Congenital Facial Paralysis Workup

Updated: Jan 07, 2019
  • Author: Alan D Bruns, MD, FACS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Workup

Laboratory Studies

The workup for congenital facial paralysis does not involve any particular routine battery of lab tests. If the mother has a history of viral infection perinatally, viral titers (eg, herpes simplex virus) and a TORCH screen could be considered, but the probability of one of these infections causing a facial paralysis is low. If a neonate appears syndromic, then chromosomal analysis with technology such as florescent in situ hybridization (FISH) should be considered. In these infants with complete nerve facial palsy, an investigation for chromosome 22q11 deletions is recommended. [21] Molecular testing for CHD7 mutations may help to confirm the diagnosis and differentiate it from the 22q11.2 deletion syndrome. [35] Careful audiologic evaluation with an auditory brainstem response in these patients, and those patients with FSH MD, is advised so that a sensorineural hearing loss can be ruled out. [26]

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Imaging Studies

See the list below:

  • Conventional neuroimaging does not usually contribute to the understanding the pathogenic mechanisms of congenital unilateral facial nerve palsy except in the case of a very rare large pontine lesion, [36] mastoid tumor, [37] or internal auditory canal stenosis. [38] However, congenital bilateral facial nerve palsy is usually accompanied by other congenital disorders that can be identified. [39]

  • A CT scan of the temporal bone in both axial and coronal views may be considered in infants with complete paralyses from trauma that do not resolve and, thus, surgery is being considered. A temporal bone fracture or any bony spicules within the facial canal may be demonstrated. Associated anomalies of the external ear, middle ear, inner ear, mandible, and the vertical portion of the facial nerve would suggest a developmental etiology of the paralysis.

  • An MRI study provides better definition of the nerve and the surrounding soft tissue. Aplasia or hypoplasia of the nerve may be apparent; these findings strongly suggest a developmental anomaly. In addition, a hematoma or surrounding soft tissue swelling may be present when the paralysis is associated with trauma. This may be enhanced with a 3D-CISS MRI. [39]

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Other Tests

Electrophysiology tests of facial nerve function can be useful to determine the extent of nerve disruption and to assist with future surgical planning.

  • Electroneuronography (EnoG) is usually the study of choice.

    • This test involves a quantitative analysis of the extent of degeneration. It is not dependent upon the observer.

    • The summation potential is recorded.

    • If more than 90% degeneration has occurred in traumatic congenital facial paralysis consider surgical decompression. (In newborns, waiting 5 weeks is prudent.)

    • An EnoG within 48 hours of a congenital traumatic injury typically reveals normal facial nerve function, whereas, in congenital developmental paralysis, the initial EnoG reveals facial nerve function to be absent or weak because of longstanding neural degeneration or nerve absence. [10]

  • Nerve excitability test (NET)

    • This test compares current thresholds required to elicit minimal muscle contraction on the normal side with that of the weak side.

    • A difference of 3.5 µA is significant.

  • Maximal stimulation test (MST)

    • This test is similar to NET but uses maximal stimulation. It is valuable for determining the status of neuromuscular units.

    • If nerve conduction is neurapraxic, response is positive; if nerve conduction is degenerated, response is absent.

    • Sectioned nerve can still be stimulated for 24-72 hours after injury; thus, the test cannot be interpreted until 3 days later.

    • The test is graded subjectively (equal, decreased, absent).

  • Electromyography (EMG)

    • This test determines the amount of activity of muscle itself. It records motor unit potentials of voluntary and involuntary muscle contraction, as well as spontaneous muscle fiber activity.

    • Degeneration of lower motor neuron is followed by fibrillation potentials at 14-21 days.

    • Polyphasic potentials can be observed 6-12 weeks before clinical improvement.

  • Topodiagnostic studies: Not performed routinely in the workup for congenital facial paralysis.

    • Schirmer test: This test evaluates function of the greater superficial petrosal nerve (lacrimation). A reduction of more than 30% or less than 25 mm in 5 minutes is significant.

    • Stapedial reflex: If the lesion involves the nerve proximal to the branch to the stapedius muscle, the stapedius muscle does not contract and no change in impedance is evident when testing the acoustic reflex.

    • Salivary flow: Wharton papillae are cannulated, and salivary flow is measured in response to a gustatory stimulus. An abnormal result is a reduction of 25% in salivary flow compared with the noninvolved side.

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