Misao Tomita

Management of intractable pain with percutaneous epidural spinal cord stimulation : differences in pain-relieving effects among diseases and sites of pain

This study is a survey of the overall clinical results achieved with our pain treatment method, percutaneous epidural low-frequency (1.6-8.0 Hz) spinal cord stimulation. It examines the relationship between the effectiveness of epidural spinal cord stimulation (ESCS) and diseases or sites of pain. Continuous indwelling of the catheter electrodes in the posterior epidural space ranged from 3 to 67 days, and the duration of percutaneous ESCS varied from less than 1 wk to more than 1 yr. Complete pain relief (100%) was achieved during stimulation in 11.5% of the patients (52 of 454). Complete (100%) to partial (more than 30%) pain relief occurred in 71.1% of the patients. In six (1.3%) patients pain was aggravated by stimulation. Analgesics and/or sedatives were discontinued completely after treatment in 52 patients (11.5%) and reduced in 263 patients (57.9%). The number of patients who rated pain relief better than 50% was significantly more in carcinoma/sarcoma and causalgia (P < 0.001), and significantly less in postherpetic neuralgia and thromboangitis obliterans/arterial sclerosis obliterans (P < 0.001) than the average in all diseases. There was a significantly high responsiveness to ESCS in female patients in comparison to male patients (P < 0.05). Pain in the head/face, neck/upper extremities, and trunk responded more to ESCS than pain in the lower extremities. Alleviation of pain by ESCS was lower when the verbal pain score was high. There were no major complications in percutaneous ESCS. Thus, we have demonstrated that pain-alleviating effects of ESCS varies significantly by disease and site of pain, and that this simple percutaneous method can be used for a relatively long period.

Diagnosis of Spinal Disease with Ultrafine Flexible Fiberscopes in Patients with Chronic Pain

Study Design. Spinal epidural and subarachnoid spaces were observed with the newly developed fine flexible fiberscopes in 55 patients with chronic pain. Objectives. To evaluate the fiberscopes as diagnostic tools for spinal canal disease. Summary of Background Data. Fine flexible fiberscopes make it possible to visualize the entire length of the spinal subarachnoid space without major complications, and they may be of value for the diagnosis of certain spinal canal diseases. Methods. The epidural and subarachnoid spaces were accessed by fine flexible fiberscopes (Purely Fine [PF] types) in the initial 45 patients and by those equipped with a tip-steering function and a working channel (Medical Science [MS] types) in the later 10 patients, respectively. The procedures were based on those of continuous epidural or subarachnoid block. Results. Normal and abnormal subarachnoid spaces were clearly observed. When the MS types were used, the intended sites of the spinal structures could be more easily approached. In 12 patients, new diagnoses were made (chronic arachnoiditis 9, subarachnoid cyst 2, old subdural hematoma 1) that could not be found by magnetic resonance imaging or computed tomography. Additionally, chronic arachnoiditis was found in 2 patients with spinal trauma. Pathologic changes were confirmed by fiberscopic examination in 16 patients (arachnoiditis 11, spinal trauma 2, arteriovenous malformation 2, subarachnoid cyst 1). No pathologic changes could be detected in 27 patients with spinal canal stenosis, disc herniation, reflex sympathetic dystrophy, or posttraumatic pain syndrome. There were no significant differences in incidence of new diagnoses between the PF and MS types of fiberscopes. There were no major complications. There were 2 cases of light fever in the initial 10 patients and 7 cases of headache in the initial 14 patients. Only 4 cases of headache were observed in the subsequent 41 patients, in whom 20 mL of saline was injected into the epidural space. Conclusion. These fine flexible fiberscopes may provide new diagnostic and interventional tools for spinal canal diseases, provided skilled techniques are applied.

The placement of the epidural catheter at the predicted site by electrical stimulation test.

