EMG and NCV Testing Flashcards
Do you need board certification?
No, only for Medicare reimbursement
Signs & symptoms that warrant electrophysiological testing? (8)
- Paresthesias
- Weakness
- Muscle pain that doesn’t fit pattern of ache/strain
- Neurogenic pain
- h/o trauma or repetitive stress
- Delayed recovery of orthopedic injury (ankle sprain grade 2 & 3) >> Neurogenic inflammation
- Unexpected weakness post surgery
>> Anterior THR Tourniquet, traction
>> Radial artery graft Isolated blood supply to median/ulnar nerves
• Patients with mid-cervical SCI
>> Determine distal nerve integrity prior to undergoing tendon transfers
Electrophysiological testing purposes? (6)
- Identify presence of nerve injury or muscle disease
- Identify which nerve(s) or muscle(s) are damaged
- Characterize injury
>> Fiber types, severity
• Identify where damage is
>> Focus treatment plan
• Determine stage of tissue healing
>> Does not always match time of injury
• Determine prognosis
>> Estimate recovery time
Electrophysiological testing precautions/contraindications? (6)
- Bleeding risk: Pts. on coagulotherapy, platelets < 50,000/mm3
- Infection risk: Lymphedema, immune compromise (HIV or other)
- Specific sites: Pneumothorax, peritoneal insertion, biopsy site
- Avoid stimulation on pts with implanted electrical devices,
- pregnant pts - PATIENT DISCOMFORT!!!!!
Nerve conduction studies (NCS) measure? How?
- Measure how well a peripheral nerve can conduct an induced stimulus = evoked potential
- Electrically stimulate/activate nerve at various points along the superficial path of the nerve & record output at target organ
NCS areas for testing and their corresponding study type? (3)
- Muscle = motor nerve conduction study
- Skin = sensory nerve conduction study
- Proximal nerve components = late responses (H-reflex & f-wave)
NCS measurable characteristics - what is distal latency? Useful for?
• Distal latency – time it takes for electrical signal to reach target tissue from the most distal point of stimulation
- Useful for distal entrapment neuropathies (carpal/tarsal tunnel syndrome)
NCS measurable characteristics - what is conduction velocity? Useful for?
• Conduction velocity – time it takes for electrical impulse to travel between two given points along course of nerve
- Useful for proximal entrapment neuropathies (cubital tunnel syndrome)
NCS measurable characteristics - what is amplitude? Useful for?
• Amplitude – measure of how many working axons are activated when nerve is electrically stimulated
- Useful for systemic conditions (diabetes)
NCS tells us? Helps to?
• Tell us specifically what component of the nerve is injured
- Helps determine prognosis & guide treatment
Latency & velocity are measures of? Speed of a nerve is determined by? What indicates a myelin problem? Slowing identifies what?
- time
- myelin integrity
- Prolonged latency or slow velocity indicates myelin problem
- Slowing identifies where the compression injury is
Amplitude is measure of? Output of nerve is determined by? Low amplitude indicates?
- signal strength
- axonal integrity
- axon problem (most of the time)
Onset/Peak Distal latency = ? Amplitude = ? Velocity = ?
- how fast nerve travels in distal segment
- how many axons are firing when nerve stimulated
- how fast nerve travels btwn limb segments
F/H Latency = ? L-R F/H latency = ?
- how fast nerve travels in entire segment
- how fast nerve travels compared to opposite limb
NCS good for detection of? (4)
- Compression neuropathies (CTS)
- Plexopathies
- Demyelinating polyneuropathies (GBS)
- Neuromuscular junction disorders (Mysethenia Gravis)
NCS poor for detection of? (3)
- Radiculopathies (except H-reflex for S1)
- Myopathies (muscular dystrophy)
- Lower motor neuron disorders (ALS)
EMG determines? It is? Needle acts as? Detecting? Displaying? Examines what? (3)
- Determines the integrity of all components of a motor unit: alpha motor neuron, axon, all muscle fibers innervated by that motor neuron
- Invasive: needled recording electrode inserted through skin and fascia into various depths of the muscle
- Needle acts as antenna, detecting electrical impulses of motor units & displaying as waveforms
- Examines 3 states of the muscle: at rest, with minimal voluntary contraction, increasing effort of voluntary contraction
EMG Resting assessment steps? (3)
- Insert needle into muscle
- Move needle into different depths & quadrants
- Observe electrical activity generated
Normal Resting Assessment - what kind of insertional activity? (2)
- Brief discharge of electrical activity cause by mechanical stimulus of muscle fiber
- Electrical silence after needle stops moving
Abnormal Resting Assessment - decreased insertional activity indicates? Increased?
- Indicates muscle fiber fibrosis/necrosis
- Precursor to spontaneous potentials
Another abnormal resting response? How do they appear?
