A nerve conduction study (NCS) is used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves of the body.
It helps to evaluate the motor and sensory nerves by measuring Nerve conduction velocity (NCV).
It, along with needle electromyography measure nerve and muscle function, and may be indicated when there is pain in the limbs, weakness from spinal nerve compression, or concern about some other neurologic injury or disorder.
Spinal nerve injury does not cause neck, mid back pain or low back pain, and for this reason, evidence has not shown
EMG or NCS is not helpful in diagnosing causes of axial lumbar pain, thoracic pain, or cervical spine pain, as spinal nerve injury is not associated with pain.
Nerve conduction studies are used mainly for evaluation of paresthesias and/or weakness of the arms and legs.
Disorders diagnosed by nerve conduction studies include:
Carpal tunnel syndrome
Cubital Tunnel Syndrome
Guillain–Barré syndrome
Guyon’s canal syndrome
Peripheral neuropathy
Peroneal neuropathy
Spinal disc herniation
Tarsal Tunnel Syndrome
Ulnar neuropathy
NCS involves Motor NCS, Sensory NCS, F wave study and H-reflex study.
NCS is often combined with needle electromyography.
Motor NCS involves electrical stimulation of a peripheral nerve and recording from a muscle supplied by this nerve.
The time it takes for the electrical impulse to travel from the stimulation to the recording site is the latency period, and is measured in milliseconds (ms).
The amplitude is also measured in millivolts (mV).
Sensory NCS are performed by electrical stimulation of a peripheral nerve and recording from a purely sensory portion of the nerve.
Sensory latencies are measured on the scale of milliseconds.
Sensory amplitudes are much smaller than the motor amplitudes, usually in the microvolt (μV) range.
F-wave study uses supramaximal stimulation of a motor nerve and recording of action potentials.
The F-wave latency can be used to derive the conduction velocity of nerve between the limb and spine, whereas the motor and sensory nerve conduction studies evaluate conduction in the segment of the limb.
H-reflex study uses the stimulation of a nerve and recording the reflex electrical discharge from a muscle in the limb.
It also evaluates conduction between the limb and the spinal cord
The afferent impulses are in sensory nerves while the efferent impulses are in motor nerves.
NCS can determine the presence of nerve impingement within the nerve root level where EMG tests fail.
NCS objectively measures the amplitude of the action potential at a distant site along the nerve being tested.
Measurement of nerve recruitment for surrounding nerves is displayed.
Non impinged nerves do not recruit surrounding nerves and this is readily seen on the display.
Small fiber NCS has over 95% accuracy for determining the spine level(s) and side(s) for Small Pain Fiber impingement/pathology.
Small fiber NCS allows for the most accurate diagnosis and treatment procedures for patients experiencing back pain.
Patients diagnosed with the EMG/NCV studies alone are misdiagnosed in over 50% of cases including the diagnosis and treatment of incorrect nerve root levels and sides in patients.
Different pathological processes result in changes in latencies, motor, and/or sensory amplitudes, or slowing of the conduction velocities to differing degrees.
The slowing of the NCV usually indicates there is damage to the myelin.
Slowing across the wrist for the motor and sensory latencies of the median nerve indicates focal compression of the median nerve at the wrist, called carpal tunnel syndrome.
Slowing of all nerve conductions in more than one limb indicates generalized diseased nerves, or generalized peripheral neuropathy, as seen in diabetes mellitus.
Patients with a permanent pacemaker or other such implanted stimulators such as deep brain stimulators or spinal cord stimulators need special precautions.
Cardiac pacemakers and implanted cardiac defibrillators (ICDs) have theoretical concerns that electrical impulses of nerve conduction studies (NCS) could error oneously sensed by devices and result in unintended inhibition or triggering of output or reprogramming of the device.