Diagnostic EMG

Question 1

Electrodiagnosis (EDX) studies includes

Answer 1

NC - nerve conduction studies
EMG - elecromyography
Often both are referred to as an EMG

Question 2

Entire purpose of EDX is to determine

Answer 2

Is there a problem in the peripheral nervous system

AND if so, where it the problem occurring

Question 3

EMG and NCS are extensions of

Answer 3

the neuro and musculoskeletal exam

Question 4

EDX needs to be interpreted in accordance with

Answer 4

the entire clinical picture
It is a complete exam, not simply a test
The more you know about basic anatomy of the nerves and mm, the easier it will be to learn about and interpret EDX

Question 5

EDX - history

Answer 5

Originated 19th century
Only consistently used in past 30-40 yrs
First machine had no screens, only speakers

Question 6

People who perform EDX

Answer 6

Physiatrists
Neurologists
PT/Technicians `

Question 7

Why do EDX studies

Answer 7

To distinguish between many peripheral and mm disorders
Represents a physiologic piece of the diagnostic puzzle - real time info about what is happening physiologically with respect to the nerve and mm

Question 8

EDX vs. MRI

Answer 8

EMG will tell you where the problem is, but not exactly what is causing it
MRI will help you determine what is causing it

Question 9

EDX studies are used to

Answer 9

1 Establish correct dx
2 Localize the lesion
3 Determine tx if dx is already known
4 Provide info about prognosis

Question 10

If you suspect an L5 radiculopathy in your pt, which test will you order to view the possible pathology

Answer 10

MRI

Question 11

If you suspect an L5 radiculopathy in your pt, which test will you order to objectively demonstrate physiological changes in the nerve or muscle

Answer 11

EMG

Question 12

Wallerian Degeneration - define

Answer 12

Degenerative changes that occur in the distal axonal segments and their myelin sheath secondary to proximal axonal injury or death of the cell body

Question 13

Neurapraxia

Answer 13

Failure of nerve conduction across the affected nerve segment combined with normal nerve conduction above and below the segment
NO WALLERIAN DEGENERATION INVOLVED

Question 14

Axonotmesis

Answer 14

Disruption of axon continuity with Wallerian degeneration, but perineurium and/or endoneurium are still intact
Destroy the axon but there is still stuff around it that is intact

Question 15

Neurotmesis

Answer 15

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

Question 16

What type of nerve injury has Wallerian degeneration but still has perineurium and/or endoneurium intact

Answer 16

axonotmesis

Question 17

Common reasons for NCS/EMG - Symptoms

Answer 17

N/T
Extremity or radicular pain
Weakness

Question 18

Common reasons for NCS/EMG - Physical findings

Answer 18

Reflex loss or asymmetry
Weakness
Sensory loss 
Limp 
MM atrophy

Question 19

Timing - when to do EDX studies - Main rule of thumb -

Answer 19

EMG or NCS should not be performed prior to 21 days after the injury or onset of symptoms
Very few exceptions to this rule

Question 20

Contraindications - Strict

Answer 20

1 Sever bleeding disorder/Anticoagulation out of control
2 NCS contraindicated with automated implanted cardiac defibrillator
3 Active skin/soft tissue infection

Question 21

Relative contraindications

Answer 21

In extremity of someone who has undergone axillary lymph node dissection
Pt needed mm biopsy

Question 22

Complications

Answer 22

Infection
Bleeding
Accidental penetration of the needle into something other than intended muscle

Question 23

Good criteria for ordering or performing

Answer 23

Is the test necessary
Will it help you determine dx, tx, or prognosis
Is there a test less intrusive and may be more cost effective that can provide the same info

Question 24

You have a 66 y/o patient reporting stocking and glove distribution of numbness and tingling in the limbs and history of diabetes, now on treatment with insulin
- do you order EDX

Answer 24

Based on hx alone seems like diabetic peripheral neuropathy

But you don’t know for sure until go through exam

Question 25

Interpretation - How do you explain a normal EDX exam

Answer 25

Normal EDX does not necessarily mean normal function or that the patient's symptoms have no physiologic basis May mean that the sensitivity and specificty of the exam can't define a specific problem by available techniques

Question 26

Interpretation of EDX - normalized values

Answer 26

Different labs have different normalized values

Question 27

How we would explain a normal (or negative) EDX study to a patient who has positive signs and symptoms (i.e. Tinel’s, paresthesias, etc.) in layman's terms

Answer 27

“The nerve may be compressed and cause signs and symptoms but not enough to damage the ‘wiring’ or ‘coating’ around the wiring of the nerves.”

