Median nerve evoked potential changes in an acute carpal tunnel syndrome model in Macaca mulatta.

We devised an acute, carpal tunnel syndrome (CTS) model in rhesus monkey, Macaca mulatta. This model was used to observe the relationship between increases in compartmental pressure and nerve function as reflected in the electrophysiologically generated, averaged evoked potential recorded from the skin superficial to the median nerve at the elbow. Two waves, an A beta and A delta were monitored. Increased carpal tunnel pressure produced a decrease in the A beta wave amplitude which was occasionally preceded by a slight elevation, but which eventually resulted in A beta wave abolition with pressures greater than or equal to 31 mm Hg. The A delta wave showed an initial increase in amplitude followed by a decline and abolition. Recovery rate from increased pressure for the A beta wave was directly proportional to the rate of abolition of that wave. The implications of these data are discussed in the context of CTS neuropathology and diagnosis.