conduction block
Focal failure of nerve impulse transmission resulting in reduced CMAP amplitude with proximal versus distal stimulation.
Full Definition
Conduction block is a focal failure of action potential propagation along a nerve fiber, typically caused by focal demyelination or compression. It is diagnosed when proximal nerve stimulation produces a significantly reduced compound muscle action potential amplitude compared to distal stimulation, without corresponding prolongation of duration. A reduction greater than 20% (or 50% in some criteria) suggests definite conduction block. This finding is characteristic of acquired demyelinating neuropathies, focal nerve compressions, and some hereditary neuropathies.
Usage
Usage note: Specify anatomical location and percentage amplitude reduction when describing conduction block.
In Context
- "Conduction block across the elbow segment suggested ulnar neuropathy at the cubital tunnel." — Nerve conduction study
- "Multiple sites of conduction block were identified, supporting a diagnosis of multifocal motor neuropathy." — Electrodiagnostic interpretation