Question 28

EDX Results are dependent on what

Answer 28

Examiner dependent! Vary with technique, ability, and thoroughness of the examiner Technical error is the most important factor leading to incorrect conclusions about the data obtained

Question 29

Types of nerve conduction studies

Answer 29

Motor nerve conduction Sensory nerve conduction Both study waveforms generated in the peripheral nervous system

Question 30

Types of nerve conduction studies - motor nerve conduction

Answer 30

- Compound Motor Action Potential (CMAP) | - Stimulation of a peripheral nerve while recording from a muscle innervated by that nerve

Question 31

Nerve conduction studies - sensory nerve conduction

Answer 31

- Sensory Nerve Action Potential (SNAP) | - Stimulation of a sensory (cutaneous) or mixed nerve while recording from a mixed or cutaneous nerve

Question 32

NCS Latency

Answer 32

Interval between the onset of a stimulus and the onset of a response

Question 33

NCS Amplitude

Answer 33

Maximum voltage difference between two points | Proportional to number and size of nerve fibers that are depolarized

Question 34

NCS amplitude provides an estimate of the

Answer 34

amount of nerve tissue that is electrically active (estimate of axons conducting electricity)

Question 35

NCS - Conduction velocity

Answer 35

The “speed” at which the nerve fibers are carrying the electrical stimulus between two sites V = distance/time

Question 36

NCS - Conduction velocity - comparison of conduction between two segments of the same nerve can

Answer 36

localize a lesion

Question 37

NCS - Late responses

Answer 37

(F wave & H reflex) Most useful for detecting proximal nerve pathologies Especially early in disease (like GB)

Question 38

NCS - H Reflex

Answer 38

Due to a monosynaptic spinal reflex Primary value of the H reflex is in distinguishing S1 from L5 radiculopathies H reflex will be abnormal in an S1 radiculopathy `

Question 39

Elecromyography

Answer 39

The electric activity recorded by a needle electrode in muscle fibers during firing singly or in groups near the electrode

Question 40

EMG - Insertional activity

Answer 40

The sound you hear when you insert the needle in - there is a normal sound and an abnormal one

Question 41

EMG - Spontaneous activity

Answer 41

Activity that happens without the patient moving their muscle

Question 42

EMG - Voluntary Activity

Answer 42

Ask the patient to contract/move their muscle and look at the Motor Unit Action Potentials Amplitude, Duration, Recruitment

Question 43

EMG - Spontaneous Activity can include

Answer 43

``` Fibrillation potentials Positive sharp waves Fasciculation potentials (common with ALS) Myotonic discharges Complex repetitive discharges Myokymic discharges Cramps Neuromyotonic discharge ```

Question 44

Radiculopathy - NCS

Answer 44

Main reason for NCS in this case is to rule out other pathologies

Question 45

Radiculopathy - NCS - Sensory NCS in a radiculopathy study

Answer 45

Majority are normal Damage is proximal to the DRG therefore the axon is still intact with its cell body and no Wallerian deg. takes place If sensory NCS is abnormal, we look for other pathology

Question 46

Radiculopathy - NCS - Motor NCS

Answer 46

May be normal | In a severe radicular lesion the axon loss can lead to Wallerian degeneration and th CAMP amplitude may be reduced

Question 47

Radiculopathy - EMG

Answer 47

Most useful procedure in localizing radiculopathy and predicting prognosis

Question 48

Radiculopathy - EMG - most objective evidence of acute denervation

Answer 48

Presence of spontaneous activity (fibrillations, PSW) Begins in the proximal paraspinal mm within 5-7 days of compression Limb mm show spont activity within 3 weeks

Question 49

Radiculopathy - EMG - choice of mm

Answer 49

Is critical! | Typical screen will be modified based on abnormal findings on the physical exam

Question 50

Radiculopathy - NCS findings

Answer 50

Normal SNAP amp | Normal CMAP amp

Question 51

Radiculopathy - EMG findings

Answer 51

Spontaneous potentials (fibs and PSWs) in the paraspinal mm and two mm from different peripheral nerves innervated by the same affected root level

Question 52

NCS and needle EMG are great studies because

Answer 52

they provide information about the injured or diseased nerves' pathophysiology (demyelination and/or axonal loss, or complete severing of nerve)