A Nerve Conduction Velocity (NCV) test assesses the function of peripheral nerves by evaluating how quickly electrical signals travel through them. This helps healthcare providers identify potential nerve damage or dysfunction. The NCV test provides insights into the health of nerves that extend from the spinal cord to the rest of the body, allowing for movement and sensation.
How Nerves Transmit Signals
Nerves function like biological electrical wires, transmitting messages throughout the body. These messages are electrical impulses, known as action potentials, which travel rapidly along nerve cells called neurons. The speed at which these signals move is referred to as conduction velocity. Some nerve fibers are covered by a fatty insulating layer called myelin, which helps signals travel much faster along the nerve.
There are two main types of nerves involved in this communication: sensory nerves and motor nerves. Sensory nerves transmit information from sensory receptors, such as those in the skin, eyes, and ears, towards the brain and spinal cord, enabling perception of touch, pain, and other sensations. Conversely, motor nerves carry commands away from the brain and spinal cord to muscles and glands, enabling movement and bodily functions.
Reasons for an NCV Test
A doctor may recommend an NCV test if an individual experiences symptoms suggesting nerve involvement. Common symptoms include numbness, tingling sensations, pain, muscle weakness, or muscle cramping.
These include conditions like nerve entrapment, where a nerve is compressed, as seen in carpal tunnel syndrome. It can also help evaluate nerve damage resulting from underlying health conditions such as peripheral neuropathy, Guillain-Barré syndrome, or a herniated disc. The test is often used to distinguish between a nerve disorder and a muscle disorder.
The NCV Test Process
Patients are usually advised to avoid applying lotions, creams, or oils to their skin for a few days before the procedure, as these can interfere with electrode placement. It is also important to maintain a normal body temperature, as low temperatures can slow nerve conduction and affect results. Individuals with implanted electrical devices, such as pacemakers, should inform their healthcare provider.
During the test, surface electrodes, which are adhesive patches, are placed on the skin over the nerves or muscles to be examined. A mild, brief electrical impulse is delivered through one electrode to stimulate the nerve. Another electrode records the resulting electrical activity and the time it takes for the signal to travel. While the electrical impulses may cause a sensation similar to a quick zap or tingling, the test is generally well-tolerated and typically not painful. The entire procedure for one limb might take between 20 to 30 minutes, but it can be longer if multiple nerves or limbs are tested.
Interpreting NCV Findings
Interpreting the findings of an NCV test involves analyzing several measurements, including conduction velocity, amplitude, and latency. Conduction velocity refers to the speed at which the electrical signal travels along the nerve. Amplitude indicates the strength of the electrical signal, reflecting the number of nerve fibers activated. Latency measures the time it takes for the nerve to respond to the electrical stimulus.
Normal NCV results vary depending on factors like age and the specific nerve tested, but a velocity between 50 and 60 meters per second is typical. Abnormal findings can point to different types of nerve damage. For instance, significantly slowed conduction velocity suggests demyelination, where the protective myelin sheath around the nerve is damaged. Reduced amplitude may indicate axonal damage, damage to the nerve fiber itself. An NCV test is frequently performed alongside an electromyography (EMG) test, which assesses muscle electrical activity, to provide a more comprehensive understanding of nerve and muscle health.