARS-CoV-2 virus [38-40]. However, the causal role of vaccines is uncertain as the reported case rate may be similar to the background rate of Bell's palsy.

Pregnancy-related fluid retention, most marked in the third trimester and the first postpartum week, may lead to compression of the nerve or perineural edema. Other potential etiologic factors in pregnancy include hypercoagulability causing thrombosis of the vasa nervorum and relative immunosuppression [9]. Several studies have found an association of Bell's palsy with preeclampsia, also suggesting extracellular edema as the mechanism [10,41,42].

A genetic predisposition has been implicated in some cases of Bell's palsy [43-45].

CLINICAL FEATURES — Patients with Bell's palsy typically present with the sudden onset (usually over hours) of facial paralysis. Bell's palsy is also frequently associated with impairment in taste. Some patients may report ipsilateral hyperacusis or decreased tearing of the eye. Specific techniques may be used on clinical examination to identify features of Bell's palsy. (See 'Clinical evaluation' below.)

Bell's palsy has psychological as well as physical effects with facial disfigurement leading to adverse effects on mental health, including anxiety and depression. (See "Bell's palsy: Treatment and prognosis in adults", section on 'Psychological impact'.)

Pattern of facial weakness — Bell's palsy is a peripheral nerve syndrome characterized by weakness of the upper and lower portions of the face. Classic findings include the eyebrow sagging, inability to close the eye, disappearance of the nasolabial fold, and drooping at the affected corner of the mouth, which is drawn to the unaffected side (picture 1).

A history of a facial twitch or spasm that precedes facial weakness suggests nerve irritation from tumor and should prompt imaging [46]. (See 'Tumor' below.)

Symptoms are typically unilateral, but cases of bilateral Bell's palsy may occur. Patients with acute, bilateral facial weakness should be evaluated for Lyme disease and other more common causes of bilateral symptoms. (See 'Differential diagnosis' below.)

Temporal features – Onset of facial weakness in Bell's palsy occurs over several hours, up to 72 hours. Symptoms may worsen for days, up to three weeks, then stabilize to improve. When symptoms occur suddenly or fail to improve at least partially by four months, alternative diagnoses should be considered. (See 'Differential diagnosis' below.)

Examination findings – Facial weakness with Bell's palsy typically involves the upper and lower portions of the face because nerve impairment is typically in the facial canal, proximal to the site where the nerve branches to distinct muscle groups in the face (figure 1). By contrast, central causes of facial weakness due to unilateral upper motor neuron conditions such as stroke or tumor produce facial weakness restricted to the lower portion of the face because nerve branches from the facial nucleus to the eyelid and forehead receive fibers from bilateral corticobulbar fibers.

However, atypical presentations may also be seen in some patients with facial weakness.

Lower facial weakness that spares the eyelid and forehead muscles is usually due to a central lesion but may also be due to a distal peripheral cause. As an example, a partial lesion of the distal facial nerve at the pes anserinus (between the deep and superficial lobes of the parotid gland) that spares the temporal branch to the frontalis muscle results in lower facial paralysis, but the patient is still able to wrinkle the forehead. Nonetheless, cases of facial weakness with forehead sparing should stimulate further evaluation of a possible central etiology. (See 'Differential diagnosis' below.)

Upper and lower facial weakness (that includes weakness of the eyelid and forehead muscles) is usually due to a peripheral lesion such as Bell's palsy but may also be due to a central cause. An ischemic stroke in the ventrolateral pons that involves the ipsilateral facial nerve tract or facial nucleus and distal projections can affect all peripheral facial nerve fibers and may result in upper and lower facial weakness. (See 'Stroke' below.)

Patients with Bell's palsy and other peripheral causes of facial weakness have impairment in volitional movement of facial muscles as well as emotional expression, as in smiling or laughing. Nerve projections from the frontal lobe and elsewhere that are responsible for emotional expression are distinct from pathways controlling volitional movement. Thus, facial weakness with preserved motor control of either emotional or volitional expression suggests a central cause to symptoms [47-49]. (See 'Differential diagnosis' below.)