More accurate segmental and sagittal positioning of the epidural catheter tip is required for the success of continuous epidural analgesia, spinal cord monitoring, and percutaneous epidural spinal cord stimulation. We examined the usefulness of an electrical stimulation test for verifying the proper placement of the epidural catheter tip at the predicted site in the posterior epidural space by using a locally developed epidural catheter with electrodes at its tip. The test included the observation of segmental bilateral muscle twitches and the patient’s report of feeling in the region stimulated by moving the epidural catheter electrode back and forth and changing the direction of the bevel of the Tuohy needle. The success rate of midline placement at the required spinal segment was significantly more frequent (99%;P < 0.001) in the group (n = 289) receiving the electrical stimulation test compared with the group (n = 277) not receiving the test (success rate 57%). The results indicate the usefulness of this method. We concluded that the electrical stimulation test is effective for verifying the proper placement of the catheter electrode tip.

Effects of dorsal root entry zone lesion on spinal cord potentials evoked by segmental, ascending and descending volleys

SummaryThe spinal cord potentials (SCPs) were recorded from the dorsal root entry zone (DREZ) and posterior epidural space in patients before and after dorsal root entry zone lesion (DREZL) during general anaesthesia. The SCPs from the DREZ activated by segmental, ascending and descending volleys were basically the same in fundamental waveform as those recorded from the posterior epidural space. Segmentally activated slow negative (N1) wave, reflecting synchronized activities of dorsal horn neurones, and positive (P2) wave, thought to indicate primary afferent depolarization, were affected by DREZL in all 4 subjects tested, even by contralateral stimulation, suggesting that these components of the segmental SCPs in man partly reflect the activities of the contralateral dorsal horn. The spike-like potentials activated by ascending volleys were not affected by DREZL, while the subsequent slow components were decreased in the lesioned level. This may indicate that ascending spinal cord tracts are not affected by the operation, and suggests that the origin of the slow components by ascending volleys lies at least in part in the segmental dorsal horn. The slow negative and positive components, recorded at a remote segment from DREZL, in response to the descending volleys, were augmented after DREZL, suggesting that activation of ascending or descending inhibition through a feedback loop via the supraspinal structures might occur at least transiently following DREZL. All components of the SCPs activated by descending volleys were decreased or disappeared in recording from the lesioned level, as expected. Thus, intra-operative recording of the SCPs during DREZL might be beneficial for monitoring and studying human spinal cord function.

Spinal tracts producing slow components of spinal cord potentials evoked by descending volleys in man

Slow negative (N) and slow positive (P) waves are frequently produced in the posterior epidural space at the lumbosacral enlargement by epidural stimulation of the rostral part of human spinal cord. The production of these slow potentials are thought to be responsible for analgesia at the stimulated segment as well as below that level. In order to define the spinal tract which mediates these slow potentials, we stimulated directly or from the epidural space the dorsal, dorsolateral, lateral and ventral columns at the cervical or thoracic level, and epidurally recorded spinal cord potentials (des.SCPs) at the lumbosacral enlargement in 7 patients who underwent spine or spinal cord surgery. The des.SCPs recorded in the lumbosacral enlargement consisted of polyphasic spike potentials followed by slow N and P waves. At a near threshold level of stimulus intensity the slow N and P potentials were consistently elicited only by stimulation of the dorsal column. The slow waves were also produced by intense stimulation of other tracts, but remained significantly (P < 0.05 - P < 0.01) smaller than those evoked by dorsal column stimulation when compared at the same stimulus intensity. Moreover, the slow P wave could not be elicited even by intense stimulation (10 times the threshold strength for the initial spike potentials) of the ventral column. Thus, the results suggest that the slow N and P waves are mostly mediated by the antidromic impulses descending through the dorsal column.

Erb's point stimulation produces slow positive potentials in the human lumbar spinal cord.

