The neuromuscular system includes all the muscles in the body and the nerves serving them. Neuromuscular disorders affect the nerves that control voluntary muscles and the nerves that communicate sensory information back to the brain.
What is an EMG?
An EMG is a test that will assess the function of the nerves and muscles in your child. It’s likely that the referral has been because your child is either weak all over or has some focal weakness, maybe restricted to one limb. The EMG is a very useful test to determine quite quickly if there are any problems with the nerves and muscles and guide further management more effectively. Without EMG it is quite possible to miss some treatable conditions completely or if not, delay their management. It’s therefore a very important help to your referring consultant.
What happens in EMG?
There are two parts to this test.The first is an assessment of the function of the nerves. This is performed by placing small sticky electrodes onto the surface of the skin and then using small electrical stimuli at a point along the nerve. For a sensory nerve you stimulate at one point and record a little way down the nerve (figure 1). This tests the function of the nerves which allow you to feel.
The nerves that allow you to move your muscles are tested in a similar way and in appearance almost the same as the test for the sensory nerve. The sticky electrodes are on the muscle this time and then stimulation of the nerve will produce a small jerk of the muscle. This is a little bit more uncomfortable than testing the sensory nerves.
After the nerves have been tested one moves on to an assessment of the muscles. This is done with a very thin wire, no thicker than an acupuncture needle, which is placed under the skin and into the muscle itself. It is inserted very quickly and is hidden in the palm of the examiner (figure 2). The child is asked to contract the muscle and the activity recorded. This produces a sound on the loudspeaker of the machine and for this reason we never talk about needles but rather a little microphone on a wire. The data is analysed later when the child has left.
Figure 2 In this staged demonstration of EMG in an older subject, A shows the needle in the palm of the examiner, B how it is placed in the muscle and C what the patient will see.
What is the experience like for your child?
The test is not painless and the child does feel discomfort. Nobody will pretend when talking to the child that it is not felt, as very quickly they will realise that this is not the case and will not trust you from that point on. Some children can be upset by the examination. In a study we made comparing our tests to blood tests, there was a wide variety of levels of discomfort, but a significant majority found it less uncomfortable than a blood test.
There have been many attempts to make it less uncomfortable. Some have used medication such as sedation or strong painkillers but it’s been found that with effective distraction a similar acceptability can be reached. We favour distraction and have been using this effectively for many years. It is very important to bring anything that the child enjoys such as video games, films on the iPad, etc. to allow the child to look at them during the process.
The child is the focus of the examination and all efforts are geared towards developing a rapport with the child (if old enough) by discussing things that they like. Although discussion on such unimportant matters may seem to take away from the importance of the examination, it’s under this smokescreen that one is able to do what is needed.
The examination is performed with the child on the lap of the parents or other adult until too old to do this. There is no restriction on the people who come into the examination room and it’s often very helpful to have grandparents and others to help distract the child.