Sensory and autonomic dysfunction — Sensory dysfunction in Bell's palsy is due to involvement of afferent sensory fibers to the facial nerve. Patients may report ipsilateral impaired taste sensation, decreased tearing and/or salivation, and hyperacusis. The chorda tympani branch carries taste and salivary fibers, the petrosal nerve branches carry lacrimal fibers, and the nerve to the stapedius dampens sound waves and accounts for hyperacusis. Some patients also report a prodrome of ear pain (dysacusis), presumably due to mild dysfunction of or near the nerve to the stapedius.

Sensory and autonomic dysfunction help to site the lesion in the fallopian canal and may be indicators of a more severe course.

Additional cranial neuropathies — Bell's palsy refers to cases of isolated peripheral seventh cranial nerve neuropathy. However, additional cranial neuropathies including a mild ipsilateral trigeminal sensory neuropathy may infrequently occur in patients diagnosed with Bell's palsy after exclusion of alternative causes [50,51]. Local viral or inflammatory spread from the facial nerve to adjacent branches of the maxillary branch of the trigeminal nerve near the sphenopalatine ganglion may account for ipsilateral sensory involvement. In one report of a patient with Bell's palsy, enhancement on magnetic resonance imaging (MRI) was found in both the facial and the adjacent maxillary nerve branches [52]. In addition, ipsilateral sensory loss in the setting of Bell's palsy may also be attributed to abnormal sensory perception due to unilateral weak facial muscles and drooping skin tissue.

Other cranial nerve dysfunctions have also been reported in patients with Bell's palsy. In one prospective case series of 51 patients clinically diagnosed with Bell's palsy, 13 patients had ipsilateral facial sensory impairment suggestive of ipsilateral trigeminal neuropathy [50]. In addition, four presented with additional cranial nerve dysfunction, including contralateral trigeminal, glossopharyngeal, and hypoglossal neuropathies. However, most patients in this series did not undergo diagnostic testing such as lumbar puncture or neuroimaging to exclude other causes to symptoms and follow-up evaluation was limited to telephone interview.

Patients who present with facial palsy and evidence of additional cranial neuropathies should be evaluated for alternative causes to symptoms. (See 'Differential diagnosis' below.)

DIAGNOSTIC EVALUATION

Diagnosis — Bell's palsy should be suspected in patients with acute-onset isolated unilateral facial weakness. The clinical diagnosis is made in patients with typical features (algorithm 1):

Weakness of the face that is unilateral and involves the lower (mouth, cheek) and upper (eye, forehead) muscles, with or without loss of taste on the anterior two-thirds of the tongue or altered secretion of the lacrimal and salivary glands.

Acute onset of symptoms, within one to three days. The course is progressive, reaching maximal clinical weakness/paralysis within three weeks or less from the first day of visible weakness. Recovery of some degree of function occurs within four months.

Laboratory testing for Lyme disease is warranted for patients in areas where the disease is endemic. (See 'Testing for Lyme disease' below.)

Features that are atypical for Bell's palsy include [3,53,54]:

Atypical clinical features

Bilateral acute facial weakness

Additional cranial neuropathies or other neurologic signs

Systemic signs (eg, rash, swelling, cervical adenopathy)

Atypical temporal pattern

Sudden onset of symptoms at maximal severity (ie, no progression)

Insidious onset of symptoms (eg, over weeks to months)

Continued worsening of symptoms beyond three weeks

No improvement in symptoms within four months of onset

Patients with atypical features require diagnostic evaluation to evaluate for other causes for symptoms. (See 'Diagnostic testing for atypical presentations' below.)

Clinical evaluation — Examination of facial weakness includes assessment of the face at rest and with movement. Ipsilateral findings include widening of the palpebral fissure with sagging of the lower eyelid, eyebrow sagging, disappearance of the nasolabial fold, and drooping of the mouth. Assessment of facial movement includes observing the response to command for closing the eyes, elevating the brow, frowning, showing the teeth, puckering the lips, and tensing the soft tissues of the neck to observe for platysma activation (picture 1).

Taste function may be examined by asking the patient to assess the taste of a small sample of sugar (or sugary solution) placed on the anterior aspect of the ipsilateral half of the tongue. A second sample is subsequently placed on the anterior aspect of the contralateral half of the tongue. The patient is asked to compare the taste between sides to identify lateralizing impairment of taste.

