Sudomotor function assessment:

Nerve Conduction Velocity (NCV) Test

What is it?

A nerve conduction velocity test, also called a nerve conduction study, measures how quickly electrical impulses move along a nerve.

A healthy nerve conducts signals with greater speed and strength than a damaged nerve. The speed of nerve conduction is influenced by the myelin sheath — the insulating coating that surrounds the nerve.

Most neuropathies are caused by damage to the nerve’s axon rather than damage to the myelin sheath surrounding the nerve. The nerve conduction velocity test is used to distinguish between true nerve disorders (such as Charcot-Marie-Tooth disease) and conditions where muscles are affected by nerve injury (such as carpal tunnel syndrome).

Why should I do it?

This test is used to diagnose nerve damage or dysfunction and confirm a particular diagnosis. It can usually differentiate injury to the nerve fiber (axon) from injury to the myelin sheath surrounding the nerve, which is useful in diagnostic and therapeutic strategies.

How is it performed?

During the test, flat electrodes are placed on the skin at intervals over the nerve that is being examined. A low intensity electric current is introduced to stimulate the nerves.

The velocity at which the resulting electric impulses are transmitted through the nerves is determined when images of the impulses are projected on an oscilloscope or computer screen. If a response is much slower than normal, damage to the myelin sheath is implied. If the nerve’s response to stimulation by the current is decreased but with a relatively normal speed of conduction, damage to the nerve axon is implied.

How will it feel?

There is generally minimal discomfort with the test because the electrical stimulus is small and usually is minimally felt by the patient.

Quantitative Sensory Testing (QST)

What is it?

Quantitative sensory testing (QST) is a method used to assess damage to the small nerve endings, which detect changes in temperature, and the large nerve endings, which detect vibration

Why do it?

QST is used to diagnose and assess the severity of nerve damage, especially in the small nerve endings. It can also help determine if a neuropathy is responding to treatment. It is used to diagnose many different types of neuropathies, including peripheral neuropathies. It may also be used to identify where the nerves are damaged.

How is it performed?

QST uses a computer testing system to measure how the nerves involved react to vibration and changes in temperature. The test results are compared to a series of “normal” patients as well as to the patient’s unaffected side.

How will it feel?

Depending on the specific test, the patient will feel mild vibrations and hot and cold sensations. The procedure is non-invasive — no needles are used. Overall, little or no discomfort should be felt during the test.

Epidermal Nerve Fiber Density (ENFD) is a technology used by neurologists for over 15 years. This diagnostic modality takes advantage of the fact that most forms of peripheraly neuropathy progress in a distal to proximal fashion, beginning with the body’s smallest and most distal (foot) nerve twigs (C fibers and A delta fibers), and then progressing proximally. This is why our diabetic patients so often present with peripheral neuropathy in a “stocking-like” distribution, i.e. in the feet. Those patients that exhibit this form of neuropathy, without involvement of larger and more proximal nerves, are said to have small fiber peripheral neuropathy. If the pathological process moves to the larger nerves, the neuropathy becomes mixed.

In short, ENFD testing measures the amount of C-fibers and A-delta fibers via a 3mm punch biopsy of the skin. With this testing, the physicians at OCFA can determine the amount of damage present as well as determine the degenerative changes present which may be predicative of impending neuropathy even before symptoms begin.