Nerves are like cables that carry electrical impulses or signals between your brain and the rest of your body. These impulses help you feel sensations and move your muscles. A nerve conduction study works by testing the transmission of these signals, especially the speed at which they travel and their “strength.”

The study involves wires (electrodes) taped to your skin in specific places along a nerve pathway. A provider stimulates the nerve with a mild electrical shock. As the electrical current travels down the nerve, the electrodes record the current and how fast it’s traveling.

The test involves two primary components:

• Stimulation: Electrodes are placed on the skin over the nerve to be tested. A mild electrical impulse is delivered to the nerve, causing the muscle it innervates to contract.
• Recording: A second electrode is placed along the path of the nerve or over the target muscle to record the time it takes for the electrical signal to travel between the two points. The speed (conduction velocity) and size (amplitude) of the response are analyzed.

If the provider stimulates a motor nerve, they measure the response of the muscle it controls. If they stimulate a sensory nerve, they record the response somewhere else along the nerve.

In healthy nerves, electrical signals can travel up to 120 miles per hour. If your nerve is damaged, the current will be slower and weaker. By stimulating the nerve at various places, the provider can determine the specific site of the nerve injury or issue.

• Conduction Velocity: This is the speed at which an electrical impulse travels along a nerve. Slowed conduction can indicate damage to the myelin sheath (the protective covering of nerves), as seen in conditions like demyelinating neuropathies.

• Amplitude: The size of the electrical response reflects the number of functioning nerve fibers. Reduced amplitude suggests axonal damage (damage to the nerve fibers themselves), commonly seen in axonal neuropathies.

• Motor NCS: Measures the ability of motor nerves to conduct electrical signals to muscles, causing them to contract. This test helps diagnose disorders affecting motor function, such as radiculopathies or motor neuron diseases.

• Sensory NCS: Assesses the ability of sensory nerves to transmit signals related to touch, pain, and temperature from the skin to the brain. Sensory NCS is useful for detecting conditions like carpal tunnel syndrome or peripheral neuropathy, which can cause numbness or tingling.

Nerve Conduction Studies are essential for diagnosing various peripheral nerve disorders, including:

• Carpal Tunnel Syndrome: Compression of the median nerve at the wrist causes pain, numbness, and muscle weakness in the hand. NCS can confirm the presence and severity of nerve compression.

• Ulnar Neuropathy: Compression or injury to the ulnar nerve, often at the elbow, leading to hand weakness and numbness in the ring and little fingers.

• Peripheral Neuropathies: Such as diabetic neuropathy, where nerve damage results from high blood sugar levels, leading to symptoms like numbness, tingling, and muscle weakness in the extremities.

• Guillain-Barré Syndrome (GBS): An acute inflammatory demyelinating polyneuropathy that affects the myelin sheath of peripheral nerves, causing rapid-onset muscle weakness. NCS helps identify slowed conduction velocity typical of GBS.

• Radiculopathy: Nerve root compression in the spine, often due to herniated discs or spinal stenosis, can cause pain, weakness, or numbness in the affected limb. NCS helps differentiate between nerve root and peripheral nerve damage.

• Brachial Plexopathy: Damage to the brachial plexus, the network of nerves supplying the arm and hand, often caused by trauma or stretching, can be diagnosed through NCS.

• Before you have a nerve conduction study, you should:
  Bathe or shower and wear comfortable, loose-fitting clothing.
• Avoid putting cream, lotion or perfume on your skin. Creams and lotions can affect the test’s accuracy.
• Tell the provider performing the study if you have a pacemaker or any other electrical medical device.

The process can vary for a nerve conduction study, depending on the reason for the test and which nerves the provider is assessing. But in general, you can expect the following during a nerve conduction study:

• You’ll sit or lie down for the test.
• A healthcare provider will stick electrodes to the surface of your skin above the nerves they’re assessing.
• They’ll attach different types of electrodes to the muscle or skin area that those nerves control.
• The provider will then deliver a small electrical impulse to your nerves to send a signal to the muscle it controls. You may feel a mild tingling feeling.
• They’ll record the time it takes for your muscle or skin to respond to the nerve signal.
• Then, they’ll repeat the same process in the next nerve until they’ve gathered enough information.

Providers usually perform an EMG test after the nerve conduction study.

Although the electrical stimulation may startle you initially, it shouldn’t be painful. The shock feels similar to a shock you experience from static electricity, or it may feel like a mild tingling. Most people can complete the test without issues.

A nerve conduction study can take anywhere from 15 minutes to an hour or more.

It depends on how many nerves your healthcare provider tests.