Bell Palsy

Bell palsy is an acute, unilateral, peripheral facial nerve palsy of unknown etiology, characterized by rapid-onset weakness of the muscles of facial expression. It is the most common cause of acute facial paralysis, with an annual incidence of 20 to 30 cases per 100,000 persons ^[5]A1c. The condition is named after Sir Charles Bell, a Scottish anatomist who first described the facial nerve's role in facial expression.

Also Known As

• Idiopathic facial nerve palsy
• Idiopathic facial paralysis
• Facial nerve palsy (Bell palsy specifically)
• Cold palsy (historical, reflecting early belief that cold exposure triggered it)

Classification of Severity

Facial nerve function in Bell palsy is most commonly graded using the House-Brackmann grading system (HBGS), a five-point scale (I-VI) that assesses facial symmetry and voluntary motion at rest and with movement. A validated modification, May's classification, collapses HBGS into three functional outcomes: complete recovery (HBGS I), fair recovery (HBGS II-III), and failed recovery (HBGS IV-VI) ^[1]A1a.

Clinical Significance

Bell palsy accounts for approximately 75% of all acute peripheral facial palises and, while often self-limiting, leads to significant functional impairment and psychosocial distress during the acute phase. Timely recognition is critical because outcomes improve with early corticosteroid therapy: treatment with prednisolone 1 mg/kg/day (max 60 mg) for 10 days increases the rate of complete recovery at 3 months from 70% to 85% (number needed to treat [NNT] = 7) ^[5]A1c.

Pearl: Bell palsy is a diagnosis of exclusion defined by idiopathic acute unilateral peripheral facial weakness; severity is graded with the House-Brackmann scale (I-VI), and early prednisolone 1 mg/kg/day for 10 days is standard care (NNT = 7 for complete recovery at 3 months) ^[5]A1c.

The facial nerve's intratemporal course, from the internal auditory meatus through the fallopian canal to the stylomastoid foramen, renders it uniquely vulnerable to compression and ischemia in Bell palsy. The nerve is encased in a bony canal that is narrowest at the labyrinthine segment (mean diameter 0.68 mm), where even mild edema can critically impair microcirculation and axonal transport ^[8]B2b. This anatomical bottleneck explains why the labyrinthine segment is the most common site of nerve swelling and subsequent degeneration in acute palsy.

Segmental Anatomy and Pathological Changes

The facial nerve is divided into five segments: intracranial, meatal, labyrinthine, tympanic, and mastoid. The labyrinthine segment, measuring only 4-5 mm in length, is the most constricted and is the primary locus of entrapment. In Bell palsy, histopathological studies from animal models (rat ligation model) demonstrate that sustained compression leads to intraneural fibrosis, demyelination, and axonal degeneration within 1-3 weeks of onset ^[8]B2b. The degree of fibrosis correlates with the timing of decompression: earlier intervention (within 1 week) reduces fibrotic changes and improves nerve regeneration ^[8]B2b.

Morphological Alterations in Distal Targets

Beyond the nerve trunk, Bell palsy induces morphological changes in the peripheral structures it innervates. The chorda tympani branch, which carries taste fibers to the anterior two-thirds of the tongue, undergoes retrograde degeneration that alters the morphology of fungiform papillae. In patients with unilateral Bell palsy, bilateral examination of the anterior tongue reveals atrophy of fungiform papillae and vascular changes (e.g., reduced capillary density) on both the affected and contralateral sides, suggesting subclinical bilateral involvement of the facial nerve ^[6]B2b. These morphological changes correlate with electrogustometric thresholds and chemogustometry scores, indicating that taste bud structure is directly affected by nerve injury ^[6]B2b.

Cortical Correlates of Nerve Injury

Although not a direct component of the facial nerve's gross structure, the primary motor cortex (M1) contralateral to the paretic face undergoes measurable morphometric changes during recovery. Longitudinal voxel-based morphometry in a single patient showed an initial increase in gray matter concentration in the face area of M1, followed by normalization as motor function returned ^[7]C4. This cortical plasticity reflects the peripheral nerve's structural insult and subsequent reorganization.

Pearl: The labyrinthine segment's bony confinement makes it the epicenter of nerve injury in Bell palsy; early decompression within 1 week reduces intraneural fibrosis and improves axonal regeneration, while bilateral taste bud atrophy underscores subclinical nerve involvement ^[6]B2b[8]B2b.

