positive sharp wave
Spontaneous electrical discharge from denervated muscle fibers with characteristic initial positive deflection.
Full Definition
Positive sharp waves are spontaneous action potentials generated by denervated muscle fibers, characterized by an initial sharp positive deflection followed by a slow negative phase. These potentials typically have larger amplitude than fibrillation potentials and produce a characteristic firing pattern. Like fibrillation potentials, positive sharp waves indicate denervation but may appear earlier after nerve injury. They are commonly seen in various neuromuscular disorders including radiculopathies, neuropathies, and myopathies with membrane instability.
Usage
Usage note: May be abbreviated as PSW; always describe the initial positive deflection as the defining characteristic.
In Context
- "Positive sharp waves were present throughout the paralumbar muscles, suggesting L5 radiculopathy." — EMG interpretation
- "The combination of fibrillation potentials and positive sharp waves confirmed active denervation." — Electrodiagnostic report