Evoked spinal cord potentials (SCPs) were recorded from the posterior epidural space (PES) at the cervical and lumbrosacral enlargements in response to electrical stimulation of the brachial plexus at Erbs point in 17 chronic pain patients. Erbs point stimulation produced slow positive potentials (heterosegmental slow positive potentials, HSPs) in the PES at the lumbrosacral enlargement in all 13 subjects without spinal cord lesions but not in 4 subjects with spinal cord lesions. The HSP1 with a central peak latency of 21 +/- 2 ms (mean +/- SE) was recorded at the stimulus intensity up to two to three times the threshold strength (T) of the initially positive spike (P1) of the segmental SCP, which was simultaneously recorded from the PES at the cervical enlargement. At the stimulus intensity of more than 3T, another slow positive potential (HSP2) with central peak latency of 71 +/- 6 ms was recorded. These slow positive potentials (HSP1 and HSP2) might be produced by a feedback loop via supraspinal structures, presumably primary afferent depolarizations, in comparison to the HSPs of our previous studies in the rat. Slow negative potentials were sometimes noted before (5 of 13) and/or after (2 of 13) the HSP1. These slow negative potentials probably reflect the activities of dorsal horn neurons producing the HSP1 and HSP2, respectively, also elicited by a feedback loop via supraspinal structures.

Effects of Pentobarbital on Heterosegmentally Activated Dorsal Root Depolarization in the Rat Investigation by Sucrose-gap Technique In Vivo

Slow positive cord dorsum (P-) potentials activated by segmental stimulation are believed to reflect primary afferent depolarizations and have been shown to be augmented by barbiturates. However, there have been no data to confirm whether heterosegmentally activated P-potentials also represent primary afferent depolarizations and are similarly affected by barbiturates. We therefore tested whether heterosegmental P-potentials reflect primary afferent depolarizations and how these heterosegmental potentials are affected by barbiturates. Heterosegmentally activated dorsal root (DR) depolarizations (depolarizations evoked in DRs of lumbar segments in response to afferent volleys to cervical segments produced by electrical stimulation of the forepaw) and P-potentials were simultaneously recorded, adapting the sucrose-gap technique for recording DR depolarization in vivo in the rat. Forepaw (heterosegmental) stimulations produced a large depolarization in the DRs of L5-S1 as well as a slow P-potential in the lumbosacral enlargement. Transection of the spinal cord at the level of C1-C2 abolished both the P-potential and DR depolarization activated by heterosegmental stimulation as well as the second component of segmentally (hind-paw) activated P-potential. Bicuculline (100 micrograms/kg, intravenous) augmented the P-potential and DR depolarization produced by heterosegmental stimulation, but larger doses, 400-600 micrograms/kg, eventually suppressed these. However, the drug, in a dose-dependent manner, suppressed both the P-potential and DR depolarization produced by the segmental stimulation. Pentobarbital (10-40 mg/kg, intravenous) suppressed in a dose-dependent manner both the heterosegmental P-potential and heterosegmental DR depolarization and prolonged their peak latencies. By contrast, pentobarbital augmented and prolonged the segmental P-potential and segmental DR depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterosegmental SCPs (HSPs)

The bottom traces of Fig. 4.1A show the specimen records from the posterior epidural space (PES) of the lumbar enlargement in response to median nerve stimulation at the wrist in a wakeful subject. Any potentials were hardly noticeable in the lumbar enlargement. Thus, peripheral nerve stimulation at a distal site in the upper extremity can hardly evoke any potential change in the caudal segments of the spinal cord in a normal human. This, however, does not mean that peripheral nerve stimulation at a distal site in the upper extremity can hardly evoke any potential change in the caudal segments of the upper extremity or has no influence on spinal function in the lumbar enlargement. It is rather more likely that the electrical activity does exist but is barely demonstrated due to the temporal and spatial dispersion of the potential when the distal site of a peripheral nerve is stimulated. Therefore, it is predicted that when a more rostral site on the peripheral nerve is stimulated, a potential deflection could be more clearly demonstrated in the lumbosacral enlargement in humans, similar to that observed in the rat (Shimoji et al., 1986a,b,c).