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Neuro Behavioral Med I > 9 - Electrodiagnostic Studies > Flashcards

9 - Electrodiagnostic Studies Flashcards

1
Q

What is an EMG?

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A

Entire purpose of electrodiagnostic studies is to determine:

  • Is there a problem in the peripheral nervous system (AND)
  • If so, where is the problem occurring
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2
Q

What does an electrodiagnostic study include?

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A

Most commonly includes

  • NCS: Nerve conduction studies
  • EMG: Electromyography
  • Often we refer to both as “EMG”
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3
Q

What is the use of EMG and NCS studies?

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A
  • EMG and NCS are extensions of the neurological and musculoskeletal examination
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4
Q

What are the key points about EMB and NCS?

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A
  • Electrodiagnosis is a complete examination, not simply a test and must be interpreted in accordance with the entire clinical picture
  • The more you know about the basic anatomy of the nerves and muscles, the easier it will be to learn about and interpret electrodiagnostic studies
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5
Q

Why do we do EDX studies?

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A
  • Important method to distinguish between many peripheral nerve and muscle disorders
  • Another ‘piece’ to put the puzzle together
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6
Q

What does the EDX study tell you?

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A
  • Represent a physiologic piece of the diagnostic puzzle
  • Real time information about what is happening physiologically with respect to the nerve and muscle ***
  • (Unlike MRI, CT, XR; which are sophisticated photographs that show anatomy)
  • *** These tests all complement each other and each has a role in establishing the correct diagnosis in neuromuscular disorders
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7
Q

What are the common reasons for an NCS/EMG?

A

Symptoms

  • Numbness/tingling
  • Weakness
  • Extremity or radicular pain

Physical findings

  • Reflex loss or asymmetry
  • Weakness
  • Sensory loss (Touch, Temperature, Proprioceptive)
  • Limp
  • Muscle atrophy
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8
Q

What are some uses of EDX studies?

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A
  • Establish the correct diagnosis
  • Localize the lesion
  • Determine treatment if the diagnosis is already known
  • Provide information about prognosis
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9
Q

Review question: if you suspect an L5 radiculopathy in your patient, which test would you order to view possible pathology?

a. CT Scan
b. EMG/NCS
c. MRI
d. Plain films (XR)
e. Ultrasound

A
  • View possible pathology - MRI or maybe CT scan if you can’t get an MRI right away
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10
Q

Review question: if you suspect an L5 radiculopathy in your patient, which test would you order to objectively demonstrate physiologic changes in the nerve or muscle?

a. CT Scan
b. EMG/NCS
c. MRI
d. Plain films (XR)
e. Ultrasound

A
  • To objectively demonstrate physiologic changes in the nerve or muscle - EMG/NCS
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11
Q

What is the timing or when you should perform an EDX study?

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A
  • In most cases EMG or NCS should NOT be performed prior to 21 days after the injury or onset of symptoms
  • Axonal nerve injury can slowly spread down the entire length of the nerve
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12
Q

What is a myelinated nerve composed of?

A
  • A myelinated nerve is composed of an axon and it’s surrounding myelin nerve sheath
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13
Q

What is myelin?

A
  • Connective covering surrounding motor nerve axons and many sensory nerve axons
  • Produced by Schwann cells
  • Functions to greatly increase the speed of nerve conduction through saltatory conduction.
  • Injury due to demyelination can be focal or diffuse
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14
Q

What is an axon?

A
  • The usually long process of a nerve fiber that generally conducts impulses away from the body of the nerve cell
  • Injury to the axon causes Wallerian Degeneration
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15
Q

What is Wallerian degeneration?

A
  • Degenerative changes which occur in the distal axonal segments and their myelin sheath secondary to proximal axonal injury or death of the cell body
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16
Q

What are the types of nerve injuries?

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A

Seddon classification system

  • Neurapraxia
  • Axonotmesis
  • Neurotmesis
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17
Q

Describe a neuropraxia nerve injury

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A
  • Failure of nerve conduction across the affected nerve segment combined with normal nerve conduction above and below the segment
  • No Wallerian degeneration involved
  • Carries good prognosis
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18
Q

Describe an axonotmesis nerve injury

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A

Disruption of axon continuity with Wallerian degeneration, but perineurium and/or endoneurium are still intact

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19
Q

Describe a neurotmesis nerve injury

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A

Severance of nerve; carries poor prognosis and surgical repair is needed for functional recovery

20
Q

What type of nerve injury (Seddon classification) has Wallerian degeneration but still has perineurium and/or endoneurium intact?

a. Axonotmesis
b. Neurapraxia
c. Neurotmesis

A

a. Axonotmesis

21
Q

What are the criteria for ordering or performing a NCS/EMG study?

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A
  • Is the test necessary?
  • Will it help you determine the diagnosis, treatment, or prognosis of a patient?
  • Is there a test that is less intrusive and may be more cost-effective that can provide the same information?
22
Q

What are the contraindications of NCS/EMG studies?

A
  • Bleeding disorder - can’t use needles
  • Cardiac defibrillator - avoid this area
  • Active skin infection (cellulitis) - avoid this area
23
Q

How common are complications in NCS/EMG studies?

A

RARE

  • Infection, bleeding
  • Accidental penetration into something other than muscle (most common)
24
Q

What is the take home message about EDX studies?

