An experimental study of spinal cord evoked potentials and histologic changes following spinal cord heating

To study the safety of hyperthermia cancer treatment, canine spinal cords were heated with radio waves to between 43 C and 47 C for 30 minutes. Spinal cord evoked potentials (SCEP) studied by epidural recording after epidural stimulation showed shortened latency and unchanged amplitude at 44 C or below. At 45 C or above, reduction of amplitude combined with shortened latency was observed, a phenomenon that has not hitherto been reported. After heating to 45 C, SCEP recovered with the reduction of temperature, but histologic examinations showed pigment exudation, vacuolation, and hemorrhage. These results suggest that tolerable spinal cord temperature should not exceed about 44 C.