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Nerve Conduction and Electromyography (EMG)

What are nerve conduction studies?

A nerve conduction study (NCS) is an important test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the human body. It involves the process of applying small electrical impulses to a nerve and recording a response using an electrode. It is a slightly uncomfortable study but in no way harmful to the patient.

Purpose of nerve conduction studies

Mainly used in the evaluation of pareesthesias (sensory symptoms) and/or weakness of the peripheral nerves of the body. The studies conducted are dependent on the presentation of the symptoms.

Common referrals for nerve conduction studies include:

  • Peripheral Neuropathies
  • Carpal Tunnel Syndrome
  • Nerve Compression
  • Guillain-Barré Syndrome
  • Nerve Related Injuries

What studies are performed in NCS

Motor NCS

Motor NCS are performed by electrical stimulation of a peripheral nerve and recording from a muscle supplied by this nerve. The response is then recorded and different aspects of the response are analyzed, namely

  • Latency - Time taking from stimulation to recording site.
  • Amplitudes - Size of the response
  • Conduction velocity - The speed of which the response travels though the nerve.

Sensory NCS

Sensory NCS are performed by electrical stimulation of a peripheral nerve and recording from a purely-sensory portion of the nerve, such as on a finger. Like motor nerve conduction studies the latency, amplitude, and conduction velocity of the response are analyzed.

F-wave study

Is a supramaximal stimulation of a nerve. The study calculates the time it takes from point of stimulation to the anterior horn call and back to recording electrode.

Interpretation of nerve conduction studies

Studies are interpreted by a neurologist. Responses are compared to normal values for specific nerves, and deviations in these values and compared to hallmarks of specific pathological processes.