The facial nerve (CN VII) emerges from the brainstem at the pontomedullary junction, immediately lateral to the abducens nerve (CN VI) and medial to the vestibulocochlear nerve (CN VIII). This cisternal segment (approximately 23 mm long) courses anterolaterally across the cerebellopontine angle cistern, sandwiched between the anterior inferior cerebellar artery (AICA), which loops around the nerve in 64% of individuals, and the choroid plexus of the fourth ventricle ^[9]D5[10]B3b. The nerve then enters the internal acoustic meatus, where it occupies the anterosuperior quadrant, with CN VIII posterior and the nervus intermedius (the nerve's sensory and parasympathetic root) interposed between them.

Intratemporal Course and Key Landmarks

The meatal segment (8-12 mm) gives way to the labyrinthine segment (3-5 mm), the narrowest and most vulnerable portion of the fallopian canal. Here the nerve lies directly beneath the geniculate ganglion, a key surgical and imaging landmark visible on high-resolution CT as a lucent depression in the petrous bone ^[10]B3b. The tympanic segment (11 mm) runs horizontally along the medial wall of the middle ear, just superior to the oval window and cochleariform process; dehiscence of the bony canal occurs in 10-25% of temporal bones, placing the nerve at risk during middle-ear surgery. The mastoid segment (13-16 mm) descends vertically, passing between the facial recess and the fossa incudis before exiting the skull base through the stylomastoid foramen ^[9]D5[10]B3b.

Extratemporal Relations

After exiting the stylomastoid foramen, the nerve turns anteriorly to enter the parotid gland, where it bifurcates into upper (temporofacial) and lower (cervicofacial) divisions. This extratemporal segment (15-20 mm) lies superficial to the stylohyoid and posterior belly of the digastric muscle, a reliable surgical landmark for locating the main trunk during parotidectomy or nerve repair ^[9]D5. The nerve's intimate relation with the parotid parenchyma explains why parotid tumors, abscesses, or iatrogenic injury during gland surgery produce ipsilateral facial weakness. Within the parotid, five terminal branches (temporal, zygomatic, buccal, marginal mandibular, and cervical) emerge and arborize across the superficial musculoaponeurotic system (SMAS), each supplying defined territories ^[9]D5[10]B3b.

Surgical and Imaging Correlates

Pearl: The labyrinthine segment's bony fallopian canal is the narrowest (0.68 mm diameter) and lacks a paraneural sheath, making it the most common site of entrapment edema in Bell palsy, explaining why early decompression at this site may improve recovery in select candidates ^[9]D5[10]B3b.

Arterial Supply of the Facial Nerve

The facial nerve (CN VII) is supplied along its course by three principal arterial systems, making it vulnerable to ischaemia at watershed zones. Within the internal auditory meatus, the labyrinthine artery (a branch of the anterior inferior cerebellar artery, AICA) supplies the nerve. The geniculate ganglion and the horizontal (tympanic) segment receive blood from the superior petrosal branch of the middle meningeal artery. The mastoid and extratemporal segments are perfused by the stylomastoid artery, a branch of the posterior auricular artery (occasionally from the occipital artery) ^[11]D5. This segmental supply creates a critical watershed at the geniculate ganglion, a site where oedema in Bell palsy can precipitate nerve compression and ischaemic injury.

The stylomastoid artery enters the stylomastoid foramen with the facial nerve and anastomoses with the superior petrosal branch, forming a longitudinal plexus along the fallopian canal. Venous drainage parallels the arterial supply, emptying into the pterygoid plexus, the sigmoid sinus, and the superior petrosal sinus via the vein of the cochlear aqueduct.

Venous Drainage and the Role of Venous Congestion

Venous drainage of the facial nerve within the fallopian canal depends on the stylomastoid vein, which drains into the retromandibular vein and the external jugular system. The bony, inextensible fallopian canal means that any increase in venous pressure (e.g., from inflammation, thrombosis, or external compression) can rapidly impair perfusion, contributing to the oedema-ischaemia cycle that is hypothesised in the pathogenesis of Bell palsy ^[6]B2b. There is no dedicated lymphatic drainage within the intratemporal facial nerve; lymph from the surrounding temporal bone drains to the parotid and retropharyngeal nodes, which are therefore relevant only when the differential includes neoplastic or infectious facial nerve involvement.

Innervation of the Nerve's Own Vasa Nervorum

The extrinsic and intrinsic blood vessels of the facial nerve are innervated by sympathetic fibres from the superior cervical ganglion, which travel with the external carotid artery plexus. These vasomotor fibres regulate perfusion pressure within the vasa nervorum; any interruption, such as from viral neuritis or surgical manipulation, can cause local ischaemia. The absence of parasympathetic innervation to the vasa nervorum means that vasodilation is limited, further predisposing the nerve to ischaemic injury during episodes of oedema.

