Nerve Conduction Velocity & Electromyography

Ever stick your finger in a socket? Then you know what nerve conduction testing feels like!! 



Well, sort of. Nerve conduction testing (NCV) is a way to assess the conduction speed of motor and sensory fibers of various nerves.  Electromyography (EMG) is an intramuscular exam that assesses the electrical activity of skeletal muscle fibers.  A neurologist or physiatrist most often order these tests, and can be performed by certified physical therapists.  



NCV is used for to assess peripheral nerve injury (the extent of damage), including peripheral neuropathy, carpal tunnel syndrome, ulnar neuropathy, Guillain-Barre syndrome, Fascuoscapulohumeral muscular dystrophy, spinal disc herniation, cubital tunnel syndrome, tarsal tunnel syndrome, guyon canal syndrome, and peroneal neuropathy.  

EMG is used to assess motor neuron disease, which can occur with a variety of neuropathies and dysfunctions (inherited and acquired syndromes, diseases, or dysfunctions).

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Contraindications

Central nerve injury (NCV does not assess central nerve pathologies, only peripheral nerves; NCV would not be appropriate for assessing multiple sclerosis because this is a central nervous system disease), radiculopathy, patients with impaired cognition, or around open wounds (due to increased risk of infection)

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Precautions

Must still perform a neurological exam (NCV/EMG does not replace a thorough exam)

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Stimulation of peripheral nerves at specific, measured segments is performed via electrodes (ring electrodes for sensory, blocked electrode for motor), and results are recorded and analyzed by a computer system.  



​Latency- time for tingling or contraction to occur after stimulation is applied

​Velocity- distance divided by latency

​Amplitude is determined by the power needed to reach maximal intensity of the sensory or motor nerve. 



Normative values are used to determine significance of findings, and can help determine the focal area of a specific lesion. 

 

MEDIAN MOTOR

Stim Site     End Site        Distance               Time to Onset      Amplitude
Wrist              APB                 8cm                      Latency: 4ms         5mV
Elbow           Wrist          Depends on pt         NCV: 50m/s           5mV
Axilla             Elbow        Depends on pt          NCV: 50m/s          5mV



MEDIAN SENSORY

Stim Site        End Site      Distance           Time to Onset       Amplitude
Palm              2nd Digit          7cm                Latency: 1.7ms         15uV
Wrist             2nd Digit         14cm               Latency: 4ms            15uV
Wrist               Palm                7cm                  NCV: 40m/s             15uV
Elbow             Wrist      Depends on pt        NCV: 50m/s             15uV
Axilla              Elbow     Depends on pt        NCV: 50m/s             15uV



ULNAR MOTOR

Stim Site        End Site           Distance           Time to Onset       Amplitude
Wrist               AbDM                  8cm                  Latency: 4ms           5mV
Below Elbow  Wrist           Depends on pt      NCV: 50m/s              5mV
Above Elbow    BE              Depends on pt      NCV: 45m/s             5mV
Axilla                  AE              Depends on pt      NCV: 50m/s             5mV



ULNAR SENSORY

Stim Site        End Site           Distance           Time to Onset       Amplitude
Palm              5th Digit               7cm                Latency: 1.7ms          15uV
Wrist             5th Digit             14cm                Latency: 4ms             15uV
Wrist                Palm                  7cm                    NCV: 40m/s             15uV
Below Elbow  Wrist          Depends on pt        NCV: 50m/s             15uV
Above Elbow   BE             Depends on pt         NCV: 45m/s             15uV
Axilla                 AE             Depends on pt         NCV: 50m/s             15uV



(*Wrist to palm velocity should be 40m/s)