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Somatosensory evoked potential (SEP) studies were performed in 14 patients with peripheral vascular disease who received epidural spinal cord stimulation (SCS) for chronic pain relief of the lower limbs. Signals were amplified and filtered between 20-2000 Hz and 200-2000 Hz to better identify activities in the high frequency range. In 7 patients bit-colour maps were also computed. In all the patients a homogeneous short-latency scalp evoked potential with a prevalent diphasic shape (P1-N1) was recorded. In all our scalp records, even with the wide bandpass, small short-latency positive deflections were observed on the descending front of the first major positive wave and they were better defined as a series of up to 6 wavelets, preceding the major negative scalp wave in the tracings filtered through the narrow bandpass. They appeared in an interval ranging from 5.5 to 15.6 msec. Bit-colour maps showed consistent positive fields, with a maximum at the vertex, starting mainly at about 5.5 msec; in 3 patients, a prominent positivity between 8.5 and 10.5 msec was recorded followed by smaller components preceding the major positive-negative (P1-N1) complex. More synchronous volleys during direct SCS produced clear short-latency SEPs. Although they were of larger amplitude, we regarded them as corresponding to those described by previous authors obtained by stimulation of nerves of the lower limbs, and probably arising from subcortical structures.

The median sensory nerve conduction between ring finger and wrist is a suitable parameter for early detection of carpal tunnel syndrome (CTS), although shorter segments of median nerve have also been proposed for the same goal. In order to assess the relative diagnostic value of the sensory nerve conduction velocity (SNCV) of the third palmar branch versus the SNCV of the second palmar branch, generally performed until now, we studied 62 patients with typical signs and symptoms of CTS. The following parameters were evaluated by surface recording: orthodromic SNCVs in digit-wrist segments for median (index = M2, third = M3 and ring = M4 fingers), ulnar (fourth = U4 finger) and radial (thumb = R1) nerves; SNCVs in palm-wrist segments by surface bipolar stimulation at each metacarpo-phalangeal interspace (second = P2 and third = P3 for the median nerve and fourth = P4 for the ulnar nerve); and distal motor latencies of the median and ulnar nerves. No responses at the wrist were recorded in 22.6% of patients after digital stimulation of M4, whereas the SNCV of P3, the palmar nerve branch arising from digital nerves of the medial side of M3 and the lateral side of M4, was measurable in 93.5% of patients. As significantly expressed (P < 0.001) by the increased ratio of the mean values of P2 and P3 in CTS patients, the SNCV of P3 decreased more frequently and to a greater extent than the SNCV of P2.