Electroneuronography (ENOG) Flashcards
(44 cards)
What is ENOG?
Neurological non-invasive test used to study the facial nerve in cases of muscle weakness in one side of the face or with Bell’s palsy
First used by Esslen and Fisch in 1979
The termnerve conduction studyis employed for other nerves
Terminology for the facial nerve itself
Electroneuronography is used as a marker to determine course of action in managing disease or to monitor status
Based upon ENOG response, the physician may opt for continued observation or they may recommend surgery to address the damage
What does ENOG consist of?
Brief electrical stimulation of the nerve at one point underneath the skin and at the same time recording the electrical activity (compound action potential) at another point of the nerve trajectory in the body
The stimulation and recording are measured by disc electrodes taped to or disposable electrodes
Is conducting gel used to bolster signals?
Yes
Input and output
Can recording electrodes also pick up the electrical activity of the muscle innervated by the facial nerve?
Yes
In such instances electroneuronography is closely related toelectromyography (EMG)
Is ENOG typically concerned with the amount of degradation of facial nerve function?
Yes
What are facial nerve disorder etiologies?
Bell’s Palsy (most common)
Iatrogenic (surgical injury)
Trauma to the temporal bone
Otitis media (what starts in the ME can invade the IE)
Herpes Zoster Oticus
Multiple Sclerosis
Melkersson-Rosenthal Syndrome
Mumps
Chicken pox
Guillan Bare Syndrome
CVA (stroke)
Glomus Jugulare
Meningioma
Facial Nerve neuroma
Mastoiditis
Idiopathic
Other
Is the incidence for Bell’s Palsy or facial weakness?
70/100,000 cases
127,000 cases annually
Rare
How many fibers does the facial nerve have?
Approx 10,000 (2/3 motor and 1/3 sensory)
Been proposed that only half of the motor units need to be functional for normal nerve conduction to take place
Where does the facial nerve run?
The facial nerves originate in the brainstem, crosses through the auditory canal, exits the skull at the stylomastoid foramen and terminates on each side of face where they control muscle contractions and facial expression
Does innervation get more complex as it gets further out?
Yes
What are indications of a lower motor lesion?
Asymmetry to face
Eyebrow droop
Mouth droop
Tearing of eye
Inability to close eye
Inability to purse lips
Inability to smile/frown
Nostril control
What are indications of an upper motor lesion?
Facial asymmetry
Atrophy muscles lower face affected side
No eyebrow droop
Can still close eye
Inability to purse lips
Inability to smile/frown
Nostril control
What is denervation?
Any loss of nerve supply regardless of the cause
If the nerves lost todenervationare part of the neuronal communication to a specific function in the body then altered or a loss of physiological functioning can occur
Used to denote any loss of nerve supply or activity
Nerves don’t immediately stop working after injury
Part away from the cell body will remain active for a little after the injury (crushed or cut)
What is wallerian degeneration?
An active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. farther from the neuron’s cell body) degenerates
Begins 24-36 hours after injury
Complete denervation takes place 72 hours
Axon is still active prior to this
Need to wait a few days after the trauma to understand the true capability of the nerve - but not too long because intervention might not be possible
What is the sweet spot to perform ENOG after injury?
3 days to 21 days after onset of symptoms
What are the measures to classify nerve injury?
Sunderland and Seddon Injury Classification
House-Brackmann Facial Nerve Grading
*worse grades would be sent on for ENOG testing
What three broad categories did Seddon classify facial nerve injuries into?
Neuropraxia
Neurotmesis
Axonotmesis
What is neuropraxia? (Seddon)
Most common form of injury associated with Bell’s palsy, and it is characterized by paralysis without a degeneration of the peripheral nerve
ENOG would yield a normal or mildly impaired response, as the nerve fibers are still whole but unresponsive to conscious control
What is neurotmesis? (Seddon)
The worst possible outcome, with ENOG readings equivalent to a flat line, or no response to stimulation
This represents total degradation of the facial nerve
What is axonotmesis? (Seddon)
Damage to the inner nerve fibers while the outer covering remains whole, and also yields a flat line in response to stimulation
Because of their similar recordings, ENOG cannot, by itself, distinguish between the latter two forms of nerve injury
What is the House-Brackmann Scale?
The standard used by medical professionals to evaluate facial nerve function
It is a measure of the range of intentional motion the patient’s facial muscles have, and is based largely on the observations of the physician
Because of the subjective nature of the scale, there may be discrepancies between assessments by different doctors, but the overall reliability and ease of use has made this scale the most commonly employed by medical professionals
The scale itself consists of six levels of facial nerve function, ranging from healthy (level 1) to a total lack of movement (level 6)
What do the grades of House-Brackmann mean?
The level at which the patient’s facial nerves are functioning is reported as a fraction of the 6 levels
Therefore, someone with normal facial nerve integrity would be reported as “1/6,” or “level 1 of 6”
Grade two is associated with mild weakening of the facial nerve, and grades three and four have moderate damage, varying only on the basis of the ability to close the eye
The next two levels include severe impairment and total paralysis, respectively
Electroneuronography may only be employed in the most severe instances (5/6 or 6/6) because in the other cases there is clear evidence that the nerve is mostly intact
What does grade 2 look like?
Slight weakness with effort, may have mild synkinesis
Normal resting appearance
Mild oral and forehead asymmetry
complete eye closure with minimal effort
What does grade 3 look like?
Obvious asymmetry with movement, noticeable synkinesis
Normal resting appearance
Mild oral asymmetry, complete eye closure with effort, slight forehead movement