Lymphatic Drainage and Its Clinical Relevance

The parotid gland, through which the extratemporal facial nerve passes, contains a rich lymphatic network. The superficial parotid nodes receive lymph from the lateral face and the external ear, while the deep parotid nodes drain into the upper deep cervical chain (level II). In Bell palsy, these nodes are not typically enlarged; their palpation or pathological enlargement should prompt a search for an alternative diagnosis (e.g., parotid malignancy, sarcoidosis, or tuberculous lymphadenitis ).

Pearl: The facial nerve's segmental blood supply creates a watershed at the geniculate ganglion, a site exquisitely vulnerable to ischaemia when oedema raises intratemporal pressure; lack of a dedicated intratemporal lymphatic network means that any palpable lymphadenopathy in Bell palsy should prompt urgent evaluation for alternative causes such as parotid tumour or sarcoidosis ^[6]B2b[11]D5.

The histology of the involved facial nerve in Bell palsy is defined by an inflammatory demyelinating process centered on the intratemporal segment, particularly the labyrinthine and geniculate portions ^[15]C4. Biopsy and autopsy specimens reveal perivascular and interstitial mononuclear cell infiltration, predominantly lymphocytes and macrophages, surrounding nerve bundles. Edema within the tight osseous confines of the fallopian canal contributes to secondary axonal compression and Wallerian degeneration distal to the site of inflammation.

Key Histopathological Findings

• Demyelination: Segmental loss of myelin sheaths is the earliest change, visible on Luxol fast blue (LFB) staining as pale, disrupted blue rings around axons. Macrophages engulf myelin debris, seen as periodic acid-Schiff ( PAS )-positive granules within foamy cytoplasm.
• Edema and congestion: Endoneurial edema separates individual nerve fibers. The surrounding epineurium may show capillary dilation and red blood cell extravasation, though frank hemorrhage is rare.
• Chronic changes: In patients with incomplete recovery (>3 months), the nerve may exhibit endoneurial fibrosis, decreased axon density (visible on Bielschowsky silver stain), and occasional regenerating clusters (small, thinly myelinated axons grouped together).

Staining Profile

Differential Histology

• Ramsay Hunt syndrome (varicella-zoster virus): Ganglionitis with intranuclear eosinophilic inclusion bodies (Cowdry type A) in satellite cells; positive VZV PCR on nerve tissue or vesicular fluid.
• Lyme neuroborreliosis: Perineural lymphoplasmacytic infiltration with spirochetes visible on modified Dieterle silver stain; positive Borrelia PCR on CSF.
• Sarcoidosis: Non-caseating granulomas with epithelioid histiocytes surrounding nerve fascicles; elevated serum angiotensin-converting enzyme.

Pearl: The histologic hallmark of Bell palsy is a sporadic, monophasic, immune-mediated demyelinating neuritis confined to the intratemporal facial nerve, without viral inclusions or granulomas; the absence of these features helps exclude Ramsay Hunt syndrome and sarcoidosis ^[15]C4.

The seventh cranial nerve develops from the second branchial arch (hyoid arch) during the fourth week of gestation ^[20]D5. Its motor nucleus forms in the caudal pons, while the nervus intermedius, carrying taste from the anterior two-thirds of the tongue and parasympathetic fibers to the submandibular, sublingual, and lacrimal glands, originates from the adjacent geniculate ganglion, itself derived from the epibranchial placode ^[20]D5.

Key developmental steps

By the fifth to sixth week, the facial nerve motor fibers exit the brainstem and course toward the second arch mesenchyme. The nerve becomes closely associated with the stapedius muscle and the posterior belly of the digastric, both arch-derived, and its extratemporal branches arborize to supply the muscles of facial expression ^[20]D5. The chorda tympani, a branch of the nervus intermedius, joins the lingual nerve (mandibular division of CN V) at week 7, reflecting its second-arch gating to the tongue ^[20]D5.

The fallopian canal

The bony fallopian canal (canalis nervi facialis) ossifies from the otic capsule of the temporal bone beginning at week 16 and remains incomplete at birth; its slow postnatal maturation may contribute to the nerve's vulnerability to compression during inflammation, such as in Bell palsy ^[20]D5. The narrowest segment of the canal, the labyrinthine segment, with a diameter of 0.68 mm in adults, is the most common site of entrapment in idiopathic palsy ^[20]D5.

