What is the House‑Brackmann scale for grading facial nerve function in Bell’s palsy?

House-Brackmann Grading System for Facial Nerve Function

Overview and Purpose

The House-Brackmann (HB) grading system is a standardized 6-grade scale used to assess facial nerve function in Bell's palsy and other facial nerve disorders, ranging from Grade I (normal function) to Grade VI (complete paralysis). 1, 2

The system was originally developed to quantify facial nerve recovery after surgeries that put the facial nerve at risk, but has been expanded to assess recovery after trauma and conditions like Bell's palsy. 3

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The Six Grades Defined

Grade I: Normal

• Normal facial function in all areas with no visible weakness or asymmetry. 1, 2

Grade II: Mild Dysfunction

• Slight weakness noticeable only on close inspection. 1, 2
• At rest: normal symmetry of forehead. 1
• Ability to close eye with minimal effort and slight asymmetry. 1
• Ability to move corners of mouth with maximal effort and slight asymmetry. 1
• No synkinesis, contracture, or hemifacial spasm. 1

Grade III: Moderate Dysfunction

• Obvious but not disfiguring difference between the two sides with no functional impairment. 1, 2
• At rest: normal symmetry and tone. 1
• Motion: slight to no movement of forehead. 1, 2
• Ability to close eye with maximal effort and obvious asymmetry. 1
• Ability to move corners of mouth with maximal effort and obvious asymmetry. 1
• Patients with obvious but not disfiguring synkinesis, contracture, and/or hemifacial spasm are Grade III regardless of degree of motor activity. 1

Grade IV: Moderately Severe Dysfunction

• Obvious weakness and/or disfiguring asymmetry. 1, 2
• At rest: normal symmetry and tone. 1
• Motion: no movement of forehead. 1, 2
• Inability to close eye completely with maximal effort. 1
• Patients with synkinesis, mass action, and/or hemifacial spasm severe enough to interfere with function are Grade IV regardless of motor activity. 1

Grade V: Severe Dysfunction

• Only barely perceptible motion. 1, 2
• At rest: possible asymmetry with droop of corner of mouth and decreased or absence of nasolabial fold. 1, 4
• Motion: no movement of forehead. 1, 2
• Incomplete closure of eye and only slight movement of lid with maximal effort. 1, 4
• Slight movement of corner of mouth. 1
• Synkinesis, contracture, and hemifacial spasm usually absent. 1

Grade VI: Total Paralysis

• Loss of tone with marked asymmetry. 1, 2
• No motion whatsoever. 1, 2
• No synkinesis, contracture, or hemifacial spasm. 1

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Clinical Applications in Bell's Palsy

The HB system should be used to document baseline facial function at presentation and track recovery over time in Bell's palsy patients. 2

• HB grades I-II are generally considered favorable outcomes. 2
• The scale demonstrates utility in outcome measurement, with surgical decompression studies showing 91% of patients achieving HB grade I/II with surgery versus 42% with steroids alone. 2
• The HB grade should be documented when considering surgical decompression for severe cases, typically those with significant reduction on electroneurography. 2

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Critical Clinical Considerations

Eye Protection Mandate

Immediate eye protection is mandatory regardless of HB grade if incomplete eye closure is present (Grades IV-VI), using lubricating drops, ointment, and eye taping/patching to prevent permanent corneal damage. 1, 2

Limitations of the System

• The HB system was not originally designed to assess initial facial nerve paresis or paralysis of Bell's palsy, though it is commonly used for this purpose. 3
• The numeric portion of the HB grading system is not a useful guide in identifying patients at risk of corneal complications; measurements of lagophthalmos and upper lid closure are more valuable for this purpose. 5
• In patients with differential facial weakness across regions, a single global HB score does not fully communicate facial function and primarily reflects the function of the eye (61% correlation), followed by nose/midface (40%), mouth (32%), and forehead (18%). 6

Alternative Grading Approaches

• The Facial Nerve Grading System 2.0 (FNGS 2.0) incorporates regional scoring of facial movement (forehead, eye, nose, mouth), providing additional information while maintaining agreement comparable to the original HB scale. 7
• FNGS 2.0 shows moderate agreement with HB grading (overall intraclass correlation coefficient 0.908), with exact agreements between regional assessment and FNGS 2.0 for the mouth, eyes, and brow of 72%, 63%, and 52%, respectively. 8
• Regional assessment using the HB scale reported as F(w) E(x) N(y) M(z) more fully communicates facial function in patients with differential weakness. 6

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Practical Clinical Use Algorithm

1. At initial presentation: Document HB grade to establish baseline severity. 2
2. Assess eye closure: If incomplete (Grade IV or higher), immediately implement eye protection measures. 1, 2
3. Follow-up assessments: Re-grade at 3 weeks, 6 weeks, and 3 months to track recovery. 8
4. Consider regional scoring: In patients with differential facial weakness, document function separately for forehead, eye, nose, and mouth. 6
5. Reassessment triggers: Mandatory reassessment or specialist referral for incomplete facial recovery at 3 months. 4