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Yoichi Katayama, Chikashi Fukaya and Takamitsu Yamamoto

Object. The goal of this study was to identify the neurological characteristics of patients with poststroke pain who show a favorable response to motor cortex (MC) stimulation used to control their pain.

Methods. The neurological characteristics of 31 patients treated by MC stimulation were analyzed. In 15 patients (48%), excellent or good pain control (pain reduction > 60%) was achieved for follow-up periods of more than 2 years by using MC stimulation at intensities below the threshold for muscle contraction. Satisfactory pain control was achieved in 13 (73%) of 18 patients in whom motor weakness in the painful area was virtually absent or mild, but in only two (15%) of the 13 patients who demonstrated moderate or severe weakness in the painful area (p < 0.01). Muscle contraction was inducible in the painful area in 20 patients when stimulated at a higher intensity. No such muscle response was inducible in the remaining 11 patients, no matter how extensively the authors attempted to determine appropriate stimulation sites. Satisfactory pain control was achieved in 14 (70%) of the 20 patients in whom muscle contraction was inducible, but in only one (9%) of the 11 patients in whom muscle contraction was not inducible (p < 0.01). No significant relationship was observed between pain control and various sensory symptoms, including the presence of hypesthesia, spontaneous dysesthesia, hyperpathia, and allodynia, or the disappearance of the N20 component of the median nerve—evoked somatosensory scalp potential. No significant relationship existed between the effect of MC stimulation on the pain and stimulation-induced phenomena, including paresthesia, improvement in motor performance, and attenuation of involuntary movements.

Conclusions. These findings suggest that the pain control afforded by MC stimulation requires neuronal circuits that are maintained by the presence of intact corticospinal tract neurons originating from the MC. Preoperative evaluation of motor weakness of the painful area appears to be useful for predicting a favorable response to MC stimulation in the control of poststroke pain.

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Chikashi Fukaya, Yoichi Katayama, Masahiko Kasai, Jun Kurihara and Takamitsu Yamamoto

✓ Intraoperative monitoring techniques for protecting the integrity of the oculomotor nerves during skull base surgery have been reported by several investigators, all of which involved the use of electromyographic responses to extraocular muscles. However, these techniques have not yet become popular because of the complexity of the procedures. The authors report an extremely simple and far more reliable technique in which electrooculographic (EOG) monitoring is used. The oculomotor nerves were stimulated with a monopolar electrode during skull base exposure. The polarity of the EOG responses recorded with surface electrodes placed on the skin around the eyeball yielded precise information concerning the location and function of the oculomotor and abducent nerves. In addition, with the aid of continuous EOG monitoring that detected transient changes in the background waves, surgical procedures that might impinge on oculomotor nerve function could be avoided. The present technique has been used in eight patients with skull base tumors and with it, the authors have achieved excellent results.

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Yoshihiro Murata, Yoichi Katayama, Kaoru Sakatani, Chikashi Fukaya and Tsuneo Kano

Object. It has been reported that extracranial—intracranial (EC—IC) arterial bypass surgery can be useful in preventing stroke in patients with hemodynamic compromise. Little is yet known, however, regarding the extent to which the bypass contributes to maintaining adequate cerebral blood oxygenation (CBO) and its temporal changes following surgery. The authors evaluated bypass function repeatedly by using near-infrared spectroscopy (NIRS) after surgery.

Methods. The authors investigated 30 patients who had undergone EC—IC bypass surgery. Single-photon emission computerized tomography revealed a decrease in regional cerebral blood flow (rCBF) and a lowered rCBF response to acetazolamide. Changes in CBO were evaluated in the sensorimotor cortex during compression of the anastomosed superficial temporal artery (STA). When decreases in oxyhemoglobin (HbO2) and total hemoglobin (Hb) concentrations were observed, the bypass was considered to have maintained CBO in the sensorimotor cortex given that decreases in HbO2 and total Hb indicate cerebral ischemic changes. The bypass maintained CBO immediately after surgery in 36.7% of patients (Group I, 11 patients) and at some time after surgery, mostly within 1 year, in 43.3% of patients (Group II, 13 patients); however, it did not maintain it throughout the follow-up period in 20% of patients (Group III, six patients). Note that the preoperative rCBF in patients in Groups I and II was lower than that in patients in Group III (p < 0.004). In fact, the preoperative rCBF predicted whether a bypass would maintain CBO at a cutoff value of 24.5 to 25 ml/100 g/min. Among Groups I and II, 18 patients demonstrated an increase in deoxyhemoglobin during STA compression. The preoperative rCBF in these cases was lower than that in the six remaining patients (p < 0.006). Note that the preoperative rCBF predicted the postoperative deoxyhemoglobin response at a cutoff value of 22.2 to 24 ml/100 g/min.