The evaluation also includes a general physical and neurologic examination. Particular attention is directed at the external ear to look for vesicles or scabbing (which indicate herpes zoster), for mass lesions within the parotid gland, and for additional findings on neurologic examination. (See 'Differential diagnosis' below.)

Attempting to localize the site of the lesion with tests such as the Schirmer test for lacrimation, stapedial reflex, and evaluation of salivation have only moderate accuracy and are of little practical benefit [55]. Furthermore, in patients studied at surgery, only 6 percent had lesions distal to the geniculate ganglion [56], the site that these tests target.

Testing for Lyme disease — Serologic testing for Lyme disease is recommended for patients with acute-onset facial palsy when there is the possibility of exposure in Lyme-endemic areas, particularly for those with bilateral facial palsy or other clinical manifestations of Lyme disease.

Serologic testing should follow the two-tier strategy, which uses a sensitive enzyme-linked immunosorbent assay (ELISA) or an immunofluorescent assay (IFA) in place of ELISA, followed by a Western blot if the ELISA or IFA is positive or equivocal. (See "Nervous system Lyme disease", section on 'Facial nerve palsy'.)

Repeat testing may be indicated when initial testing is negative for patients suspected to have Lyme disease who present with early cranial neuropathy within the first four to six weeks after infection. Follow-up serology in several weeks is typically diagnostic. Cerebrospinal fluid analysis is of limited utility if Lyme disease is limited to the peripheral nervous system. (See "Diagnosis of Lyme disease" and "Nervous system Lyme disease", section on 'Facial nerve palsy'.)

Diagnostic testing for atypical presentations — Diagnostic evaluation is warranted to exclude alternative causes for patients with features that are atypical for Bell's palsy. (See 'Diagnosis' above.)

For patients with atypical features for Bell's palsy, we suggest initial evaluation with neuroimaging to evaluate for alternative intracranial and extracranial structural causes. Additional testing for atypical presentations is performed when history and clinical evaluation suggests an alternative diagnosis and neuroimaging is nondiagnostic. (See 'Laboratory testing and other investigations' below.)

Imaging studies — Neuroimaging is performed to evaluate for structural causes of facial weakness when clinical features or temporal course are atypical. For most patients undergoing neuroimaging, we suggest MRI of the brain with gadolinium with sequences to assess the facial nerve and parotid gland.

Magnetic resonance imaging – MRI of the brain with sequences to assess the facial nerve and parotid gland can delineate the soft tissue structures and identify inflammation and edema associated with Bell's palsy. It can also identify alternative causes to symptoms such as cerebral infarction or hemorrhage and neoplasm in the brain, facial nerve, or parotid gland [57]. Herpes zoster can be identified by enhancement of the inner ear structures even without a vesicular eruption [58].

Enhancement isolated to the facial nerve is reported in between 57 and 100 percent of patients with Bell's palsy [58]. Mild enhancement of the fallopian segment of the facial nerve may also be found as a normal variant in asymptomatic subjects [59,60].

Absence of enhancement in patients diagnosed with Bell's palsy may be a good prognostic sign [61,62].

Computed tomography – High-resolution computed tomography (CT) of the head and temporal bone with contrast may be performed as an alternative study for patients unable to undergo MRI or when bony pathology is suspected.

Repeat imaging – For patients with acute onset of facial paralysis and negative initial imaging studies who have continued complete flaccid paralysis at seven months, repeat imaging is warranted to evaluate for slow-growing neoplasm.

Laboratory testing and other investigations — Additional testing is typically reserved for patients with atypical presentations of facial weakness when imaging is nondiagnostic and for those who have features suggestive of an alternative cause to symptoms. (See 'Differential diagnosis' below.)

Laboratory investigations for infectious and/or inflammatory conditions are guided by history and examination findings and may include erythrocyte sedimentation rate, high-sensitivity C-reactive protein, and blood cultures.

Lumbar puncture for cerebrospinal fluid analysis may be used to identify meningitis, Guillain-Barré syndrome, or other inflammatory conditions such as sarcoidosis and herpes zoster.

Parotid gland biopsy is warranted for patients with facial paralysis when there is no recovery by seven months and initial and repeat imaging studies have been nondiagnostic [63]. (See 'Imaging studies' above and "Salivary gland tumors: Epidemiology, diagnosis, evaluation, and staging".)

