Blocking
Intermittent failure of neuromuscular transmission resulting in absent muscle fiber action potentials during single-fiber electromyography. Indicates severe neuromuscular junction dysfunction.
Full Definition
Blocking refers to the intermittent failure of action potential propagation across the neuromuscular junction, observed as the sudden disappearance of one component of a single-fiber potential pair during SFEMG recording. This phenomenon occurs when the safety factor for neuromuscular transmission is critically reduced, leading to intermittent conduction failure. Blocking is quantified as the percentage of attempted transmissions that fail to generate a muscle fiber action potential. Any blocking is considered abnormal and indicates significant neuromuscular junction pathology. Blocking percentage greater than 10% is highly suggestive of disorders like myasthenia gravis, Lambert-Eaton syndrome, or botulism. The presence of blocking often correlates with clinical weakness and functional impairment.
Usage
Usage note: Always report as a percentage when quantifying blocking in SFEMG studies.
In Context
- "Blocking was observed in 35% of fiber pairs, confirming severe neuromuscular transmission defect." — Single-fiber EMG report
- "The absence of blocking helped rule out significant neuromuscular junction pathology." — SFEMG interpretation