Ham-Min Tseng

Network modulation by the subthalamic nucleus in the treatment of Parkinson's disease.

Deep brain stimulation of the subthalamic nucleus (STN DBS) has become an accepted tool for the treatment of Parkinsons disease (PD). Although the precise mechanism of action of this intervention is unknown, its effectiveness has been attributed to the modulation of pathological network activity. We examined this notion using positron emission tomography (PET) to quantify stimulation-induced changes in the expression of a PD-related covariance pattern (PDRP) of regional metabolism. These metabolic changes were also compared with those observed in a similar cohort of patients undergoing STN lesioning. We found that PDRP activity declined significantly (P < 0.02) with STN stimulation. The degree of network modulation with DBS did not differ from that measured following lesioning (P = 0.58). Statistical parametric mapping (SPM) revealed that metabolic reductions in the internal globus pallidus (GPi) and caudal midbrain were common to both STN interventions (P < 0.01), although declines in GPi were more pronounced with lesion. By contrast, elevations in posterior parietal metabolism were common to the two procedures, albeit more pronounced with stimulation. These findings indicate that suppression of abnormal network activity is a feature of both STN stimulation and lesioning. Nonetheless, these two interventions may differ metabolically at a regional level.

Metabolic changes following subthalamotomy for advanced Parkinson's disease.

We studied 6 advanced‐stage Parkinsons disease patients with [18F] fluorodeoxyglucose/positron emission tomography before and 3 months after unilateral ablation of the subthalamic nucleus performed with microelectrode mapping. Operative changes in glucose metabolism were assessed by comparing baseline and postoperative scans. We also quantified operative changes in the activity of an abnormal Parkinsons disease‐related metabolic network that we had identified in previous [18F] fluorodeoxyglucose/positron emission tomography studies. Following unilateral subthalamic nucleus ablation, a highly significant reduction in glucose utilization was present in the midbrain ipsilateral to the lesion site, most pronounced in the vicinity of the substantia nigra pars reticularis. Significant metabolic reductions were also present in the ipsilateral internal globus pallidus, ventral thalamus, and pons. Operative changes in Parkinsons disease network activity differed significantly for the lesioned and unlesioned hemispheres. In the lesioned hemisphere, network activity declined significantly following surgery, but was unaltered in the contralateral, unlesioned hemisphere. These results suggest that subthalamotomy reduces basal ganglia output through internal globus pallidus/substantia nigra pars reticularis and also influences downstream neural activity in the pons and ventral thalamus. This procedure also reduces the activity of abnormal Parkinsons disease‐related metabolic brain networks, suggesting a widespread modulation of motor circuitry.

Treatment of advanced Parkinson's disease by subthalamotomy: One‐year results

We studied effects on parkinsonian features at 6 and 12 months in 12 patients who underwent unilateral ablation of subthalamic nucleus (STN). Microelectrode mapping was used, and a lesion was created in the STN using thermal coagulation and confirmed with magnetic resonance imaging. At 6 months postoperatively, improvements were seen in several areas: 1) Unified Parkinsons Disease Rating Scales II and III (UPDRS II and III) scores, 30% in off period, 38% in on period; 2) Schwab and England Scale (S&E) score, 21%; and 3) on dyskinesia, 85%. Contralateral rigidity, bradykinesia, UPDRS II and III scores, and S&E scores remained improved at 12 months. Daily dosage of levodopa requirement was reduced by 42%. Axial motor features, gait, postural stability, off period tremor, and motor fluctuation improved at 6 and 12 months but showed a decline in benefits at 18 months. Complications include 3 cases of hemiballism, of whom 2 patients recovered spontaneously but 1 died from aspiration pneumonia. One patient had asymptomatic hematoma, and 2 suffered transient postural asymmetries. We conclude that unilateral subthalamotomy results in moderate improvement in all aspects of parkinsonian features, allows reduction in the dose of levodopa required, and ameliorates drug‐induced complications throughout 12‐month assessments.

Preoperative versus Postoperative Role of Vestibular‐Evoked Myogenic Potentials in Cerebellopontine Angle Tumor

Objective/Hypothesis Vestibular‐evoked myogenic potential (VEMP) examination was performed on patients with a cerebellopontine angle (CPA) tumor to evaluate its clinical role.

Postural asymmetries following unilateral subthalomotomy for advanced Parkinson's disease.

Two cases of postural asymmetries following unilateral stereotaxic subthalamotomy were observed with head and body tilting to the side contralateral to the STN lesion, which corrected itself completely or partially with levodopa treatment. After subsequent contralateral STN surgery, the postural asymmetry disappeared in both patients. Possible mechanism is discussed.

