Katsumi Yamashiro

Gamma Knife Thalamotomy for Parkinson Disease and Essential Tremor: A Prospective Multicenter Study

BACKGROUND No prospective study of gamma knife thalamotomy for intractable tremor has previously been reported. OBJECTIVE To clarify the safety and optimally effective conditions for performing unilateral gamma knife (GK) thalamotomy for tremors of Parkinson disease (PD) and essential tremor (ET), a systematic postirradiation 24-month follow-up study was conducted at 6 institutions. We present the results of this multicenter collaborative trial. METHODS In total, 72 patients (PD characterized by tremor, n = 59; ET, n = 13) were registered at 6 Japanese institutions. Following our selective thalamotomy procedure, the lateral part of the ventralis intermedius nucleus, 45% of the thalamic length from the anterior tip, was selected as the GK isocenter. A single 130-Gy shot was applied using a 4-mm collimator. Evaluation included neurological examination, magnetic resonance imaging and/or computerized tomography, the unified Parkinsons disease rating scale (UPDRS), electromyography, medication change, and video observations. RESULTS Final clinical effects were favorable. Of 53 patients who completed 24 months of follow-up, 43 were evaluated as having excellent or good results (81.1%). UPDRS scores showed tremor improvement (parts II and III). Thalamic lesion size fluctuated but converged to either an almost spherical shape (65.6%), a sphere with streaking (23.4%), or an extended high-signal zone (10.9%). No permanent clinical complications were observed. CONCLUSION GK thalamotomy is an alternative treatment for intractable tremors of PD as well as for ET. Less invasive intervention may be beneficial to patients.

Stereotactic Thalamotomy for Dystonie Patients

A total of 54 patients (22 females and 32 males) with dystonia underwent thalamotomy. These patients consisted of 25 dystonia musculorum deformans (DMD) and 29 secondary dystonia cases. All of the patients were analyzed prospectively. Preoperative and postoperative symptoms were compared and grade. The target areas of thalamotomy were the ventral intermediate (Vim) and posterior ventral oral (Vop) nuclei. 59% of the patients showed more than 25% improvement, 23% were slightly improved cases (less than 25%), and 16% showed no change or their symptoms had worsened.

Thalamotomy for Parkinson’s Disease: Microelectrode Technique

Surgery is the most effective means for treating disabling tremor in patients with Parkinson’s disease. An appropriately placed stereotactic lesion relieves tremor permanently and eliminates or greatly reduces rigidity on the opposite side of the body. Whether bilateral surgery can arrest the progress of the disease is a controversial issue [38, 47].

Neurones with Epileptiform Discharge in the Central Nervous System and Chronic Pain

Epileptiform discharge was recorded from neurons in the thalamic nuclei of chronic pain patients during stereotactic surgery. Hyperactive neurons showed regular firing of 3-5 trains of epileptic-like group discharges with a frequency of 4 to 5 Hz. As described by Lombard et al. (1979), we operated on the dorsal root unilaterally, sectioning C5 to Thl in male Wistar rats. One to three months after the operation, hyperactive neurons were examined in the contra-lateral thalamic nuclei (VP, zona incerta), and lemniscus medialis. The firing patterns and distribution of hyperactive neurons in these animals was very similar to those of humans. The hyperactive neuron was unaffected by electrical stimulation of the nucleus raphe dorsalis (NRD) and locus ceruleus (LC). Administration of phenytoin and diazepam reduced the firing. However, no effect was seen with valproic acid. During spreading depression of the sensorimotor cortex, a remarkable reduction was seen on the firing of thalamic hyperactive neurons. This suggested that hyperactive neurons of the thalamic nuclei received facilitory effects from the sensorimotor cortex with little influence from adrenergic or serotoenergic systems.

Origin of the initial negative potential (N15) recorded on the skull by superficial radial nerve stimulation in the cat

The origin of the initial prominent negative potential with a latency of about 15 msec (N15), recorded on the skull by superficial radial nerve stimulation was studied in the cat, and the following results were obtained. In the direct recording from the cortex, SEPs were elicited from the SI and SII areas, as well as the lateral gyrus and anterior suprasylvian gyrus. Among various wave forms recognized in the SI area, diphasic positive-negative (P-N) potential obtained from the postero-lateral part was most distinct, representing the primary evoked potential. Responses recorded on the dura and those directly on the cortex showed similar wave patterns over many sites. Although different forms of evoked potentials were recorded extensively over the skull, the most prominent negative potential was elicited at the site corresponding to the postero-lateral part of the SI area. The latency of this potential was approximately in agreement with that of the negative component of the P-N potential recorded on the cortex. Based on the intracortical laminar analysis of P-N potential, the positive component of this potential was assumed to reflect the activity of cells in the deeper layer of the cortex. The negative component, on the other hand, might represent activities of apical dendrites of the cortex. From the result of functional elimination of the cortex, however, this positive component was thought to contain potentials from far field neural structures. N15 recorded on the skull completely disappeared during cortical spreading depression.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes of somatosensory evoked potential accompanying ischaemia and hypoxia in cats