Conclusions. The EC—IC bypass surgery can maintain CBO immediately after surgery or gradually within 1 year when the preoperative rCBF is below 24.5 to 25 ml/100 g/min. Furthermore, bypass flow plays a critical role in maintaining an adequate CBO when preoperative rCBF is below 22.2 to 24 ml/100 g/min.

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Takamitsu Yamamoto, Yoichi Katayama, Kazutaka Kobayashi, Hideki Oshima and Chikashi Fukaya

✓ Using a new perforator, the authors have developed a new dual-floor burr-hole method for use in deep brain stimulation therapy. The modification is called “dual-floor” because the usual 15-mm-diameter burr hole, which is located centrally and reaches the dura mater, is surrounded by a 4-mm-wide rim that is also planed downward by the new perforator to a depth of 4 mm. This dual-floor burr hole is adjusted to fit the burr-hole ring and cap that are are supplied by the electrode manufacturer. Such a method eliminates bulging of the scalp just over the burr-hole ring and cap. In addition, it is helpful for securing a tight fixation between the burr-hole ring and the skull.

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Chikashi Fukaya, Yoichi Katayama, Masahiko Kasai, Jun Kurihara, Sadahiro Maejima and Takamitsu Yamamoto

Object. Histopathological studies on spinal cord injury (SCI) have demonstrated time-dependent spread of tissue damage during the initial several hours postinjury. When the long tract within the spinal cord is stimulated, a large monophasic positivity occurs at the injury site. This type of potential, termed the killed-end evoked potential (KEEP), indicates that a nerve impulse approaches but does not pass beyond the injury site. The authors tested the hypothesis that the damage spread can be evaluated as a progressive shift of the KEEP on a real-time basis. The effect of high-dose methylprednisolone sodium succinate (MPSS) on the spread of tissue damage was also examined by this methodology.

Methods. The KEEP was recorded using an electrode array placed on the spinal cord at the T-10 level in cats. This electrode array consisted of multiple 0.2-mm-diameter electrodes, each separated by 0.5 mm. Spinal cord injury was induced using a vascular clip (65 g pinching pressure for 30 seconds). The midline posterior surface of the spinal cord was stimulated bipolarly at the C-7 level by applying a single pulse at supramaximal intensity. During the initial period of 6 hours postinjury, the localization of the largest KEEP shifted progressively up to 2.5 mm rostral from the injury site. The amplitude of the KEEP recorded at the injury site decreased to 55 to 70% and became slightly shortened in latency as the localization of the largest KEEP shifted rostrally. These findings imply that the injury site KEEP represents the volume-conducted potential of the largest KEEP at the site of the conduction block. It moved away from the injury site in association with the damage spread, and this was confirmed histopathologically. A decrease in amplitude of KEEP at the injury site appeared to be the most sensitive measure of the damage spread, because the amplitude of the volume-conducted KEEP is inversely proportional to the square of the distance between the recording site and site of conduction block. Administered immediately after SCI, MPSS clearly inhibited these events, especially within 30 minutes postinjury.

Conclusions. The KEEP enables sequential evaluation to be made of the time-dependent spread of tissue damage in SCI in the same animal. It is, therefore, useful for detecting the effect of therapeutic interventions and for determining the therapeutic time window. The efficiency of MPSS to inhibit the spread of damaged tissue appeared to be maximized when it was administered within the initial 30-minute period postinjury.

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Takamitsu Yamamoto, Yoichi Katayama, Chikashi Fukaya, Hideki Oshima, Masahiko Kasai and Kazutaka Kobayashi

✓ Reversibility and adaptability are preferred features of long-term therapeutic deep brain stimulation (DBS). In such therapy, a permanent stimulating electrode with four contact points is placed at the stimulation site and, generally speaking, bipolar stimulation is induced by various pairs of adjacent contact points on one electrode. The stimulation sites are thus all located along the trajectory of the implanted electrode. In a patient with unilateral severe essential tremor, the authors implanted two electrodes side by side and parallel to each other in the unilateral thalamic ventralis intermedius nucleus. Using these electrodes, the authors were able to deliver current flow not only along the electrode trajectory, but also between the two electrodes in a direction parallel to the anterior commissure—posterior commissure line. Although individual stimulations, delivered by each of the two electrodes using all parameters and all stimulation points, were unable to stop the patient's tremor completely without adverse effects, the new stimulation method, in which electrical currents passed between the two electrodes, effected complete abolition of the tremor without adverse effects. With the aid of this method, one can use two electrodes, implanted in parallel and side by side, to achieve maximum efficacy and to reduce adverse effects in some instances of DBS therapy.

