EMG: decremental response of compound muscle action potential to repetitive nerve stimulation

What it means

A compound muscle action potential (CMAP) is a type of electromyography (EMG). CMAP refers to a group of almost simultaneous action potentials from several muscle fibers in the same area evoked by stimulation of the supplying motor nerve and are recorded as one multipeaked summated action potential. This abnormality refers to a greater than normal decrease in the amplitude during the course of the investigation.

The result of this test is abnormal if progressively fewer muscle fibers respond to nerve stimulation during a train of stimuli, thereby yielding a decrementing pattern in the CMAP.

Rare diseases that can present with this7

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: EMG: decrement at repetitive stimulation · EMG: decremental response of CMAP to repetitive nerve stimulation