Incremental Response
An increase in compound motor action potential amplitude with repetitive nerve stimulation at high frequencies. Characteristic finding in presynaptic neuromuscular junction disorders.
Full Definition
An incremental response refers to a progressive increase in the amplitude and area of the compound motor action potential (CMAP) during high-frequency repetitive nerve stimulation, typically at rates of 20-50 Hz. This finding is characteristic of presynaptic neuromuscular junction disorders, most notably Lambert-Eaton myasthenic syndrome and botulism. The increment occurs because high-frequency stimulation increases calcium influx into the presynaptic terminal, enhancing acetylcholine release. An increment of greater than 100% from baseline is considered significant. This response pattern is opposite to the decremental response seen in postsynaptic disorders like myasthenia gravis.
Usage
Usage note: Always specify the percentage increase when documenting incremental responses.
In Context
- "High-frequency stimulation revealed a 200% incremental response, supporting the diagnosis of Lambert-Eaton syndrome." — Repetitive stimulation study
- "The incremental response was most pronounced in proximal muscles." — Electrodiagnostic evaluation