Congenital implications

Developmental arrest or aberrant migration can produce Möbius syndrome (agenesis of the facial nucleus with lateral gaze palsy), Duane retraction syndrome (co-contracting lateral rectus), or isolated unilateral lower lip palsy (congenital absence of depressor anguli oris) ^[20]D5. These must be distinguished from perinatal-acquired Bell palsy, which typically spares the forehead and resolves spontaneously ^[19]B2b.

Pearl: The facial nerve's long intrapetrous course within the fallopian canal, the narrowest segment measuring approximately 0.68 mm, is a consequence of its second-arch embryology and ossifying encapsulation by the otic capsule, explaining both idiopathic palsy and congenital synkinesis ^[20]D5.

Aberrant facial nerve regeneration after Bell palsy produces a spectrum of synkinetic and spasmodic phenomena that are both diagnostically and therapeutically important. These anomalies are not true anatomical variants at baseline but are acquired functional reorganizations following nerve injury; they affect up to 30-40% of patients with incomplete recovery and can mimic or coexist with other neurological disorders.

Synkinesis Patterns

Synkinesis, involuntary contraction of one muscle group triggered by volitional movement of another, is the hallmark of aberrant regeneration. Three common patterns predominate:

• Ocular-oral synkinesis: eye closure triggers mouth corner elevation or narrowing of the palpebral fissure (Marin-Amat syndrome: involuntary eyelid closure upon jaw opening) 22 .
• Oral-ocular synkinesis: mouth movement (e.g., smiling, puffing cheeks) provokes ipsilateral eyelid closure 21 .
• Ptosis with synkinesis (pseudoptosis): the eyelid droops in primary gaze but actually elevates on attempted eye closure because the levator is paradoxically activated 21 . True ptosis must be distinguished from this pseudoptosis.

Hemifacial Spasm and Pain Syndromes

Rarely, aberrant regeneration produces hemifacial spasm, involuntary, unilateral, synchronous contractions of facial muscles, typically accompanied by severe neuropathic otalgia (burning, allodynic pain) and vertigo. This triad (facial weakness → otalgia → hemifacial spasm) has been reported in patients with underlying rheumatic disease, especially Sjögren syndrome and rheumatoid arthritis 26 . The mechanism is thought to involve ephaptic cross-talk at sites of demyelination and aberrant sprouting within the facial nerve trunk or its branches.

Diagnostic Tools and Management

Botulinum toxin remains the first-line pharmacotherapy for all synkinesis variants, with low doses (1.25-5 U Botox) into the target orbicularis oculi muscle producing improvement lasting 3-4 months 25 . For patients refractory to injections, epineurectomy of the facial nerve trunk has shown benefit in reducing oral-ocular and oculo-oral synkinesis in small case series; the procedure targets aberrant connections identified by preoperative ultrasonography and intraoperative abnormal muscle response monitoring 24 . Alternatively, focal resection of the preseptal orbicularis oculi muscle (sparing the pretarsal and orbital portions) treats synkinetic eyelid closure without compromising voluntary eye closure 22 .

Infection-Associated Variations

SARS-CoV-2 infection has been temporally associated with Bell palsy and its anomalous sequelae. In a Sri Lankan surveillance study, Bell palsy was the most common neurological disorder among COVID-19 -associated neurological presentations, with some patients developing persistent synkinesis during recovery 23 . Whether the pandemic strain of SARS-CoV-2 produces a distinct pattern of aberrant regeneration remains unknown, but clinicians should maintain vigilance for atypical post-viral facial nerve anomalies.

Pearl: Synkinesis and pseudoptosis after Bell palsy are often mistaken for new neurological disease; a careful history, noting that involuntary movements occur only with voluntary facial actions, and low-dose botulinum toxin injections (1.25-5 U) into the involved orbicularis oculi muscle provide both confirmatory diagnosis and effective therapy in most patients 21, 25 .

Surface Landmarks

The facial nerve exits the skull base at the stylomastoid foramen, a bony aperture located between the mastoid process and the styloid process. From there, it courses anteriorly into the parotid gland, where it divides into its five terminal branches (temporal, zygomatic, buccal, marginal mandibular, and cervical). Palpation of the mastoid tip and the angle of the mandible provides a surface guide to the nerve's extracranial course. In Bell palsy, tenderness over the stylomastoid foramen may be present, but this finding is neither sensitive nor specific ^[27]B2b.

