Computer-assisted DREZ microcoagulation: posttraumatic spinal deafferentation pain.

Our data demonstrate that approximately 23-29% of standard dorsal root entry zone (DREZ) microcoagulation procedures fail to relieve pain due to inadequate thermal lesions and that approximately 39% fail due to insufficient superior extent of lesions. The remaining failures are related to inadequate lesion placement, improper selection of patients, and, rarely, posttraumatic spinal deafferentation pain resulting from other non-DREZ mechanisms. Computer-assisted DREZ microcoagulation is a satisfactory procedure to treat intractable posttraumatic spinal deafferentation pain, brachial plexus avulsion pain, and lumbosacral nerve root avulsion pain. In all these conditions we have identified areas of abnormal focal hyperactivity in the DREZ area. Perhaps this procedure can be applied to other central pain conditions if, using this technique, abnormal focal hyperactivity is demonstrated to be present.

Intraoperative electrocochleography of endolymphatic hydrops surgery using clicks and tone bursts.

Seventy-seven ears of patients with Menière's disease (n = 69) and other ears with secondary endolymphatic hydrops (n = 8) underwent valved shunt surgery, and were monitored with intraoperative electrocochleography (ECoG) using clicks stimuli (n = 77), and both clicks and tone bursts (n = 37). Of the 41 ears in which the "baseline" measurement was > 35% summating potential to action potential (SP/AP) amplitude click ratio, 23 ears (56%) showed a significant ratio decrease (improvement). Twenty-six ears out of the 37 that were monitored by both clicks and tone bursts had abnormal absolute SP tone bursts amplitudes at "baseline" and 8 ears (31%) changed to normal at "closing". When tone burst ECoG information is combined with click stimuli, our basic understanding of click ECoG is enhanced and our ability to assess electrophysiologic changes intraoperatively is improved.

Intraoperative electrocochleographic monitoring of inner ear surgery for endolymphatic hydrops. A review of cases.

The purpose of this review of cases was to determine whether or not the SP/AP amplitude ratio changes during unidirectional inner ear valved shunt surgery for the decompression of the hydropic labyrinth in Meniere's disease. A series of 62 patients underwent shunt surgery over a 20 month period. In 43 cases (43 ears), ECoG responses were successfully recorded throughout the duration of surgery. A pair of two-tailed paired t-tests were computed for SP/AP amplitude ratios acquired during intraoperative ECoG monitoring at the baseline and closing stage of surgery. The first t-test compared the mean SP/AP amplitude ratios at baseline and closing for those cases in which the SP/AP amplitude ratio at baseline was abnormal (baseline > 35%). The t was significant, t(19) = 4.63, p < 0.01). The second t-test compared the mean SP/AP amplitude ratios at baseline and closing for those cases in which the SP/AP amplitude ratio at baseline was WNL (baseline < or = 35%). The t was insignificant, t(20) = 0.31, p > 0.05. Variations between baseline and closing measurements were categorized as either a reduction, no change (very stable over time), or an increase in the SP/AP amplitude ratio. A change in the SP/AP amplitude ratio from baseline to closing of > or = 7% (x = 2%, SD = 2%) was considered statistically significant. Overall (43 cases), 49% of the variations fell into the no change category, with 42% and 9% of the cases placed in the reduction and increase categories, respectively. Of the cases (22) in which the baseline measurement was outside the limits of normal, 64% showed a reduction, 32% showed no change, and 4% showed an increase in the SP/AP amplitude ratio at closing. Changes in the SP/AP amplitude were observed at various stages of the surgical procedure. Reductions were found at each of the five surgical steps identified, with the majority of the changes almost evenly divided between the stages of mastoid drilling and opening sac. Increases in the SP/AP amplitude ratio were found in four cases. The increases were observed during drilling of the mastoid bone in two cases and sac decompression and opening the sac in the remaining cases.

Effects of neocortical lesions on the P300 component of the auditory evoked response.

P300 event-related potentials were recorded in 10 subjects with neocortical lesions, and 10 control subjects, using a basic oddball paradigm. In separate tests, subjects discriminated rare and frequent tones that differed with respect to frequency, or discriminated the tones in a noise background. Subjects were required to count the number of rare stimuli that occurred during test runs. Recordings were obtained from vertex (Cz) sites referenced to linked earlobe electrodes. Control subjects exhibited P300s on all test runs. Decreasing stimulus differences relative to frequency, or adding background noise, produced significant increases in P300 latency plus decreases in amplitude. In contrast, two of the 10 lesion subjects failed to demonstrate P300 responses, although both subjects accurately counted the rare stimuli. With the remaining lesion subjects, absent or significantly delayed P300 responses occurred in 53 percent of the test runs, while accurate counts of the rare stimuli were maintained in all test runs. Absent or delayed P300s in the lesion group was not correlated with location or extent of the lesions. These results indicate that, while the P300 is susceptible to neocortical damage, it reflects cognitive processing other than simply discriminating differences between rare and frequent stimuli.