A

EDX studies are sometimes essential in establishing a particular diagnosis…Sometimes not useful at all

25
Q

Review: criteria for ordering

IMPORTANT ***

A

REVIEW: CRITERIA FOR ORDERING

  • Establish the correct diagnosis
  • Localize the lesion
  • Determine treatment if the diagnosis is already known
  • Provide information about prognosis
26
Q

What is the purpose of nerve conduction studies?

A

Purpose:

  • Determine if there is pathology of the nerve or nerves
  • And if so, at what level the pathology originates
27
Q

What do we see when doing a nerve conduction study?

A

Studies of the waveforms generated in the peripheral nervous system

  • Motor nerve conduction (CMAP) = Stimulation of a peripheral nerve while recording from a muscle innervated by that nerve
  • Sensory nerve conduction (SNAP) = Stimulation of a sensory (cutaneous) or mixed nerve while recording from a mixed or cutaneous nerve
28
Q

What will we look at in terms of latency?

A

Interval between the stimulus and the onset of a response

29
Q

What will we look at in terms of amplitude?

A
  • The maximum voltage difference between two points
  • It is proportional to the number and size of nerve fibers that are depolarized
  • Provides an estimate of the amount of nerve tissue that is electrically active
30
Q

What will we look at in terms of conduction velocity?

A
  • The “speed” at which the nerve fibers are carrying the electrical stimulus between two sites
  • Comparison of conduction between two segments of the same nerve can localize a lesion, i.e.:
31
Q

What factors can affect conduction?

A
  • Age (children)

- Temperature

32
Q

What will we look at in terms of late responses?

A
  • F wave and H reflex
  • Most useful for detecting proximal nerve pathologies
  • Especially early in disease
33
Q

What will we look at in terms of H-reflex?

A
  • Due to a monosynaptic spinal reflex
  • Primary value is in distinguishing S1 from L5 radiculopathies
  • Often this is difficult with physical exam and even EMG as L5 and S1 have overlapping myotomes
  • However, in an S1 radiculopathy, the H reflex will be abnormally slow when compared to non-involved limb
34
Q

What is an EMG study?

A
  • Electric picture of the muscle
  • The electric activity recorded by a needle electrode in muscle fibers during firing singly or in groups near the electrode
  • Firing (def): voluntary or involuntary muscle contraction
  • Displays a ‘real-time’ picture (on screen) and a sound (speaker) of the electrical activity of the muscle membrane
  • Needle acts like an antenna
35
Q

What are the three types of activity you could detect on an EMG?

A
  • Voluntary activity
  • Insertional activity
  • Spontaneous activity
36
Q

Describe voluntary activity

A

Voluntary activity

  • Appearance of the motor unit action potential (MUAP)
  • One axon and all its muscle fibers
37
Q

Describe insertional activity

A
  • Electrical activity caused by insertion or movement of a needle electrode
  • The amount of activity may be described as ‘normal, increased or reduced’

Possible findings

  • Increased (Denervated muscle, myopathies)
  • Reduced (Replacement by fat or connective tissue)
38
Q

Describe spontaneous activity

A

PATHOLOGIC

  • Abnormal electrical activity at rest
  • Fibrillation potentials *
  • Positive sharp waves *
  • Fasciculation potentials
  • Myotonic discharges
  • Complex repetitive discharges
  • Myokymic discharges
  • Cramps
  • Neuromyotonic discharges
39
Q

Describe what the results of an EDX study depend on

A

EDX studies are examiner-dependent

  • Vary with the technique, ability, and thoroughness of the examiner
  • The yield of NCS and EMG is improved when the tests are meticulously performed
  • Technical error is the most important factor leading to incorrect conclusions about the data obtained
40
Q

How do you describe EDX to patients?

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A

There are two main points

  • Nerve conduction studies (NCS)
  • Needle electromyography (EMG)
41
Q

How do you describe NCS to patients?

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A

With the nerve conduction studies, nerves will be stimulated (or shocked) and recorded with surface electrodes.

42
Q

How do you describe EMG to pateints?

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A

With the EMG, muscle membrane activity will be evaluated at rest and with contraction with a needle inserted into the muscle

43
Q

How do you interpret a “normal” EDX exam?

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A
  • Do not necessarily mean normal function or that the patient’s symptoms have no physiologic basis
  • May mean that the sensitivity and specificity of the exam cannot define a specific problem by available techniques
44
Q

How do you explain a normal EDX exam to the patient?

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A

“The nerve may be compressed and cause signs and symptoms (i.e. Tinel’s, paresthesias, etc.) but not enough to damage the ‘wiring’ (axons) or ‘coating’ (myelin) around the wiring of the nerves.”

45
Q

Here is a REVIEW: what are good criteria for ordering or performing an EDX?

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*** third time on slides **

A
  • Is the test necessary?
  • Will it help you determine the diagnosis, treatment, or prognosis of a patient?
  • Is there a test that is less intrusive and may be more cost-effective that can provide the same information?
46
Q

CONCLUSION ***

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A

NCS and needle EMG are great studies because they provide information about the injured or diseased nerves’ pathophysiology (demyelination and/or axonal loss, or complete severing of nerve)

47
Q

What should you REMEBER?

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A
  • It provides no specific information as to what is causing the disease or injury
  • This is another ‘piece of the puzzle’
  • It must be interpreted in accordance with the entire clinical picture (history, physical, imaging studies, labs, etc.)

Neuro Behavioral Med I (15 decks)

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