Organización del conocimiento

David H. Chi, MD

Introduction Anatomy History

Physical Examination Pathophysiology

Diagnostic Testing Differential Diagnoses

Bell Palsy Otitis Media

Herpes Zoster Oticus (Ramsay Hunt Syndrome)

Lyme Disease

Melkersson-Rosenthal Syndrome

Kawasaki Disease Trauma

Tumors

Neonatal Facial Paralysis Chronic Facial Paralysis Conclusion

Chapter 3: Facial Paralysis

■

■ Introduction

Facial paralysis is a significant condition because of its cosmetic and functional effects. The physical inability to move a side of the face is very apparent and difficult to disguise. Moreover, facial motion is essential for ocular protection. Secondary corneal injury from drying may occur because of inability to close the eye. Speech and emotional expression may also be affected. The challenge for physicians is to deter-mine the extent of injury, identify the cause of the disorder, and decide whether medical or surgical intervention is required.

■

■ Anatomy

Basic knowledge of the anatomy and function of the facial nerve is essential in understanding facial paralysis. The nerve carries fibers for many different functions. The main function is from the special visceral efferent fibers that supply motor innervation to the facial musculature as well as to the stapedius, posterior belly of the digastric, and stylo-hyoid muscles. Special visceral afferent fibers provide the sensation of taste to the anterior two-thirds of the tongue and hard palate. General visceral efferent fibers function to provide parasympathetic innervation to the lacrimal, submandibular, and sublingual glands. General somatic afferent fibers provide cutaneous sensory innervation to the skin of the concha and small area behind the ear.

■

■ History

A thorough history is essential in evaluating children with facial paralysis. Important information includes the duration and onset of paralysis (eg, sudden, gradual). Other factors include the severity of the paralysis (ie, partial or complete). Partial paresis is usually associated with a good prognosis for recovery as long as the underlying cause is addressed. The physician should also inquire about associated symp-toms. Those with severe otalgia and recent vesicular ear lesions sug-gest herpes zoster oticus. Ipsilateral facial numbness, altered taste, and decreased tearing occur frequently with Bell palsy. Hearing loss and ver-tigo may indicate tumors of the internal auditory canal or brain stem.

Recurrent episodes of facial palsy may be present with a tumor but also can occur with Bell palsy. Approximately 7% of Bell palsy patients may have recurrent facial paralysis. Other aspects of history include recent head trauma, otologic surgeries, and autoimmune disorders.

74

Pediatric Otolaryngology

■

■ Physical.Examination

A complete head and neck examination with emphasis on the ear is essential. External ear should be assessed for vesicular lesions. External ear canal and tympanic membrane may demonstrate evidence of otitis, cholesteatoma, or tumor. Children with history of trauma may show hemotympanum, perforation, or otorrhea. Clear fluid may be indica-tive of cerebrospinal fluid. Battle sign (mastoid ecchymosis) or raccoon eyes may occur with skull base fracture. A cheek or neck mass suggests a tumor, especially if facial paresis has been gradual in onset and seg-mental paresis is present.

A thorough neurologic examination should be performed. All branches of the facial nerve should be assessed and the 2 sides com-pared. The patient should be asked to maximally raise the brows, close the eyes tightly, wrinkle the nose, pucker, and smile widely. A unique challenge in the physical examination of newborns and very young children is that cooperation is limited and the clinician may need to observe for facial motion while the baby is crying or playing when spontaneous facial expressions occur. In addition, the young child has good facial muscular tone and may make the clinician underestimate the degree of paresis. Multiple cranial neuropathies suggest extensive trauma, infection, extensive neoplasm, or systemic neurologic disease.

The most common scale used and accepted to determine severity of facial paresis is the House-Brackmann classification (Table 3-1).

An important early distinction is to identify facial nerve deficit as a central or peripheral lesion. Central problems usually can be differenti-ated by a thorough neurologic examination because most brain lesions are not specific to be isolated only to the facial nerve. Because the upper face is innervated bilaterally from facial nerve tracts from the brain cor-tex, a cortical lesion results in facial paralysis of the lower face only.

■

■ Pathophysiology

Understanding the degree of injury is important in predicting facial nerve recovery. The Sunderland classification scheme is based on the histologic changes and physiologic implications (Table 3-2).

First-degree injury, or neurapraxia, occurs with increased intra-neural pressure such as a compression injury. Continuity of the axon is preserved, and the injury prevents conduction of an action potential.

No wallerian degeneration occurs. With relief of compression, complete recovery is expected.

Chapter 3: Facial Paralysis

Second-degree injury, or axonotmesis, occurs when trauma leads to obstruction of vascular flow and subsequent ischemia and breakdown of axons. If trauma is relieved, recovery requires axons to regenerate.

Duration of recovery, thus, is longer and may take weeks to months.

Endoneural tubes are intact and no crossover to other axons is expected.

