EMG knowledge Flashcards
Filter settings Sensory NCS
20Hz to 10 kHz
also listed as 20-2000Hz
Filter setting for Motor NCS
2Hz to 10kHz
Filter settings for EMG
20Hz to 10kHz
Sensory sweep speed ( X-axis)
5 msec
Sensory sensitivity (gain), Y-axis
10uV-20uV
Sweep speed motor
2msec
Sensitivity motor
5mV
EMG sweep speed
10 msec
EMG sensitivity
100uV for insertional activity
1mV for recruitment pattern analysis
Normal temp for upper limb
32 degrees
Normal temp for lower limb
30 degrees
What happens to these parameters when electrodes are less than 4cm apart Peak latency: ? Amplitude: ? Duration: ? Rise time: ?
Peak latency: Decreased
Amplitude: decreased
Duration: Decreased
Rise time decreased
For SNAP:
Anatomy examined
Pertinent latencies
Amplitude measurements
Anatomy examined: sensory nerves
Pertinent latencies: Peak or onset
Amplitude measurements: peak to peak (uV)
For CMAP:
Anatomy examined
Pertinent latencies
Amplitude measurements
Anatomy examined: Motor nerve fibers, NMJ, muscle fibers
Pertinent latencies: onset latency
Amplitude measurements: Baseline to peak mV
H reflex formula
9.14 + .46 (leg length in centimeter from the medial malleolus to the popliteal fossa) + 0.1 (age)
H reflex normal value
side to side
28 to 30msec
Side to side difference 1.5 msec is significant
> 60 years: adds 1.8 msec
temp not an important factor as H-reflex the pickup is over a more proximal (and therefore warmer) muscle.
F wave:
Normal
Side to side difference
Normal:
Upper limb: 28 msec
Lower limb: 56 msec
Side to Side difference:
2 msecs in upper limb is significant
4 msec in the lower limb is significant
decreased persistence (occurrence) on repetitive stimulation correlates with a potential abnormality
Median motor
Amp >5
DL <4.2
Sural
Amp >5
DL <4.2
Median sensory
Amp > 15
DL <3.7
Ulnar motor
AMP> 4.6
DL <4
ulnar sensory
AMP> 12
DL <3.6
Combined sensory index
CSI: ringdiff+ thumbdiff+ palmdiff
CSI peak distal latencies > 1ms is abnormal
> 5ms difference from peak latencies is abnormal in each
Dorsal Ulnar cutaneous (bar)
Amp> 5
DL <2.9
Radial motor
Amp>2
DL <2.9
Amp>4.5
DL < 2.1
Radial sensory
Amp >15
DL <2.9
AMP>7
DL <2.8
MAC
AMP>4
DL <2.6
LAC
AMP >5
DL <2.5
peroneal motor
AMP>2
DL <6
Tibial motor (medial plantar nerve)-AHB
AMP>4
DL <6
Tibial motor (lateral plantar branch)-FDMB
Amp >6.1
DL <8.3
femoral motor
AMP> 3
DL <7.4
superficial peroneal sensory
AMP >15.1
DL <4.2
Muscles innervated by PIN
- Supinator
- Extensor Carpi Radialis Brevis
- Extensor digitorum communis
- Extensor digiti minini
- Extensor carpi ulnaris
- aBductor pollicis
- extensor pollicis brevis
- Extensor pollciis longis
- extensor indicies
Sites of compression of PIN
- Arcade of Froshe
- supinator muscle
- extensor carpi radialis brevis muscle
- Leash of henry (recurrent radial vessels that fan out across the PIN at the level of the radial neck)
- Fibrous tissue anterior to the radiocapitellar joint
Diabetic Amyoptrophy
Also known as: proximal diabetic neuropathy, diabetic lumbosacral radiculoplexus neuropathy, and diabetic polyradiculopathy.
occurs in patients with diabetes (Type II>Type 1), Usually involves weakness followed by wasting of muscles, and excruciating pain in the muscles of thigh, hip, and buttocks. Symptoms sudden in onset. The weakness involves the thigh and the leg so patients have difficulty getting out of chairs and often require cane or crutches.
ALS symptoms classically do not include
loss of extraoccular control, bowel/bladder dysfunction, or dementia
ALS most likely inherritance pattern
ALS runs in families, most likel autosomal dominant
A family history in a second- or third-degree relative or a family history of frontotemporal dementia should also be regarded as strong evidence in support of a diagnosis of?
Familial ALS
What needle type is best for isolated MUPs
bipolar needle
The onset latency
represents the conduction speed of the fastest fibers
EMG myopathy findings
low amplitude, short duration, polyphasic motor units with early recruitment.
On needle electromyography (EMG), normal motor units have a duration of:
5-15msec
Duration is the time from the initial baseline departure to the final return to baseline. Normal duration is about 5 to 15 msec or approximately one horizontal division with a commonly used sweep speed of 10 msec/division. It represents the degree of synchrony in the firing of the individual motor fibers that contribute to the motor unit. With reinnervation, there is asynchrony of firing of individual muscle fibers due to immature myelin. Therefore, duration of a motor unit increases with reinnervation and can be seen in chronic neuropathic processes. Decreased duration may be seen in myopathic disorders.
In the newborn, nerve conduction velocities are approximately what percentage of adult values?