Electrodiagnostic studies — Electrodiagnostic studies are rarely performed for patients diagnosed with Bell's palsy but may be used to assess the severity of facial nerve injury to help determine the prognosis. They may also be used as part of the diagnostic evaluation of patients with facial weakness who also have signs or symptoms of polyneuropathy such as patients with Guillain-Barré syndrome. (See "Guillain-Barré syndrome in adults: Pathogenesis, clinical features, and diagnosis", section on 'Electrodiagnostic studies'.)

Electrodiagnostic testing typically includes nerve conduction studies (NCS) and electromyography (EMG).

NCS of the facial nerve is performed by stimulating the nerve near the parotid and measuring the evoked potential by surface recording electrodes over the orbicularis oculi, nasalis, or lower facial muscles, yielding a compound muscle action potential (CMAP) reflecting activity in the muscles beneath the electrodes.

In the first days after symptom onset, the blink reflex (stimulation of the supraorbital nerve) can confirm the peripheral origin of weakness and assess the degree of axonal conduction block [64,65]. At approximately 10 days after the onset of symptoms, the amplitude of the CMAP on the paralyzed side compared with that on the normal side yields an estimate of the extent of axonal loss [65].

The CMAP value obtained by facial nerve stimulation correlates histologically with the number of degenerating motor neurons; a CMAP value of 10 percent of normal corresponds with a degeneration or loss of 90 percent of the motor axons on that side [66]. In one study, 90 percent degeneration was considered to be a critical value above which recovery was poor; degeneration of greater than 98 percent predicted a very poor result [67]. Recovery was variable with degeneration between 90 and 98 percent and often weakness and synkinesis resulted. In another study, 75 percent was regarded as the critical cutoff [68].

EMG performed on impacted facial muscles at approximately 20 to 30 days after onset may provide confirmation of muscle denervation and the degree of axonal damage [65]. In patients with axonal loss, needle EMG at approximately three months after onset may be used to assess for evidence of subclinical reinnervation from the facial nerve.

EMG may also show some action potentials on active volition, which allows one to conclude that the nerve is still in continuity and has a potential for regrowth.

Nerve excitability threshold testing is an additional electrodiagnostic technique used to guide prognosis by quantifying the electrical current required to produce a threshold response. A critical value of 3.5 milliamperes is reported to correlate with 90 percent degeneration on motor NCS [69] and implies a poor prognosis [70].

DIFFERENTIAL DIAGNOSIS — An acute isolated facial nerve palsy may be caused by a variety of disorders with a presentation similar to Bell's palsy. These include other conditions that can cause peripheral nerve dysfunction such as herpes zoster infection, Lyme disease, otitis media, Guillain-Barré syndrome (GBS), human immunodeficiency virus (HIV) infection, sarcoidosis, Sjögren's disease, or primary and metastatic tumors. In addition, stroke or other central (brain) conditions may produce a "peripheral" pattern of facial weakness mimicking Bell's palsy. (See 'Pattern of facial weakness' above.)

Herpes zoster — Herpes zoster oticus (Ramsay Hunt syndrome) is diagnosed when ear pain and vesicles are found in the external meatus in the setting of a peripheral facial nerve palsy. In addition, herpes zoster infection may occasionally occur without vesicles, a condition known as zoster sine herpete [71,72]. Zoster sine herpete may be misattributed to Bell's palsy in some cases due to shared clinical features [73]. Dermatomal dysesthesia or ear pain may be the only signs that herpes zoster is the etiology of facial weakness [74]. (See "Epidemiology, clinical manifestations, and diagnosis of herpes zoster", section on 'Ramsay Hunt syndrome (herpes zoster oticus)'.)

Lyme disease — Facial nerve palsy is an acute neurologic manifestation and the most common cranial neuropathy associated with Lyme disease. Facial nerve palsy due to Lyme disease may be bilateral and may occur with or without meningitis. Additional findings suggestive of possible Lyme disease include erythema migrans, fatigue, headache, arthralgias, and lymphadenopathy (table 1). The likelihood that Lyme disease is the cause of a seventh nerve palsy diminishes in either nonendemic areas or at a time of year when Lyme disease is not prevalent. (See "Nervous system Lyme disease" and "Epidemiology of Lyme disease".)

