Electrodiagnosis Flashcards
Results Aid in The Diagnosis of Peripheral Nervous System Disease; Goal of Test - To observe the time and quality of the conduction of a nerve impulse in motor & sensory axons
Nerve conduction test
The impulse of a nerve impulse is analyzed for what conduction features?
- Amplitude
- Duration
- Shape of the waveform
- Conduction velocity
- Latency (time for nerve impulse transmission)
Velocity becomes slower in conditions with a decreased ______. What does decreased velocity indicate?
amount of myelin
- results indicate demyelination or entrapment
Decreases in the amplitude of the impulse with normal or slightly slowed velocity indicate ___________.
axonal degeneration
The first response in a NCT; Proximal Stimulus travels distally (Orthodromic) to the muscle results in the
M wave response
- determines peripheral entrapment
- early response
- measured in the muscle
In a NCT; Impulse also travels proximally (Antidromic) to anterior horn cell reactivating the motor neuron, impulse travels distally resulting in the
F wave response
- determines more proximal entrapment (i.e., ventral root)
- measured in the muscle
____ used to evaluate nerve segments peripheral to the point of stimulation. _____ used to evaluate more proximal motor nerve segments to the point of stimulation.
M Wave; F Wave
During an NCT, what wave is used to assess disorders like guillan-barre, charcot-marie-tooth, and thoracic outlet?
F wave
Proximal stimulus – impulses travel distally and are recorded from a branch of the sensory n.
- Disadvantage: motor and sensory n. stimulated resulting muscle contraction and movement artifact that could introduce measurement error.
Antidromic sensory NCT
Distal stimulus – impulses travel proximally, a more specific measure of sensory n. conduction.
Orthodromic sensory NCT
What is the clinical use of evaluating the H reflex?
Most useful to evaluate proximal conduction of IA afferent impulses through the dorsal root to the alpha motor neurons, which pass out of the S1 foramen to innervate the soleus muscle
Represents conduction along trigeminal N. and facial N. measured in orbicularis occuli muscle; never recorded from contralateral Obicularis oculi muscle
First response (R1)
Represents the time of conduction along the trigeminal pontine relay and facial nerve (Ipsilateral recording)
Second response (R2)
Contralateral recording opposite side of stimulus
Second response (R2') - stimulus crossed over through the pons
What is the clinical use of the blink reflex?
- brain stem pathologies
- Bell’s Palsy and other facial N. injuries
- trigeminal neuralgia
- multiple sclerosis
- Guillain – Barre’ syndrome
- Charcot-Marie-Tooth disease
- Whiplash injuries with dizziness
What disease is indicated with a blink reflex measurement: Amplitude of R2 is decreased;R2 may be delayed
Bell’s palsy
What disease is indicated with a blink reflex measurement: R2 for ipsilateral stimulation of right side would be prolonged. R2’ for contralateral stimulation on both sides would be delayed due to impaired transmission through the tumor site. Left R1 and R2 for ipsilateral stimulation would be normal.
Right brain stem tumor
What test would you use results to evaluate the NMJ for the presence of diseases?
repetitive stimulation tests
- bronchogenic carcinoma – presynaptic
- botulism toxin – presynaptic
- myasthenia gravis - postsynaptic
Supramaximal Stimuli at 3-5/sec delivered to a peripheral nerve at a distal site and changes in the amplitude of the electrical muscle response is evaluated: M – Wave Amplitude is evaluated
repetitive stimulation tests
What is considered abnormal in a repetitive stimulation tests?
- Amplitude decrease more than 10% in the 5th or 6th muscle response; consistent with myasthenia gravis (postsynaptic)
- Amplitude increases; consistent with bronchogenic carcinoma and botulism (presynaptic)
What are the three major types of clinical evoked potentials?
- Somatosensory evoked potentials
- brainstem auditory evoked potentials
- visual evoked potentials
Measurement: Orthodromic sensory impulses (e-stim evoked) travel through dorsal root ganglia, into spinal cord, and synapse with CNS dendrites, then projected to contralateral sensory cortex. Surface Recording Electrodes are placed on the contralateral Scalp
Somatosensory evoked potentials (SSEP)
- Clinical Use: patients with spinal cord injury, useful when other tests are not conclusive
Measurement: Through headphones, a series (1000-2000) of high-amplitude clicks are applied to the auditory receptors of the ears. Surface recording electrodes are placed (ipsilateral) on the top of the head
Brainstem auditory evoked potentials (BAEPs)
- Clinical Use: Patients with hearing loss with suspected acoustic neuromas, demyelinating diseases, multiple sclerosis. Also, used as initial screening test
Measurement: Focused synchronous volley (100-200) of visual stimuli (flashing lights etc.) are applied to the eye(s). This produces afferent impulses in the optic N. Surface recording electrodes are placed over occipital scalp area
Visual evoked potentials (VEPs)
- Clinical Use: Determining early demyelinating disease, especially the early stage of multiple sclerosis. VEPs latency is prolonged with demyelination of the optic n.
clinically useful in evaluating the electrical activity of lower motor neurons and muscle fibers in the presence of pathology
clinical electromyography
- The final EMG interpretation is correlated with other diagnostic test information and clinical findings and used in formulating a diagnosis and/or determining a plan of treatment
How is the typical EMG evaluation done in a skeletal muscle?
- Needle Electrode Insertion
- EMG Recording while muscle is at rest
- EMG Recording during minimal muscle contraction.
