Introduction

In the previous review article, I discussed the fundamentals of nerve conduction studies, and here I hope to give an insight into the technique of electromyography (EMG). In reality, treating these as two separate topics is somewhat artificial; they give complementary information, and it would be very rare to perform EMG without first performing nerve conduction studies. Similarly, I not infrequently go back to check a couple of further nerves on the basis of what I find on EMG. Thus, the examination becomes a fluid (some might say balletic) process involving both techniques, as hypotheses as to the site or nature of a lesion are formed and refined.

EMG records the electrical activity arising within muscles. You can record this activity with surface electrodes, known as surface EMG. This samples a large region of the muscle, and while it gives a good indication of which muscle groups are active in for example tremor or dystonia, it gives little information as to the fine structure of those muscles. For this, you need needle EMG, which allows recording from within the muscle (figure 1). The rest of this review relates solely to needle EMG.