Lyme disease is diagnosed by serologic testing and is discussed in detail separately. (See 'Testing for Lyme disease' above and "Diagnosis of Lyme disease".)

Otitis media, mastoiditis, and cholesteatoma — Facial paralysis is a potential complication of otitis media (bacterial infection of the middle ear) and may also occur in the setting of mastoiditis or a cholesteatoma. Diagnosis is made by inspection of the external meatus, periauricular region, and tympanic membrane. Mastoiditis and a cholesteatoma may also be identified on neuroimaging. (See "Chronic otitis media and cholesteatoma in adults".)

Severe infection with osteomyelitis of the petrous ridge of the temporal bone may cause Gradenigo syndrome, characterized as facial nerve palsy along with ipsilateral abducens (sixth) nerve palsy and retroorbital pain. (See "Acute otitis media in adults", section on 'Petrositis (petrous apicitis)'.)

Guillain-Barré syndrome — Facial weakness that is typically bilateral and symmetric may occur in more than half of patients with GBS. GBS is typically identified in patients with facial palsy by symmetric progressive limb weakness, the presence of additional cranial nerve findings, and reduced deep tendon reflexes. However, distinguishing symptoms may be subtle or absent early in the disease course. In addition, uncommon variant forms of GBS may present with prominent facial diplegia but little or no limb weakness. Diagnostic findings for GBS by cerebrospinal fluid (CSF) analysis include elevated protein with a normal white blood cell count, and neuroimaging may show enhancement of multiple cranial nerves. (See "Guillain-Barré syndrome in adults: Pathogenesis, clinical features, and diagnosis".)

HIV infection — HIV infection rarely causes facial palsy or other mononeuropathies but may cause polyneuropathies, typically in patients with severe immunosuppression. Polyneuropathies that include the facial or other cranial nerves may also be related to concomitant infection with herpes zoster, cytomegalovirus, Treponema pallidum, tuberculosis, or lymphomatous meningitis. (See "Polyradiculopathy: Spinal stenosis, infectious, carcinomatous, and inflammatory nerve root syndromes", section on 'Polyradiculopathy in HIV and AIDS'.)

Sarcoidosis — Cranial neuropathies, including peripheral facial nerve palsy, are a frequent manifestation of neurosarcoidosis. The facial nerve palsy can be unilateral or bilateral (simultaneous or sequential) and may be recurrent. Patients with neurosarcoidosis may have additional neurologic manifestations, including optic neuropathy, peripheral neuropathy, cognitive impairment, and neuroendocrine dysfunction. Neurosarcoidosis may be diagnosed by brain MRI showing meningeal or parenchymal enhancement, CSF analysis showing an elevated immunoglobulin G (IgG) index and a mononuclear cell pleocytosis, or serologic testing. (See "Neurologic sarcoidosis".)

Sjögren's disease — Sjögren's disease can cause multiple central or peripheral neurologic manifestations, including facial nerve palsies or other cranial neuropathies, notably trigeminal sensory loss. However, isolated facial nerve palsy due to Sjögren's disease is unusual. Neurologic symptoms may precede the diagnosis of Sjögren's syndrome, but patients typically also have dry eyes, dry mouth, or parotid gland enlargement. (See "Neurologic manifestations of Sjögren's disease".)

Tumor — Neoplastic lesions at the temporal bone, internal acoustic canal, cerebellopontine angle, or parotid gland can compress or infiltrate the facial nerve and cause an ipsilateral weakness of the upper and lower portions of the face. Intracerebral tumors impacting corticobulbar fibers may cause weakness that is typically restricted to the lower portion of the face. Additional findings associated with a facial nerve palsy due to a tumor include:

Facial twitch or spasm (suggesting ongoing facial nerve irritation) prior to or persisting with weakness

Simultaneous unilateral hearing loss

Parotid mass

Weakness restricted to one or two motor branches of the facial nerve (figure 1)

Slowly progressive or relapsing course of facial weakness

Persistent paralysis with no recovery >4 months from onset

Leptomeningeal metastases from various solid tumors may cause facial and other cranial neuropathies. Primary tumors that may cause facial nerve palsy include schwannoma of the facial nerve and parotid gland tumor. (See "Clinical features and diagnosis of leptomeningeal disease from solid tumors", section on 'Cranial neuropathies' and "Vestibular schwannoma (acoustic neuroma)" and "Salivary gland tumors: Epidemiology, diagnosis, evaluation, and staging".)

