Clinical utility of surface EMG: report of the therapeutics and technology assessment subcommittee of the American Academy of Neurology.

Abstract

This report reviews the clinical uses of surface electromyography (SEMG) as a diagnostic tool for neurologic disorders. SEMG is assessed with regard to the evaluation of patients with neuromuscular diseases, low back pain, and disorders of motor control. This broadens the scope of a previous assessment of SEMG in neurologic practice by the American Association of Electrodiagnostic Medicine1 in which its utility was examined with regard to neuromuscular diseases only. Needle electromyographic evaluation (NEMG), in combination with nerve conduction studies, is the gold standard methodology for assessing the neurophysiologic characteristics of neuromuscular diseases. Moreover, fine-wire EMG (FWEMG) often has been used in the evaluation of gait disorders, kinesiologic studies, and research and is also considered a standard. Nevertheless, NEMG and FWEMG are both invasive and painful, and this limits their use when activity from several muscles needs to be monitored simultaneously. SEMG is a technique to measure muscle activity noninvasively using surface electrodes placed on the skin overlying the muscle. SEMG differs from NEMG and FWEMG with respect to technical requirements and electrical properties. Unlike NEMG, SEMG electrodes record from a wide area of muscle territory, have a relatively narrow frequency band (range, 20 to 500 Hz), have low-signal resolution, and are highly susceptible to movement artifact. SEMG electrodes typically are approximately 10 mm in diameter and usually are passive (i.e., they are simple conductive surfaces requiring low skin resistance). They can, however, be active, incorporating preamplifier electronics that lessen the need for low skin resistance and improve the signal-to-noise ratio. SEMG can record both voluntary and involuntary muscle activity in addition to externally stimulated muscle action potentials such as motor evoked potentials after central or peripheral nerve stimulation.2 SEMG has also been used in several non-neurologic settings such as obstetric monitoring and animal research, but these potential …