- EMG Recording during a muscle contraction graded from weak to strong or maximum
- responses to all 4 steps are evaluated
What is a normal and abnormal response during EMG needle insertion?
- Normal Response: Increased frequency of potentials during needle movement that lasts for a few milliseconds
- Abnormal Response: The increased frequency of potentials during needle movement lasts for a longer time, may be consistent with injury to neural supply of the muscle.
What is a normal and abnormal response in EMG recording during rest?
- Normal Response: The muscle is electrically silent, except for the normal brief bursts of electrical activity during needle insertion.
- Abnormal Response: Spontaneous Activity, Fibrillations, positive sharp waves, fasciculation potentials are observed especially with lesions of peripheral nerves
What is a normal and abnormal response in EMG recording during low force muscle contractions?
- Normal Response: The resulting potentials should be two or three phases. Amplitude and durations of potentials consistent.
- Abnormal Response: More than 10% of the resulting potentials are polyphasic. Amplitudes and durations of potentials may be increased or decreased, or may be absent.
What is a normal and abnormal response in EMG recording during maximal force muscle contractions?
- Normal Response: As the contraction is graded from low to high force, larger motor units are recruited resulting in potentials of greater amplitudes, with all motor units firing at increased frequencies such that individual action potentials cannot be discerned resulting in a full or complete interference pattern.
- Abnormal Response: Incomplete interference with maximal contraction, i.e., individual potentials can be observed, e.g., in peripheral neuropathies.
Asynchronous discharge of denervated muscle fibers; Seen in neuropathies and myopathies
Positive Sharp Wave Potentials
Results from asynchronous discharge of muscle fibers in the motor unit; Seen in compressive neuropathies & muscular dystrophy, and in Motor units undergoing reorganization
Polyphasic potentials
- motor unit potentials not firing all at the same time like they should be
- seeing early phases of remyelination
What EMG changes are seen with ALS, polio, and cervical spondylitis?
- Increased Amplitude and Duration of MUPs*
- Increased polyphasic potentials*
- Spontaneous activity in resting muscle
- On strong contraction, see partial interference pattern (ed number of rapidly firing large MUPs are recruited)
* may be related to increased axonal sprouting to orphaned muscle fibers, i.e. reorganizing of motor units
What EMG changes are seen with motor nerve compromise?
- Spontaneous Activity in Resting Muscle
- Increased Polyphasic Potentials
- Decreased recruitment of MUPs during strong contraction results in incomplete interference pattern.
- As lesion improves these changes reverse and become more like a normal EMG.
- No EMG Changes if only sensory roots are injured.
What EMG changes are seen with motor nerve regeneration?
- The presence of even a few MUPs suggests a more optimistic prognosis.
- Low amplitude polyphasic MUPs gradually appear overtime with regenerating axons.
- Spontaneous activity decreases with regeneration, but can be present for several years
What EMG changes are seen with demyelinating disorders and diabetic neuropathy?
- spontaneous EMG activity
- No major EMG changes with Guillain-Barre unless there is axonal damage
What EMG changes are seen with myopathic disorders?
- In advanced stages, severe muscle atrophied muscle produce short duration, low-amplitude potentials.
- Spontaneous potentials, fibrillations, prolonged increased frequency of needle insertion EMG potentials, and positive sharp waves are more frequent in inflammatory disorders
How is a NCT performed for motor and sensory testing?
- essentially same for both, just in opposite directions (orthodromic=motor, antidromic=sensory)
- Monophasic pulsed electrical stimulus is applied to the skin overlying the n.
- Evoked AP Travels in both Directions
What are the indications for NCT of motor neuron
- rule out peripheral neuropathy
- Determining and localizing peripheral entrapment or plexopathy; e.g., peripheral entrapment of the median n. at the wrist vs. a more proximal lesion of the lateral cord of the brachial plexus or cervical radiculopathy
What are the characteristics of the F wave for clinical use?
- Several supramaximal electrical Stimuli, because the F wave is inconsistent in occurrence.
- Is inconsistent in wave form usually < 500 µV in amplitude (F waves are in microvolts, M waves are in millivolts)
- Latency value for F waves falls within range of normal values.
- Most clinical assessments report only the F wave latency in msec
What considerations should you take when conducting motor and sensory nerve tests in children and older adults?
- Motor and Sensory N. Conduction slower in infants, approaching low-normal adult values at age 3
- Slowing of sensory conduction can occur in normal humans over age 65 years
uses both the afferent (sensory) and efferent (motor) peripheral N’s; consists of electrical stimulus of IA afferents(innervate Ia annulospiral afferents), evoked impulse travels through the dorsal root to the SC, where IA synapses directly on the hononomous(aka motor) anterior horn cells; Anterior horn cells discharge sending impulses to extrafusal m. fibers of the IA’s “parent” or origin m.
H reflex
- only m’s with larger numbers of m. spindles exhibit the H reflex; i.e., ST m’s like the soleus
When would you use the H reflex clinically?
- Evaluates the conductance time required of a peripherally stimulated impulse to travel: Over IA afferents to through the dorsal roots, Across the synapse to alpha MN, then travel distally to the m. through the alpha MN axon
- Most useful to evaluate proximal conduction of IA afferent impulses through the dorsal root to the alpha MNs, which pass out of the S1 foramen to innervate the soleus m.
- Detects nerve root impingements at foramina; Compression at neural foramen causes concurrent slowing of the reflex latency; changes occur 3 weeks sooner than denervation on EMG tests
