Introduction

One of the fundamental principles of electrodiagnostic medicine is the assessment of the peripheral nervous system's ability to conduct an electrical impulse (Dumitru et al., 2002). Nerve conduction studies (NCs) and needle electromyography (EMG), are commonly referred to as electrodiagnostic or EMG studies. Electrodiagnostic studies play a crucial role in identifying disorders that affect the peripheral nerve, the dorsal root ganglia, the nerve root, or the anterior horn cell. Electrodiagnostic studies can also identify disturbances at the level of the neuromuscular junction and in the muscle. Additionally, EMG studies can provide useful information in disorders involving the upper motor neurons or disorders of volition as well as evaluating gait.

Thus, electrodiagnostic testing serves as an important diagnostic and prognostic tool when applied within the context of the clinical neurologic examination. A detailed, focused history and neurologic examination should serve as the template upon which one designs and performs the EMG study. Data acquired during the EMG study must always be interpreted within the clinical context because the same data may have very different interpretations depending on the clinical situation. An EMG study performed in isolation of the clinical context may provide little useful information.

Basic principles in EMG

The primary goals of the EMG study are to localize the lesion, characterize the underlying nerve pathophysiology, quantitate the severity of the lesion, and assess the temporal course of the disorder (Preston et al., 1998).