Introduction to Needle Electromyography

Abstract

The electrodiagnostic (EDX) examination is an extension of the clinical examination. When used correctly it defines the location, pathophysiology, severity, and chronicity of a wide array of neuromuscular disorders. It is comprised of two parts: nerve conduction studies (NCS) and needle electromyography (EMG). While both portions are performed differently and have individual advantages and disadvantages, together they provide complimentary information on the integrity of the peripheral nervous system (Table 4.1). The needle EMG is most likely to be tolerated and helpful when the examiner uses a gentle and informed approach, wisely selects muscles to examine in order of greatest yield, and understands the value and limitations of this technique.For the uninitiated, interpretation of the needle EMG is primarily visual, but the experienced EDX examiner understands that the needle EMG is equally, if not more dependent, on auditory recognition. As such, interpretation of the needle EMG is similar to learning not just a new skill but a new language. This introduction to the principles and performance of the needle EMG will address the following questions: •What do we measure with the needle EMG? •How do we perform these measurements? •What do the measurements mean? •How do different diseases affect these measurements? •How do these measurements correlate with motor NCS?