Polyphasic Potential
An EMG motor unit potential with five or more phases, often indicating muscle fiber dropout or temporal dispersion within motor units.
Full Definition
A polyphasic potential is an electromyographic motor unit potential characterized by five or more phases, defined as the number of baseline crossings plus one. Normal motor unit potentials are typically triphasic or tetraphasic, while polyphasic potentials suggest abnormal temporal dispersion of muscle fiber action potentials within a motor unit. This can result from various pathological processes including reinnervation, muscle fiber dropout, or conduction velocity differences among muscle fibers. Increased polyphasia is a sensitive but nonspecific indicator of neuromuscular pathology and may be seen in both neurogenic and myogenic disorders.
Usage
Usage note: Hyphenate when used as a compound modifier.
In Context
- "Increased polyphasic potentials were noted throughout the muscle." — EMG report
- "The percentage of polyphasic potentials exceeded normal limits." — Quantitative EMG analysis