Abstract
We report two cases that showed giant waves in motor evoked potential (MEP) after carotid artery occlusion and discuss the significance of this phenomenon. During carotid endarterectomy (CEA), MEP and somatosensory evoked potential (SEP) are monitored to determine the use of intraluminal shunting in our department.
The first case was a 68-year-old male. An MEP giant wave appeared three minutes after carotid artery occlusion, while the amplitude of SEP decreased about 50%. After shunting, the MEP amplitude recovered and maintained recovery until the end of surgery. The SEP amplitude showed a decrease of up to about 10% even with shunting but recovered at the end of surgery. The second case was an 80-year-old male. An MEP giant wave appeared four minutes after carotid artery occlusion, while the amplitude of SEP decreased about 50%. After shunting, the MEP amplitude recovered and maintained recovery until the end of surgery. The SEP amplitude showed a decrease of up to about 70% but recovered at the end of surgery.
In early ischemia, excitability of pyramidal neurons increases because of cell depolarization due to calcium influx, and the transmission of inhibitory neurons is decreased. These changes cause an increase of the MEP amplitude. We were able to detect early ischemic changes by observing an MEP giant wave.
An MEP giant wave after carotid artery occlusion is a warning sign of ischemia even if such a waveform is recorded. Reperfusion should be achieved as soon as possible because MEP giant waves indicate ischemic intolerance.
