Table 2.
Proposal for a routine examination for facial electrodiagnostics
| Step | Test | Comment |
|---|---|---|
| 1. | Prearrangements | Constant conditions are important to reduce re-test variability. Constant room temperature, optimal electrical shielding, regular control of equipment. Abrasive cleaning of the skin areas where the electrodes are to be placed and alcohol cleaning is needed where the stimulator is placed. An adjustable chair/examination couch for the patient is recommended |
| 2. | Electroneurography (ENoG) |
Setting example: Sensitivity 10,000 mV; amplifier filtering 1–10 kHz; time frame 10 ms; stimulus duration 200 µs; Maximal stimulus limited to 20 mA; Stimulus rate 1.9 s; Data recorded and averaged using a stimulus rate of 1 Hz with sensitivity adjusted to 2 µV/division and filters set at 30 Hz to 3 kHz a) Ground electrode: Arm or neck; b) Stimulation first on the healthy, then on the paralyzed side; c) Recording electrodes: nasal alae next to each other; d) Stimulator placed on stylomastoid groove; e) Stimulation starts with 0.1 mA and is increased until the maximal CMAP occurs. Stimulation is then once more slightly increased (supramaximal stimulation); f) Storing of the CMAP and measurement of the other side g) Ratio of the peak-to-peak amplitude of the paralyzed side in relation to healthy in percent is calculated |
| 3. | Needle EMG (nEMG) |
nEMG of frontalis, orbicularis oculi, oris and zygomaticus muscle on the affected side gives an overview of the facial nerve function. Of course, the selection depends on the facial nerve lesion and the diagnostic questions. The sequence of evaluation is always the same for each muscle: 1. Insertion activity 2. Spontaneous activity at rest 3. Activity during voluntary muscle movement 4. In case of chronic palsy: Synkinetic activity 1. The needle electrode is softly inserted in an oblique angle into the first facial muscle of interest. Normally, the needle is moved during the evaluation to see and hear the optimal placement and recording The muscle activity is graded as follows: a) No activity b) Normal activity (< 300 ms) c) Increased activity d) Highly increased activity 2. The patient is instructed to relax the muscle. The observer should wait a while until the spontaneous activity occurs. Spontaneous activity should be recorded and classified as: a) No reproducible pathologic spontaneous activity b) Little pathologic spontaneous activity c) Moderate pathologic spontaneous activity d) Dense pathologic spontaneous activity 3 The patient is instructed to perform a standard talk for the specific muscle (For instance, frowning for the frontalis muscle, closing the eye for the orbicularis oculi muscle, showing the teeth for the zygomatic muscle). The maximal possible activation of the muscle is documented as follows: a. No activity b. Single fiber pattern c. Severe decreased recruitment pattern d. Mildly decreased recruitment pattern e. Normal/dense recruitment pattern The waveform of the MUAPs is also classified as: a. Normal biphasic motor unit potential b. Early (sometimes polyphasic) reinnervation potentials with low amplitude and long duration c. Giant polyphasic reinnervation potentials with high amplitude and long duration d. Myogenic polyphasic potentials with low amplitude but in many cases normal duration 4. If the patient should be examined for synkinetic activity, step 3 is repeated but the task for another muscle is used, for instance closing the eye while recording from the orbicularis oris muscle. Alternatively, and more precise is to record synchronously an nEMG from different muscles and varying the tasks. Synkinesis is documented as follows: f. Investigated muscles g. Used task h. Few/moderate/strong/very strong synkinesis |
| Additional test for selected cases | ||
| 4. | Blink reflex |
Baseline setting like for ENoG or nEMG. Band pass of 20–1000 Hz, pulse duration of 100 µs, repetition rate of 1 Hz, sensitivity of 500 µV/division, and sweep speed of 5 ms/division a) Ground electrode: arm or neck; b) Stimulation normally only the paralyzed side; c) Recording surface electrodes: lateral part of orbicularis oculi muscle on both sides; d) Stimulator placed on supraorbital nerve; e) Stimulation starts with 0.1 mA and is increased until the maximal CMAP occurs. Stimulation is slightly increased (supramaximal stimulation); f) Storing of the CMAP and measurement of the ipsilateral R1 component and of the bilateral R2 component; measurement of the latency of R1 and R2 and of the side difference of the latency of R2. Documentation of the absolute values and interpretation of the results: 1. R1 latency normal (≤ 12 ms) or prolonged (> 12 ms) 2. R2 latency normal (≤ 40 ms) or prolonged (> 40 ms) 3. R2 latency side difference normal (≤ 5 ms) or larger (> 5 ms) |
| 5. | Surface EMG (sEMG) |
Baseline setting like for ENoG or nEMG a) Ground electrode: arm or neck; b) Selection of facial muscles and placement of the surface electrodes depends much on the question of the observer; c) Typically, bilateral recordings are performed, but for analysis of synkinetic activity, also unilateral recording may be the best option d) sEMG is recorded while subjects perform facial movements for test purposes, including: pressing the lips together, pulling the corners of the mouth downwards, smiling—pulling the corners of the mouth upwards and backwards, depressing the lower lip, protruding the lower lip, pulling the upper lip upwards, pulling the upper lip upwards and depressing the lower lip simultaneously, pursing lips, blowing out the cheeks, whistling with a similar tone pitch, exhaling forcefully with moderate closed lips (a more diffuse whistling), opening the lips as wide as possible while the jaw is closed, wrinkling the nose, raising the eyebrows up and wrinkling the forehead, contracting the eyebrows, closing the eyelids forcefully, squinting the eyes, closing the right eyelid, closing the left eyelid e) For documentation are important: 1. Analyzed muscles 2. Analyzed tasks 3. Observation of maximal sEMG activity 4. Sequence of recruitment if several facial muscles are involved in the specific task 5. Observation of synchronous and asynchronous activity |
| 6 | Transcranial magnetic stimulation (TMS) |
Basis setting like for ENoG or nEMG a) Ground electrode: arm or neck; b) Stimulation first on the healthy, then on the paralyzed side; c) Recording electrodes: nasal alae next to each other; d) Magnetic stimulator placed on ipsilateral parieto-occiptal region (in special cases on contralateral motor cortex); e) Typically, a magnetic field of up to 2 T (with short duration of only 2–3 ms) is generated. The intensity is indicated on the TMS machine in percentage of the maximal magnetic field output Stimulation starts with 5% and is increased until the maximal CMAP occurs. Stimulation is slightly increased (supramaximal stimulation); Normally, about 30–40% of the maximal output are sufficient to obtain supramaximal response; f) Storing of the CMAP and measurement of the other side g) Ratio of the peak-to-peak amplitude of the paralyzed side in relation to healthy in percent is calculated |
| 7 | Facial nerve mapping (FNM) |
FNM is not part of classical facial electrodiagnostics. FNM might be helpful as anpreoperative tool to foresee the course of the peripheral facial nerve and its main branches in the individual patients Baseline setting like for ENoG or nEMG a) Ground electrode: arm or neck; b) Transcutaneous stimulation normally only the paralyzed side; c) Stimulation with monopolar electrode (for instance, all ball electrode, 8 mm); d) Electrostimulation with monophasic, rectangular single pulses with duration of 250 µs. The stimulation at each stimulation point started with 0.1 mA; increase in 0.1 mA steps. Increase of the stimulation intensity is stopped when a muscle contraction is seen; e) Stimulation site is marked with a muscular response is seen at the stimulation place; f) When stimulation at one point is finished, stimulation electrode is moved forward, stimulation procedure is repeated g) Finally, each point triggering a motor response is marked on the skin |