Archive for February, 2013

Nerve Conduction Studies for diagnosing foot conditions

February 2, 2013

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The human nervous system is an amazingly sophisticated network that coordinates all the functions of the body.  In order for the system to relay information, the brain must send a signal to the organ(s) needed to complete the desired function.  This system of communication between the brain and body is made up of two major divisions:  the central nervous system and the peripheral nervous system.

The central nervous system consists of the brain and spinal cord.  The brain is responsible for conscious decisions and controls a majority of the bodily functions.  The spinal cord functions to relay information from the brain to the peripheral nervous system, and is also responsible for many of the body’s inherent reflexes.

The peripheral nervous system is made up of all the nerves extending from the spinal cord to the various organs of the body.   These nerves can have motor, sensory, autonomic, or “mixed” functions.  Motor nerves are fibers intended to control some form of muscle movement.  Sensory nerves are responsible for our sense of pain, temperature, and vibration as well as other forms of the body’s interaction with the environment.  Functions that we are not normally in conscious control of (such as heart rate, digestion, and breathing) are controlled by autonomic nerve fibers.  Nerves with “mixed” functions can contain signals from any combination of these three types.

There are many diseases that can affect the normal functioning of the nervous system.  A nerve conduction velocity test (NCVT) is very useful in the evaluation of various forms of nerve damage and disease.

What do Nerve Conduction Velocity Studies measure?

Communication sent along nerve fibers takes the form of an electrical signal, and travels much like electrical current moving through a wire.  NCVT is used to measure the speed at which the nerve signal travels along a specific nerve fiber.  This technique can be used to study the function and health of both sensory and motor nerves.  Autonomic and “mixed” are not as useful to study in a clinical setting, and so are not examined with this technique.

How is the NCVT performed?

In order to test a nerve, two electrodes are placed over a segment of the nerve and an electrical current is generated that travels between them.  One electrode is responsible for producing the current, and the second electrode detects the electrical impulse as it travels along the nerve.  The nerve conduction velocity is then calculated using the distance between the two electrodes and the time needed for the signal to travel between them.      

Preparation Pain and Risks of the procedure

The day of the procedure you should avoid using any lotion or cream on your feet and legs.

Wear loose fitting pants/cloths that can be rolled up above the knees.

The test should take about 30 minutes and is done in the doctors office.

There are essentially no risks involved in NCVT.  The nerve signals can be measured on the surface of the skin using surface electrode probes.  Testing has been proven to be safe even for patients with pacemakers and other health related electrical implants, especially when being performed on the lower body. 

Why do you have this test?

If your doctor suspects your foot condition may be a result of nerve damage or blockage a NCVT may be needed to make the proper diagnosis. The symptoms in your foot that may indicate such nerve involvement could include numbness, weakness, tingling, burning and or cramps.

Your doctor maybe ruling out such nerve conditions as Tarsal tunnel syndrome, nerve entrapment, diabetic neuropathy, peripheral neuropathy or ridiculopathy.                                                           

 After the test is done you can return immediately to normal activities.

The results are calculated and will be reviewed at your next office visit.

 

 

Source Material

Al-Shekhlee, A; Shapiro, BE; Preston, DC. Iatrogenic complications and risks of nerve conduction studies and needle electromyography. Muscle Nerve. 2003;27(5):517.

Erlanger, J; Gasser, HS. Electrical signs of nervous activity, University of Penn Press, Philadelphia, PA 1937.

Landau, ME; Diaz, MI; Barner, KC; Campbell WW. Optimal distance for segmental nerve conduction studies revisited. Muscle Nerve. 2003;27(3):367.

Liddell, EGT; Sherrington, CS. Recruitment and some other factors of reflex inhibition. Proc R Soc Lond [Biol]. 1925; 97:488.

Nandedkar, SD; Barkhaus, PE. Contribution of reference electrode to the compound muscle action potential.  Muscle Nerve. 2007;36(1):87.

Phongsamart, G; Wertsch, JJ; Ferdjallah, M; King, JC; Foster, DT. Effect of reference electrode position on the compound muscle action potential (CMAP) onset latency. Muscle Nerve. 2002;25(6):816.

Schoeck, AP; Mellion, ML; Gilchrist, JM; Christian, FV. Safety of nerve conduction studies in patients with implanted cardiac devices. Muscle Nerve. 2007;35(4):521

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