Burnaby Neurology

Before testing, we will make some measurements using a measuring tape. There may be small pen marks used as indicators on your skin. The skin will be cleaned with alcohol. It is important to try to avoid placing creamy solutions on the skin before coming, as this disrupts the signals. Stickers will be placed on the skin over nerves or muscles to receive the signals after stimulation (see above left).

A stimulator will be placed on nerves with stimulation starting small and gradually getting bigger until the right amount of stimulation is applied (see above right). These shocks are very brief, far less than a second, and can never be harmful. Although some people find these uncomfortable, most patients find these to be well tolerated.

Are there any risks with the NCS and EMG study?

Not really - there can be discomfort for some patients. If you are on a blood thinner, then some of the needle pokes may have minor bleeding or a chance to form a bruise. If you have a pacemaker, then we would not shock over that area, and shocks placed elsewhere never affect the pacemaker itself. Needles used are always sterile and never re-used, so there is no risk of obtaining any infection. Sometimes, patients can have discomfort after the needle tests lasting up to a few hours afterwards. There are no other side effects of the testing. You can always drive, walk and perform any task after this is done.

What are the tests done during the NCS study?

The tests performed can be divised as follows:

• Sensory NCS are performed by electrical stimulation of a peripheral nerve and recording from a purely sensory portion of the nerve, such as on a finger. These shocks are small, and may be felt like a rubber band stretched and hitting against the skin. You will also feel an electrical sensation travelling down the nerve usually. We measure the distance travelled with a measuring tape. On the computer screen (see above), you will see waveforms showing up that allow us to measure the speed and size of the responses. 

• Motor NCS are performed by electrical stimulation of a peripheral nerve and recording from a muscle supplied by this nerve. These shocks are larger than with sensory testing. You will also feel an electrical sensation travelling down the nerve usually, but you will also notice your muscles contracting, leading to movement that you will not be controlling. We measure the distance travelled with a measuring tape. On the computer screen (see above), you will see waveforms showing up that allow us to measure the speed and size of the responses given at multiple sites along the same nerve.

• F-wave studies is not really a reflex, per se. It is a signal that started in the nerve and travelled back to the spinal cord, and then came back again to the muscle supplied by the nerve. This allows us to measure the nerve signals at the more proximal parts of the nerves and within the neck or back where spinal nerves exist. You will feel these shocks the same as with the motor NCS studies performed.

• H-reflex studies are more like a reflex. This study uses shocks over a nerve that travel up to the spinal cord before returning to the muscle supplied by the nerve. This allows us again to measure the nerve signals at the more proximal parts of the nerves and within the neck or back where spinal nerves exist. You will feel these shocks as generally smaller than the motor NCS studies performed.

Is this test done for myasthenia gravis?

Yes, although differently. In myasthenia gravis (MG), muscle fibers become easily fatigued. When given multiple stimulations, muscles in MG do not respond as well as normal muscles. Thus, we will test using short sequences of rapid, regular electrical impulses, sometimes before and after exercising the motor unit. This will permit the fatiguability of the muscle to be measured. This is called a repetitive nerve stimulation test. In this test, we look for a finding called a repetitive decrement, indicating a neuromuscular junction problem that can occur in myasthenia gravis and related conditions.