LEMG: Understanding the Results
What do the LEMG results mean?
Overview
LEMG
can give specific information on whether nerve function to the voice
box muscle being studied is intact (normal), partially intact (as in
paresis), or absent (as in paralysis).
- LEMG results, together with the results of
other tests and clinical examinations, will be used to determine
whether nerve inputs to muscles involved in voice, breathing, or
swallowing disorders are present or absent, and (if present) normal or
abnormal.
- The results may also indicate that more medical tests are necessary before a diagnosis and treatment plan can be developed.
LEMG is analyzed according to five parameters:
- Insertional activity
- Spontaneous activity
- Recruitment
- Waveform morphology
- Synkinesis
Five-Point Analysis on LEMG
| Parameter |
Definition |
Information |
1. Insertional activity |
Electrical discharges when needle is inserted into the muscle |
Normal: Bursts of discharge last only less than several hundred milliseconds
Abnormal: Bursts are longer or shorter than normal |
2. Spontaneous activity |
Electrical discharges recorded while a muscle is at rest (no talking, no swallowing) |
Normal: No electrical activity in muscle at rest (except when close to a connection between nerve and muscle in study)
Abnormal: If present, indicates abnormality (except when resting muscle is NOT completely relaxed) |
3. Waveform morphology (on voluntary activity) |
Size, shape, timing pattern of electrical activity during voice tasks |
Normal: Specific size, shape, timing, and duration of electrical activity
Abnormal: Decreased size; waveform shape complex or polyphasic; timing; altered duration of electrical signals |
4. Recruitment (during voluntary activity) |
Increase of electrical activity as patient increases force of muscle contraction |
Normal:
Increased effort of muscle contraction results in inclusion
(recruitment) of other motor units, hence increased electrical
activity, until all electrical signals blend
Abnormal: Abnormal or decreased recruitment patterns |
5. Synkinesis ("crossed wires") |
Electrical activity is recorded in a muscle that is not active during a particular task |
Abnormal: Presence of synkinesis NOT a normal finding
- "crossed wires": wrong muscle moves at the wrong time
- may develop when nerves regenerate in an abnormal way
|
Other abnormal patterns
Examination
of other abnormal patterns of muscle activity during voluntary
contraction is also performed. For example, detection of regular,
rhythmic bursts of electrical activity during a sustained contraction
may indicate a tremor.
These findings, taken together, can
help pinpoint the cause of the voice disorder, indicate the need for
further testing, and/or suggest a certain treatment strategy.
For example, the table below shows what LEMG results would most likely indicate in a patient with a non-moving vocal fold:
| Spontaneous Activity |
Recruitment |
Waveform Shape |
Interpretation in Patient With Voice Disorder With Non-moving Vocal Fold |
Absent |
Normal |
Normal size, shape, pattern |
Normal nerve input to voice box muscle tested:
Cause of vocal fold immobility not due to paralysis of said muscle |
Absent |
Reduced |
"Nascent": small size, long duration, complex shapes |
Reinnervation present:
Recovery is ongoing and likely; "hold" on intervention |
Absent |
Reduced |
"Giant": large size, long duration |
Old injury:
Spontaneous further recovery unlikely; decide on intervention |
Present |
Absent |
Fibrillations, positive waves, complex repetitive discharges |
Denervation ongoing: Medical
consultation is necessary to determine cause of denervation |
|