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Yoichi Katayama, Masahiko Kasai, Hideki Oshima, Chikashi Fukaya, Takamitsu Yamamoto, Katsuhiko Ogawa and Tomohiko Mizutani

Object. A blinded evaluation of the effects of subthalamic nucleus (STN) stimulation was performed in levodopaintolerant patients with Parkinson disease (PD). These patients (Group I, seven patients) were moderately or severely disabled (Hoehn and Yahr Stages III–V during the off period), but were receiving only a small dose of medication (levodopa-equivalent dose [LED] 0–400 mg/day) because they suffered unbearable side effects. The results were analyzed in comparison with those obtained in patients with advanced PD (Group II, seven patients) who were severely disabled (Hoehn and Yahr Stages IV and V during the off period), but were treated with a large dose of medication (500–990 mg/day).

Methods. The patients were evaluated twice at 6 to 8 months after surgery. To determine the actual benefits afforded by STN stimulation to their overall daily activities, the patients were maintained on their medication regimen with optimal doses and schedules. Stimulation was turned off overnight for at least 12 hours. It was turned on in the morning (or remained turned off), and each patient's best and worst scores on the Unified Parkinson's Disease Rating Scale during waking daytime activity were recorded as on- and off-period scores, respectively. The order of assessment with respect to whether stimulation was occurring was determined randomly.

The STN stimulation markedly improved daily activity and total motor scores in Group I patients. The percentage time of immobility (Hoehn and Yahr Stages IV and V) became 0% in patients who were intermittently immobile while not receiving stimulation. Improvements were demonstrated in tremor, rigidity, akinesia, and gait subscores. The STN stimulation produced less marked but still noticeable improvements in the daily activity and total motor scores in Group II patients. The percentage time of immobility as well as the LED was reduced in patients who displayed intermittent immobility with pronounced motor fluctuations while not receiving stimulation. Improvements were demonstrated in tremor, rigidity, and dyskinesia subscores in these patients. In contrast, STN stimulation did not improve the overall daily activities at all in patients who had become unresponsive to a tolerable dose of levodopa and were continuously immobile, even though these patients' tremor and rigidity subscores were still improved by stimulation.

Conclusions. Consistent with earlier findings, the great benefit of STN stimulation in levodopa-intolerant patients is that STN stimulation can reduce the level of required levodopa medication. This suggests that STN stimulation could be a therapeutic option for patients with less-advanced PD by allowing levodopa medication to be maintained at as low a dose as possible, and to prevent adverse reactions to the continued use of large-dose levodopa.

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Takamitsu Yamamoto, Yoichi Katayama, Toshikazu Kano, Kazutaka Kobayashi, Hideki Oshima and Chikashi Fukaya

Object. The tremor-suppression effect resulting from long-term stimulation of the thalamic nucleus ventralis intermedius (Vim) and the nucleus ventralis oralis posterior (Vop) was examined in the treatment of parkinsonian, essential, and poststroke tremor.

Methods. After identifying the accurate anterior border of the nucleus ventrocaudalis (Vc), deep brain stimulation (DBS) electrodes with four contacts were inserted into the Vim—Vop region at an angle of between 40 and 50° from the horizontal plane of the anterior commissure—posterior commissure line. Two distal contacts were placed on the Vim side and two proximal contacts on the Vop side. The best sites of stimulation and parameters of bipolar stimulation were selected in each case and follow-up examinations were conducted for at least 2 years.

In all 15 cases of parkinsonian tremor (18 sides) and in 14 of 15 cases of essential tremor (24 of 25 sides), cathodal stimulation of the Vim side with anodal stimulation of the Vop side was determined to be the best choice to suppress the tremor. In poststroke tremor, however, six of 12 cases (six of 12 sides) were selected for cathodal stimulation of the Vop side with anodal stimulation of the Vim side. The average stimulation intensity 1 month after initiation of DBS was 1.61 V in cases of parkinsonian tremor, 1.99 V in cases of essential tremor, and 2.39 V in cases of poststroke tremor. A comparison of stimulation intensities required at 1 and 24 months after initiation of DBS revealed that the lowest effective stimulation intensity increased 24.2% in cases of parkinsonian tremor, 21% in cases of poststroke tremor, and 46.9% in cases of essential tremor. Suppression of tremor was achieved in all cases (42 cases, 55 sides) during a period of 2 years. Nevertheless, two cases of poststroke tremor required dual-lead stimulation at the unilateral Vim—Vop region from the start of DBS, and two cases of essential tremor and one case of poststroke tremor required a stimulation intensity that was high enough to evoke unpleasant paresthesia and slight motor contraction during the follow-up period.

Conclusions. Effective stimulation sites and stimulation intensities differ in different kinds of tremor; Vim and Vop stimulation is necessary in many cases. Interactions of the Vim and Vop under the control of interconnected areas of the motor circuitry may play an important role in both the development and DBS-induced suppression of tremor.