Stroke — Facial weakness due to ischemic stroke or intracerebral hemorrhage that involves motor pathways typically presents as mouth drooping but spares the forehead and eyelid muscles. However, a stroke that affects the ipsilateral facial nerve nucleus or facial nerve tract in the pons can cause facial weakness of the upper (forehead and eyelid muscles) and lower (mouth) muscles that mimics Bell's palsy. (See 'Pattern of facial weakness' above.)

In addition to forehead-sparing weakness, onset of facial weakness due to stroke is typically sudden and may be associated with additional neurologic signs.

Melkersson-Rosenthal syndrome — The Melkersson-Rosenthal syndrome is a rare condition with a female predominance characterized by recurrent episodes of facial paralysis, episodic facial swelling, and a trifid fissured tongue [75,76]. Age at onset varies from early childhood to late adulthood. Incomplete forms of this syndrome outnumber those with the classic triad. Granulomatous inflammation is seen in the edematous tissue [77,78]. A genetic origin has been suggested, but the cause is unknown and treatment unproven [79,80].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Bell's palsy".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or email these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

Basics topic (see "Patient education: Bell's palsy (The Basics)")

Beyond the Basics topic (see "Patient education: Bell's palsy (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

Definition and pathogenesis – Bell's palsy is the term used to refer to cases of isolated peripheral facial paralysis not attributed to a specific cause. Herpes simplex virus activation is the suspected cause of Bell's palsy in most cases, but there is no established method to confirm this in clinical practice. (See 'Definition and pathogenesis' above.)

Clinical features – Bell's palsy is a peripheral nerve syndrome characterized by weakness of the upper and lower portions of the face. Classic findings include eyebrow sagging, inability to close the eye, disappearance of the nasolabial fold, and drooping at the affected corner of the mouth, which is drawn to the unaffected side (figure 1 and picture 1). Associated manifestations may include decreased tearing, hyperacusis, and/or loss of taste sensation on the anterior two-thirds of the tongue. (See 'Clinical features' above.)

Diagnosis – The clinical diagnosis of Bell's palsy is made in patients with typical clinical and temporal features (algorithm 1). These features include (see 'Diagnosis' above):

Weakness of the face that is unilateral and involves the lower (mouth, cheek) and upper (eyelid, forehead) facial muscles.

Acute onset of symptoms, within one to three days. The course is progressive, reaching maximal clinical weakness/paralysis within three weeks or less from the first day of visible weakness. Recovery of some degree of function occurs within four months.

Limited diagnostic testing includes laboratory testing for Lyme disease for patients in endemic areas. Additional testing is reserved for patients with atypical clinical features. (See 'Testing for Lyme disease' above and 'Diagnostic testing for atypical presentations' above.)

Atypical features that warrant diagnostic testing – Atypical clinical features include bilateral facial weakness, associated cranial neuropathies or other neurologic signs, and systemic signs such as rash or swelling. Atypical temporal features include facial weakness that is sudden in onset, shows either no progression or progresses after onset for >3 weeks, or does not show improvement within 4 months. (See 'Diagnosis' above.)

Testing for atypical presentations – For patients with atypical presentation of facial weakness, we suggest MRI of the brain with gadolinium contrast to evaluate for intracranial and extracranial structural causes. (See 'Imaging studies' above.)

Additional serologic testing, electrodiagnostic studies, cerebrospinal fluid analysis, and other investigations are typically reserved for patients with atypical presentations of facial weakness when imaging is nondiagnostic and for those who have features suggestive of an alternative cause to symptoms. (See 'Laboratory testing and other investigations' above and 'Electrodiagnostic studies' above.)

Differential diagnosis – An acute isolated facial nerve palsy may be caused by a variety of disorders with a presentation similar to Bell's palsy. These include herpes zoster infection, Lyme disease, otitis media, Guillain-Barré syndrome, HIV infection, sarcoidosis, Sjögren's disease, primary and metastatic tumors, and stroke. (See 'Differential diagnosis' above.)

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Topic 5281 Version 29.0

References

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