How do fasciculations fibrillations and positive sharp waves differ on needle EMG recording?
A fasciculation potential is an involuntary firing of an entire motor unit, that is, single motor neuron and all its innervated muscle fibers. This is seen as a large electrical spike on needle EMG recording of a relaxed muscle. It is sometimes clinically visible in the patient as a brief, irregular twitch of the muscle. This can often be seen in normal individuals; however, if in excess, it may be a sign of a motor nerve or motor neuron disorder.
A fibrillation potential is an involuntary contraction of a single muscle fiber that usually indicates denervation or muscle damage. Unlike a fasciculation, a fibrillation usually does not cause clinically visible muscle movement.
Positive sharp wave potentials are similar to fibrillation potentials in that they represent abnormal muscle fiber firing from nerve or muscle damage. They are identified by their initial positive deflection from the baseline as opposed to the initial negative deflection of a fibrillation potential.