Electrodiagnostic testing: Electromyography (EMG) and Nerve conduction studies (NCS)

Question 1

Electrodiagnostic testing includes

Answer 1

• EMG and NCS
• is only PART of the full examination

Question 2

What should a FULL neuromuscular exam include

Answer 2

• EMG/NCS
• patient HX
• pain assessment
• MMT
• sensation testing
• reflexes
• evaluation of functional abilities
• visual inspection (atrophy, trophic changes ETC)

findings are not diagnostic & must be considered w/ other findings

Question 3

What is EMG testing

Answer 3

• cannot be used to evaluate CNS function
• examines the electical signal of a muscle via insertion of a small needle into the muscle

Question 4

What is a nerve Conduction study

Answer 4

• assesses the speed and signal of peripheral motor and sensory nerves in the extremeties

Question 5

What can both and EMG and NCS assist with diagnosis of

Answer 5

• mononeuropathy (carpal tunnel)
• plexopathy (brachial plexus injury)
• radiculopathy (from one section of the spine
• poly neuropathy (diabetic GBS)
• muscular dystrophy
• Motor Neuron Disease: (ALS)
• Myotonic disease (myotonic dystrophy)
• neuromuscular junction disorders (myoasthenia gravis)

Question 6

EMG allows what

also what can the test determine

Answer 6

• allows use to record the electrical activity of muscle based on the activity of motor unit
• differentiates between denervated muscle and myopathy
• EMG can determine whether a lesion is neurogenic or myopathic but is NOT capable of determining the actual disease.

Question 7

EMG exam

Answer 7

• EMG measures muscle activity at rest and with contraction
• electrode is inserted directly into muscle
• single axon conducts an impulse to all its muscle fibers causing them to depolarize
• this depolarization produces electrical activity that is manifested as a motor unit action potential
• Needle is moved to different areas and depths of muscle to sample different muscle fibers and motor units
• this is necessary because of the small area from which a needle electrode will pick up electrical activity and because effects of pathology may vary within a single muscle
• up to 25 points within a muscle may be examined by moving and reinserting the electrode

Question 8

What should the EMG look like at different point

Answer 8

• when the muscle is at rest there should be no muscle activity that is seen or heard
• when the muscle is contracting you can see or hear it

Question 9

Nerve Conduction Study

What does it differentiate amoung

Answer 9

• determines the speed with which a peripheral motor or sensory nerve conducts an impulse and the amplitdue of the signal
• Nerve conduction studies differentiate amoung nerve, NMJ, and muscle disorders
• if they have a myopathy then this test should be normal

Question 10

how is speed and amplitude measured during an NCS

Answer 10

• speed: latency (how long does it take from the onset of stimulus until they see it on machine - how long it takes to respond) and conduction velocity (meters/second)
• speed is relate to myelin
• amplitude is a measure of the axon and how intense the signal is

Question 11

What nerves can be testing with NCS

Answer 11

• NCV can be tested on any peripheral nerve that is superficial enough to be stimulated through the skin at two differnet points
• most commonly tested motor nerves = ulnar, median, fibular, tibial, radial, femoral, sciatic
• most commonly tested sensory nerves are median, ulnar, radial, sural and superficial fibular nerves

Question 12

How does an NCS exam work

Answer 12

• stimulating electrodes are placed on skin overlying a nerve
• recording electrodes are placed either at a different point over the same nerve or overlying a muscle innervated by that nerve
• pt is stimulated 1st distally then proximally