At birth, most of the myelination is incomplete. Conduction velocities are about 50% of adult values. By 1 year of age, the velocity is about 75%. Myelination is usually complete by age 3 to 5 years.
Rich Canau anastomosis
anastmosis between deep ulnar branch and reccurent medial nerve
CRDS
CRDs are usually noted in longstanding disorders (of more than 6 months). They represent groups of spontaneously firing action potentials with an affected area of muscle electrically stimulating an adjacent muscle fiber. This produces a local muscular arrhythmia. The patterns repeat regularly with a frequency of 10 to 100 Hz. They have the sound of a motorboat misfiring. They can be seen in chronic neurogenic or myopathic disorders. As the needle study would be normal in a sensory neuropathy (only the motor fibers are tested with needle testing), CRDs would not be noted in a sensory peripheral neuropathy.
EMG findings in spinal stenosis
In spinal stenosis, there is narrowing of the vertebral canal, which is usually exacerbated by extending the spine (standing) and relieved with flexion of the spine (sitting). Pain may radiate from the back down to the extremities, especially with extension of the spine. SNAPs are normal as the dorsal root ganglion (DRG) is located outside the spinal canal. CMAPs should not be affected as the distal portion of the nerve is not affected. There may be abnormal spontaneous potentials at rest (positive sharp waves [PSW] or fibrillations) or chronic motor unit action potential (MUAP) changes (polyphasic potentials) that are often bilateral. Bilateral paraspinals and extremities should be tested for EMG abnormalities.
Denervation can be found
in neuropathic or myopathic processes.
Alcoholic neuropathy
sensory & motor axonal neuropathy
Paraneoplastic syndrome***
sensory axonal neuropathy
Guillain-Barré syndrome
segmental demyelination
Diabetic neuropathy
sensory and motor, axonal and demyelinating peripheral polyneuropathy.
flexor pollicis brevis
the median and ulnar nerves
Normal amplitude for a MUAP
Normal amplitude of a motor unit using a monopolar needle is about 1 to 7 mV in amplitude.
adductor magnus is innervated by
This muscle has dual innervation from both the Obturator nerve and the Tibial division of the Sciatic nerve.
A-waves
seen in chronically injured nerves and represent regeneration or collateral sprouting of a nerve, as the orthodromic response is diverted along a collateral neural branch to circumvent the conventional path. This alternative path has a constant latency and is seen between the M- and the F-wave, with Submaximal stimulation.
CSI
Thumb diff, ring diff, palm diff. f the added differences total more than 0.9 msec, CTS is confirmed.
SSEPs
may be helpful in diagnosing problems in sensory nerves (such as in meralgia paresthetica, also known as lateral femoral cutaneous nerve injury) that are not accessible to routine electrodiagnostic testing. SSEPs are not the test of choice in assessing for a radiculopathy, as only the sensory pathway is tested and the pathway is very long. Problems anywhere along the pathway may affect latency and amplitude. They are not at all useful in assessing motor nerves (anterior interosseous nerve injury). The pathway is too long to be of use in a sacral plexopathy.
somatosensory-evoked potentials can also assess autonomic nerves
Hereditary neuropathies
uniform-demyelinating neuropathies. They will therefore show uniformly slowed conduction velocity without temporal dispersion. Temporal dispersion would be seen in segmental demyelination, where some fibers are conducting much slower than others.
Critical illness neuropathy
sensorimotor axonal neuropathy.
Latencies and conduction velocities remain normal to borderline normal. Should test at least 3 limbs.
(If the fastest axons are affected, latency may be mildly increased, and conduction velocities mildly decreased. However, the axonal loss (amplitude) is out of proportion to the slowing.)
Acquired neuropathies
are usually more distal or segmental then hereditary neuropathies. Temporal dispersion is a feature of an acquired neuropathy.
paraneoplastic syndrome.
A patient who has low-amplitude sensory nerve action potentials with preserved compound motor action potential amplitudes (and relatively normal conduction velocities and latencies) should be suspected of having a paraneoplastic syndrome.
What errors would decrease NCS amplitude
not stimulating over the nerving
not giving enough stimlation
What error would result in the latencies being delayed
reversing the anode and cathode
If the anode and cathode were reversed on the stimulator, there would be an extra 3 to 4 cm in length between the stimulator and the active electrode.
SDSA
In myopathies, motor units usually have low amplitude (less than 1 mV when using a monopolar needle), short duration, polyphasicity, and early recruitment.
The X-axis (sweep) represents
time, which is usually in milliseconds per division.
During repetitive nerve stimulation in a patient with myasthenia gravis, what should be seen?
In repetitive nerve stimulation, a greater than 10% decrease in CMAP amplitude from the first to the fifth stimulation is considered significant for pathology at the neuromuscular junction.
To assess whether a patient has a peripheral neuropathy, it is necessary to?
test sensory AND motor nerves in three limbs
The rise time is measured as
time from the peak of the initial positive deflection to the subsequent negative upward peak
H-reflex elicited in any muscle besides the gastrocnemius-soleus or the flexor carpi radialis is considered…
pathological and may indicate an upper motor neuron lesion.
when the gain is set at 100 mcV/division you can better assess
fibs, positive sharp wave (PSW), or an end-plate potential
