Myokymic discharges: prompt cessation following nerve root decompression during spine surgery

In surgical cases during which spine nerve roots are at risk, we have found it useful to monitor EMG from the muscles supplied by those roots. Mechanical irritation of a root results in muscle activity, whose amplified signals can be broadcast over a loudspeaker, providing immediate feedback to the surgeon that the root is being irritated. We report here on a patient undergoing spinal canal decompression and fusion following a burst fracture of the L5 vertebral body sustained five days previously. EMG was continuously monitored from the tibialis anterior (TA) and medial gastrocnemius (MG) muscle groups bilaterally. During the period leading up to decompression, myokymic discharges from the left TA muscle were observed, whereas the other 3 muscles monitored did not show such activity. These semi-rhythmic and repetitive discharges from the left TA ceased immediately following surgical removal of a bone fragment compressing the left L5 nerve root. This indicates that the site of axonal irritation was the nerve root, and that myokymic discharges secondary to acute axonal compression can cease immediately upon nerve root decompression.