Changes of evoked potential accompanying haemorrhagic hypotension and hypoxia were investigated on cats to evaluate the usefulness of SEP as a monitor in an intensive care unit (ICU), and the following results were obtained. Positive-negative diphasic potential was elicited at posterior sigmoid gyrus(PSG) by contralateral superficial radial nerve stimulation. This potential was recorded at the restricted area of the posterior border of PSG and regarded as primary somatosensory evoked potential. In the initial stage of haemorrhagic hypotension, both positive and negative components of SEP occasionally increased in amplitude. In profound hypotension in which CBF fell to less than the critical level of 30 ml 100 g-1 min-1, the latency was retarded and the amplitude was decreased. At CBE less than 10 ml 100 g-1 min-1, SEP disappeared. Within the range of CBF between 10 and 30 ml 100 g-1 min, a close correlation was noted between CBF and SEP amplitude. Transient increase of SEP amplitude was also observed during hypoxia induced by inhalation of nitrogen gas. (3) In normal state SEP was decreased in amplitude by conditioning stimulation of the nucleus lateralis posterior (LP nucleus) of the thalamus. This might be explained by the fact that intracortical inhibitory interneurons were activated by stimulation of LP nucleus. After haemorrhagic hypotension and hypoxia, however, the inhibitory effect on SEP elicited by LP nucleus stimulation attenuated or disappeared. Because of the initial impairment of the inhibitory interneurons by ischaemia and hypoxia, the amplitude of SEP might increase transiently. In conclusion, the authors thought that SEP might be less useful than EEG in ICU, because of its insensible change to hypoxia and ischaemia.

Evoked potentials from the human thalamus: correlation with microstimulation and single unit recording.

During stereotactic surgery, intrathalamic single unit recordings and summated evoked potentials (Th-SEP), evoked by percutaneous electrical median nerve stimulation and intrathalamic microstimulation, were done using the same microelectrode at the same site. Potentials evoked by natural and electrical stimulation were compared. The format of Th-SEP varied in anteroposterior, mediolateral and dorsoventral directions in the ventrocaudal nucleus (Vc). The positive response peak latency was shortest from the caudal part of Vc and longest from the anterior part of Vc.

Effect of midbrain raphe nucleus stimulation on somatosensory evoked potential in cat

Experiments were carried out to clarify the effect of serotonin [5-hydroxytryptamine (5-HT)] upon the somatosensory evoked potential (SEP) elicited by superficial radial nerve stimulation in cat, and the following results were obtained: (i) in untreated (control) animals, a significant reduction occurred in amplitude of the SEP in response to conditioning stimulation of the dorsal raphe nucleus in the midbrain, within 100 ms of the interval between conditioning and test stimuli; (ii) in 5-HT depleted animals prepared by intraperitoneal injection of p-chlorophenylalanine (PCPA), the amplitude of SEP significantly increased in comparison with that of nontreated animals. Conditioning stimulation of the raphe nucleus in 5-HT depleted animals failed to cause any remarkable change in the SEP; (iii) the diminuation of the SEP by raphe nucleus conditioning reappeared following intraventricular administration of a large dose of 5-HT (200 micrograms) in the PCPA-treated animals. These results have demonstrated that the serotonergic system with its cell bodies located in the raphe nucleus of the midbrain has the function of reducing the amplitude of the SEP, thus suggesting that it acts as a suppressive control on the excitability of the cortex to sensory input.

Microstimulation for Stereotactic Neurosurgery

840 microstimulations were done in 21 patients with movement disorders and chronic pain. Paresthesia was the most common response and occurred in 53.3% of cell responses, since the present study was performed mainly in the nucleus ventrocaudalis (Vc). Sensorimotor responses were noted in 8.3%, mainly from the Vc, but they were also noted from the nuclei intermedialis (Vim) and oralis posterior (Vop). Motor responses were noted in 3.6%, mainly from the Vim and Vop nuclei. Pain sensation was elicited in 3.8% and no response was seen in 22.6% of cells after stimulation.

Spasmodic Head Movements Produced by Destruction of Unilateral Ventromedial Tegmentum in Cats

In cats, unilateral electrolytic destruction in the dorsomedial parts of the ventral tegmental area (VTA) (Tsai) led to the appearance of torticollic rotatory head postures associated with a marked drop of the corresponding caudate serotonin. Results obtained from fluorescence histochemistry and brain dialysis also revealed that decrease in serotonin shared the leading role. However, since a chemical lesion produced by neurotoxic agents failed to induce such abnormal postures, concomitant interruption of nonaminergic fibers at VMT might also be the essential factor. Among them the interstitial nucleus (Cajal) and its descending tract were the most suspicious.