- Spontaneous potentials
- Sustained waveforms that appear @ rest
Types of spontaneous potentials? (5)
- Fibrilation potentials (Fibs)
- Positive sharp waves (PSW)
- Fasiculation potentials
- Complex repetitive discharges (CRD)
- Myotonic discharges
Fibs and PSW caused by?
Caused by muscle fiber denervation – electrical discharge of muscle fiber w/o input from nerve
Fasiculation Potentials are? Often accompanied by? Only considered abnormal if?
- Spontaneous irregular discharge of motor unit w/o voluntary control
- Often accompanied by visible or palpable muscle twitch
- consistently present and in diffuse muscles of the limbs and/or face
CRD caused by? How do they appear?
- Caused by severe/chronic muscle fiber denervation
- Abruptly start & stop
Myotonic Discharges caused by? How do they appear?
- Caused by muscle fiber’s delayed relaxation
- Wax & wane in amplitude and firing rate
What is an EMG Minimal Contraction Assessment? How do you perform it? Use? (2) They examine? Each one has?
- Gentle, sustained, resisted isometric contraction allows for Motor Unit Action Potential (MUAP) analysis
- Gently move needle close to muscle fiber of active motor unit
- Use auditory & visual feedback
- Examine 12 – 20 different motor units in each muscle • Each MUAP has different shape
Normal MUAP parameters - size = ? Width? Shape? What is it? How many usually?
- Size = Amplitude = 300-8000 microvolts
- Width = Duration = 3-15 ms
- Shape = Phases
- # times waveform crosses baseline
- 2-4 phases
Abnormal MUAP is indicated when?
Size of MUAP does not match muscle effort
EMG moderate to maximal assessment measures? Steps? (2)
- Measures recruitment of motor units
- Without moving needle, ask patient to gradually increase level of effort to maximum
- Observe size and number of motor units
EMG Normal Recruitment presents how? (2)
- As patient contracts stronger, additional MUAP are recruited that are larger than initial one(s)
- All recruited MUAP keep firing to “fill up the screen”
Abnormal Recruitment - Reduced recruitment - presents how? (3)
- Initial MUAP are large
- As effort increases few/no other MUAP activated, existing ones fire faster
Abnormal Recruitment - Rapid recruitment - presents how? (2) Abnormal resting tone = ? Abnormal MUA? Abnormal Recruitment analysis?
- With initial minimal effort, many small MUAP are recruited
- Size or number of MUAP does not increase with increasing effort
- acute axonal damage/denervation
- chronic MU destruction/reorganization
- altered muscle activation
Clinical correlation of abnormal EMG - Decreased insertional activity = ?Fibs/PSW? Fasiculation potentials? CRD?
- neurogenic muscle atrophy
– acute entrapment or systemic axonal neuropathy (abnormal)
– lower motor neuron disorder
– chronic or severe entrapment or systemic axonal neuropathy
Clinical correlation of abnormal EMG - Myotonic discharges? Abnormal MUAP? Reduced recruitment? Rapid recruitment?
– myotonic or muscular dystrophies
– chronic condition with re-innervation
– chronic entrapment or systemic axonal neuropathy
– myopathy
EMG Good for detection of? (3)
- Radiculopathies
- Myopathies (muscular dystrophy)
- Lower motor neuron disorders (ALS)
EMG Poor detection of? (4)
- Compression neuropathies (CTS)
- Plexopathies
- Demyelinating polyneuropathies (GBS)
- Neuromuscular junction disorders (Mysethenia Gravis)
Purpose of EMG/NCS Exam? Basic principles? (3)
- Aid in differential diagnosis of possible neuromuscular disorders
- Maximize true positives and true negatives
- Minimize false positives
- Minimize false negatives
Planning the EMG/NCS Exam principles? (6)
- Take history
- Perform clinical exam •
Establish differential diagnosis/working hypothesis
- Base NCS/EMG on history/exam
- Rule-out with “sensitive” tests
- Rule-in with “specific” tests
EMG/NCV Studies Should be interpreted just like any other? What kind? (3) Referring provider must?
- ancillary tests
- Films
- Labs
- Clinical exam - correlate with other studies and clinical exam
MRI/X-Ray tell us about? NCS/EMG tell us about?
- the structure of the neuromuscular system
• the functional integrity of the neuromuscular system
Testing & Analysis Procedure - select? Compare? (3) Look for?
- Select nerves/muscles to test based on history, clinical exam, & ancillary test findings
- Compare NCS results to published norms and to non-involved limb
- Compare EMG results of suspected muscles to published norms and to non-involved muscles
- Compare values to norms to determine extent and type of injury
- Look for patterns of abnormality to classify injury
What is this?
EMG - normal resting assessment
What is this?
Fibs/PSW
What is this?
CRD
What is this?
Myotonic Discharges