Imaging Modalities

Contrast-enhanced magnetic resonance imaging (MRI) of the internal auditory canal and facial nerve is the imaging modality of choice when secondary causes are suspected ^{[27]B2b[29]B2b}. High-resolution T1-weighted sequences with fat suppression after gadolinium administration best demonstrate nerve enhancement. Computed tomography (CT) is reserved for evaluating bony anatomy (e.g., temporal bone fractures, cholesteatoma ) and is not routinely indicated for Bell palsy ^[27]B2b.

MRI Findings in Bell Palsy

In acute Bell palsy (within 7 days of symptom onset), contrast-enhanced MRI reveals abnormal enhancement of the affected facial nerve in 85% to 90% of patients ^[29]B2b. The enhancement most commonly involves the geniculate ganglion, followed by the labyrinthine and tympanic segments ^[29]B2b. The intracanalicular segment may also enhance. This pattern reflects inflammation and breakdown of the blood-nerve barrier. However, enhancement is not pathognomonic; it can occur in other inflammatory, neoplastic, or infectious conditions (e.g., Ramsay Hunt syndrome, schwannoma, sarcoidosis) ^{[27]B2b[29]B2b}.

Role of Imaging in Differential Diagnosis

Routine MRI for all patients with Bell palsy is not recommended because the yield of alternative diagnoses is low (1.7% in a large multicenter study) ^[27]B2b. Imaging is indicated when:

• Atypical features are present (e.g., bilateral palsy, recurrent palsy, slow progression >3 weeks, other cranial neuropathies )
• No improvement occurs after 3 months of conservative therapy
• Suspicion of secondary causes such as Ramsay Hunt syndrome (vesicles in the ear canal), temporal bone fracture, parotid tumor, or intracranial mass (e.g., hemangioma, ganglion cyst) ^[28]C4[30]C4

In children presenting with acute facial palsy, the differential includes stroke; MRI with diffusion-weighted imaging can distinguish ischemic stroke from Bell palsy ^[19]B2b.

Pearl: In acute Bell palsy, contrast-enhanced MRI shows facial nerve enhancement in up to 90% of cases, but the diagnosis remains clinical; imaging is reserved for atypical presentations or failure to improve, where it identifies an alternative cause in fewer than 2% of patients ^{[27]B2b[29]B2b}.

Examination Findings and Diagnostic Maneuvers

The classic presentation, acute onset of unilateral lower motor neuron facial weakness, is a clinical diagnosis. On inspection, the brow is flattened, the nasolabial fold is effaced, and the corner of the mouth droops. Ask the patient to raise both eyebrows, close the eyes tightly, puff the cheeks, and show the teeth. In Bell palsy, the forehead is involved (unlike in upper motor neuron weakness from stroke, where the forehead is spared). The palpebral fissure is wider on the affected side, and the eye may not close fully (lagophthalmos), placing the cornea at risk for exposure keratopathy ^[31]A1c.

Red Flags and Stroke Mimics

Bell palsy is the most common stroke mimic in both adults and children ^[16]A1c. Any patient presenting with acute facial weakness must be rapidly assessed for central (upper motor neuron) signs. Key distinguishing features: forehead sparing, isolated lower-face weakness, arm or leg drift, speech disturbance, or acute headache with vomiting point to stroke, not Bell palsy ^[16]A1c. In children, seizures with postictal paralysis and complicated migraine also mimic Bell palsy; imaging (CT or MRI) is indicated when the history or neurological examination is atypical ^[16]A1c.

Phenotypic Variants and Syndromes

Electrophysiological Testing and Prognostication

Electroneuronography (ENoG) and needle electromyography (EMG) provide objective prognostic data. A compound muscle action potential (CMAP) amplitude ≤10% of the unaffected side (denervation ≥90%) within the first 14 days correlates with poor recovery and may prompt consideration of surgical decompression ^[1]A1a. Voluntary motor unit potentials on needle EMG within the first 10 days portend a favorable outcome. Recovery begins within the first 3 weeks in 85% of patients; if no improvement by 4 months, the chance of complete return to normal is low ^[31]A1c.

Corticosteroid Therapy Evidence

Oral prednisolone 1 mg/kg/day (maximum 60-80 mg/day) for 7 days (no taper needed) is the standard of care ^[32]A1a. A network meta-analysis found no significant difference in recovery between oral prednisolone and single-dose intravenous methylprednisolone (OR 1.07, 95% CI 0.81-1.42) ^[32]A1a. In children, a randomized trial showed that at 6 months, 98% of children treated with prednisolone had recovered vs 93% with placebo (absolute difference 5%, NNT = 20, not statistically significant; 95% CI for difference -1% to 12%) ^[35]A1b. Short-course corticosteroids are generally well-tolerated in children; a meta-analysis found that the risk of vomiting was increased (RR 2.18, 95% CI 1.06-4.50, NNH = 14), but serious adverse events were rare ^[18]A1a.