Table.3-1...Facial Nerve Grading.System

Grade Description Characteristics

I Normal Normal facial function in all areas

II Mild dysfunction Gross: slight weakness noticeable on close inspection; may have very slight synkinesis At rest: normal symmetry and tone Motion

Forehead: moderate to good function Eye: complete closure with minimum effort Mouth: slight asymmetry

III Moderate dysfunction

Gross: obvious but not disfiguring difference between two sides; noticeable but not severe synkinesis, contracture, and/or hemifacial spasm At rest: normal symmetry and tone

Motion

Forehead: slight to moderate movement Eye: complete closure with effort Mouth: slightly weak with maximum effort IV Moderately severe

dysfunction

Gross: obvious weakness and/or disfiguring asymmetry

At rest: normal symmetry and tone Motion

Forehead: none Eye: incomplete closure

Mouth: asymmetry with maximum effort V Severe dysfunction Gross: only barely perceptible motion

At rest: asymmetry Motion

Forehead: none Eye: incomplete closure Mouth: slight movement

VI Total paralysis No movement

House JW, Brackmann DE. Facial nerve grading system. Otolaryngol Head Neck Surg.

1985;93(2):146–147. Reprinted by permission of SAGE Publications.

76

Pediatric Otolaryngology

Usually the typical pathologic processes that occur with Bell palsy or herpes zoster oticus are limited to first- or second-order injuries, and satisfactory recovery occurs in these individuals.

With third-degree injury, or neurotmesis, pressure is of enough severity or duration that endoneural sheaths are disrupted. Spontaneous recovery often is incomplete, and synkinesis is expected as regenerating axons may cross.

Fourth- or fifth-degree injury occurs when partial or complete transaction occurs, most often from external trauma. Fourth-degree injury occurs when partial disruption of the nerve occurs. In addition to disruption of the endoneurium, perineural disruption also occurs.

The only structure holding the nerve together is epineurium. Recovery potential is poor. Fifth-degree injury occurs when the nerve is com-pletely disrupted. No spontaneous recovery will occur.

DIAGNOSTIC TESTING

Because of the proximity of the seventh and eighth cranial nerves in the posterior fossa, pure tone and speech audiometry is recommended in all cases of facial paralysis. Radiographic imaging assists in delineating the site of lesion along the facial nerve. Computed tomography (CT) is best to assess temporal bone trauma, cholesteatoma, and otitis media.

Magnetic resonance imaging helps to assess when tumors or infections are suspected. First degree Neurapraxia Increased intraneural

pressure

Third degree Neurotmesis Loss of endoneural tubes Incomplete recovery, synkinesis

Disruption of entire nerve None

Adapted from Sunderland S. A classification of peripheral nerve injuries producing loss of function. Brain. 1951;74:491–516

Chapter 3: Facial Paralysis

When other, less common causes of facial paralysis are suspected, laboratory studies to evaluate for Lyme disease and autoimmune disor-ders should be considered.

Electrophysiologic tests are useful in establishing the prognosis of facial nerve recovery. Tests are complementary and are indicated when complete paralysis is present. They do not have a role in clinically evident partial paresis because recovery is expectant. Electromyography (EMG) records spontaneous, evoked, and voluntary electrical responses of motor end plates. In the acute setting, presence of voluntary active motor units indicates intact nerve with incomplete injury. In a dener-vated muscle, spontaneous involuntary contractions appear as fibrilla-tion potentials. These require 14 to 21 days to develop after facial nerve injury, thus limiting the role of EMG until this period when voluntary active potentials are absent. With recovery or regeneration, return of neural activity may be predicted by presence of polyphasic potentials, which may be present even though clinically evident facial motion is absent.

Other current clinically relevant tests to assess prognosis for return of function are nerve excitability test (NET), maximal stimulation test (MST), and electroneuronography (ENoG). These 3 tests may be performed 3 days after the onset of paralysis after wallerian degenera-tion has occurred. Even a completely transected nerve will conduct distally stimulated impulses for 48 to 72 hours. Thus, these tests have limited applicability during the first 3 days. Nerve excitability test is used to measure the current threshold for a barely perceivable facial motor response. The paralyzed side is compared with the unaffected side. Differences of greater than 3.5 mA are considered significant and indicative of nerve fiber degeneration and potential incomplete recovery. In MST, facial muscle contraction is elicited with the highest electrical current that the patient can tolerate. The response is expressed as the difference between the normal and paralyzed side and graded as minimal, moderate, severe, or no response.

Electroneuronography or evoked EMG is the recording of com-pound action potentials from the facial musculature in response to transcutaneous electrical stimulation of the facial nerve at the level of the stylomastoid foramen. Responses are compared from the 2 sides.

The percentage response compared with the unaffected side is propor-tional to the degree of degeneration. Surgical decompression is recom-mended in patients who have greater than 90% degeneration because of the high likelihood that recovery will be incomplete with medical management alone in these cases. The advantage of ENoG over NET or

78

Pediatric Otolaryngology

MST is that the response is quantitated and less dependent on the sub-jective observation of the tester in visualizing responses.

■