Antiviral Therapy: Limited Role

Antiviral therapy alone (acyclovir or valacyclovir ) is not superior to placebo for recovery ^[34]A1a. Adding antivirals to steroids yields a marginal benefit only in severe Bell palsy (House-Brackmann grade IV-VI). A network meta-analysis of 11 trials (3393 patients) reported that the combination of corticosteroids plus an antiviral improved the odds of complete recovery at 3 months vs steroids alone (OR 1.48, 95% CI 1.02-2.14, NNT = 12) ^[34]A1a. For Ramsay Hunt syndrome, the combination is clearly indicated. Routine monotherapy with antivirals for idiopathic Bell palsy is not recommended ^[31]A1c.

Surgical Decompression: Narrow Indication

Facial nerve decompression (FND) is controversial and rarely performed. In a meta-analysis of 7 studies, the odds of complete recovery (House-Brackmann grade I) after FND vs conservative management was OR 4.7 (95% CI 1.4-16.4), but the evidence is limited by small sample sizes, selection bias, and the natural recovery rate of 85% ^[1]A1a. Current guidelines reserve FND for patients with complete paralysis (House-Brackmann grade VI) and >90% degeneration on ENoG within 14 days of onset, and only if performed within 2-3 weeks of symptom onset ^{[1]A1a[31]A1c}. Beyond this window, decompression offers no benefit over spontaneous recovery ^[31]A1c.

Adverse Events and Vaccine Associations

Short-course corticosteroids are safe. In a systematic review of 30 RCTs (9420 children), short-term corticosteroids (≤14 days) were not associated with serious infections or growth suppression ^[18]A1a. However, Bell palsy has been reported as an adverse event after vaccination, particularly with the tozinameran (BNT162b2) SARS-CoV-2 vaccine. A meta-analysis of 9 studies found a modestly increased risk: incidence rate ratio 2.50 (95% CI 1.30-4.80) for mRNA vaccines compared to unvaccinated controls ^[33]B2a. The absolute risk is low, approximately 0.5 to 1 cases per 10,000 vaccine recipients, and the natural incidence of Bell palsy is 15-30 per 100,000 per year ^[33]B2a.

Eye Protection

Lagophthalmos requires immediate corneal protection. Prescribe artificial tears (preservative-free, every 1-2 hours while awake) and a lubricating ointment at bedtime. Tape the eye closed at night or use a moisture chamber. If corneal exposure persists, consider a temporary tarsorrhaphy or botulinum toxin injection to induce protective ptosis ^[31]A1c.

Pearl: Bell palsy is a clinical diagnosis of exclusion, confirm that forehead muscles are involved (lower motor neuron), document the House-Brackmann grade, start prednisolone 1 mg/kg/day within 72 hours of onset, protect the eye, and reserve antivirals for severe cases or Ramsay Hunt syndrome; routine imaging is unnecessary if the history and exam are classic ^{[16]A1c[31]A1c[32]A1a[34]A1a}.

The eponym "Bell palsy" honors Sir Charles Bell (1774-1842), the Scottish anatomist who first described the clinical features of acute peripheral facial nerve paralysis ^[17]D5. The condition is also referred to as idiopathic facial nerve palsy or acute peripheral facial palsy , terms that emphasize the unknown etiology and the anatomical localization. The possessive form "Bell's palsy" remains common in patient communication and older literature, but contemporary medical writing increasingly uses the non-possessive "Bell palsy" to align with standard eponym conventions ^[17]D5.

Synonyms and Preferred Terminology

Diagnostic Pitfall

The eponym is frequently misapplied to any acute facial paralysis. However, Bell palsy is a diagnosis of exclusion; the term should be reserved for idiopathic cases after ruling out stroke, Ramsay Hunt syndrome, Lyme disease , and other structural causes ^[38]D5. Erroneous use of the eponym can delay appropriate workup and treatment ^[38]D5.

Pearl: The eponym "Bell palsy" should be used only for idiopathic acute peripheral facial nerve palsy after excluding alternative etiologies; the non-possessive form is preferred in current medical literature ^[17]D5[38]D5.