Clinical presentation of posterior fossa epidermoid cysts

The aim of this study was to investigate the audiovestibular deficits in those with posterior fossa epidermoid cyst including cerebellopontine angle in two patients and cerebellum in one patient. Prior to operation, all three patients showed bilateral gaze nystagmus. Audiometry revealed mild hearing loss in two patients, and caloric test displayed canal paresis in two patients. After operation, subsidence of gaze nystagmus and recovery of caloric responses were disclosed in all patients. Two patients had both hearing and vestibular evoked myogenic potential (VEMP) results recovered to normal. In contrast, the only one who underwent craniotomy twice displayed bilateral mild hearing loss and delayed VEMPs, possibly due to operation sequela. Hence, bilateral gaze nystagmus may present as an initial sign for posterior fossa epidermoid cyst. Audiovestibular deficits in cases of epidermoid cyst are attributable to compression neuropathy, which may resolve and return to normal responses after surgery.

Gait freezing and falling related to subthalamic stimulation in patients with a previous pallidotomy.

We have encountered similar difficulties in our patients who have had previous pallidotomy followed by subthalamus (STN) surgery as reported in a recent letter to the Editor by Dr. Merello ( Marcelo Merello, MD, PhD. “Subthalamic Stimulation Contralateral to a Previous Pallidotomy: An Erroneous Indication?”Movement Disorders , 1999:14(3);536). Morello’s case was frustrated by the management of dyskinesia and gait freezing secondary to the adjustment of medications. In contrast, our cases did not have a problem with dyskinesia but were troubled by axial symptoms such as falling and gait freezing. As there have been more than one thousand cases of pallidotomy reported in the literature, 1 we suspect more of these patients will eventually have unilateral STN surgery and experience similar problems. We report two cases with previous pallidotomy: one who then underwent unilateral STN implant surgery and the other, bilateral implants of deep brain stimulation (DBS) electrodes. Patient one is a 56-year-old right-handed woman with a 17year history of Parkinson’s disease (PD). Three years ago she had a left pallidotomy and left thalamotomy performed simultaneously in another hospital. After surgery, the right-sided rigidity and painful dystonia improved. She could walk unassisted with medication of Levodopa 200mg, Benserazide HCL 50mg (Madopar 250mg) four times per day and Pergolide Mesylate 0.5mg four times per day. She began to have motor complications with “wearing off” phenomenon, motor fluctuations, and freezing two years ago. Response fluctuation in the afternoon was severe enough that she was afraid to leave her house. At the time of STN surgery in June 1999, she demonstrated a Hoehn & Yahr stage IV (off) and stage III (on). The Unified Parkinson’s Disease Rating Scale (UPDRS) motor section was 50 and 17 (off and on, respectively); Schwab and England activities of daily living (ADLs) were 40%. There was moderate asymmetry in bradykinesia and rigidity, which was worse on the left side. It was decided that right STN surgery would be appropriate. DBS-3389 electrode (Medtronic, Minneapolis) was implanted within the STN under MRI localization and microelectrode recording technique without complications. She was discharged with the same amount of medication because her subthalamotomy effects were minimal. The stimulator was turned on one week after surgery. In the “on” state, at 3.2 volts, 60ms and 130 Hz, she clearly exhibited left hemiballism, which disappeared when the voltage was reduced to 2.8 volts. Stimulation parameters initially were set at monopolar 130 Hz, 60msec pulse width and voltage were increased gradually. At 2.0 volts, there was significant improvement in axial symptoms, such as rising from a chair, in addition to improvements in rigidity and bradykinesia of contralateral limb. However, the distressing and disabling problem of falling and gait freezing developed. She would fall unexpectedly while walking. She described it as if both feet were sticking to the ground while her upper body was still moving forward. When she was reaching out to get something, her feet wouldn’t move, resulting in a fall. She felt so unsteady as she was walking that she moved cautiously and slower than before. She fell 5–6 times per day when the stimulator was set above 2.0 volts. We feel that her falling was due half to freezing and half to posture imbalance. A postoperative MRI showed the DBS electrode was in the right subthalamus with point zero at the upper margin of the substantia nigra. Many attempts were made to adjust dosages of levodopa and the parameters of the stimulator without success. After three months of unsuccessful trials, the stimulator was switched off and her falling problem stopped. Although there was an improvement in falling, she could not turn in bed at night and she could not get out of bed by herself with the stimulator off. When the stimulator was set on 24 hours per day at 1.8 volts, pulse width 60 ms and 130 Hz, her problem of getting out of bed resolved, although she continued to fall once per two weeks. STN stimulation did not help the motor fluctuation or wearing off phenomenon that bought her to surgery in the first place. Any attempt to increase voltage above 2.0 volts resulted in frequent falling and gait freezing up to 5–6 times per day. On March 3, 2000, subthalamotomy of the left side was carried out using a radiofrequency thermal coagulation probe (Radionic Inc., Burlington, MA) without complication. Postoperatively, her falling and gait freezing stopped with right DBS set at 2.2 volts, 130 Hz and 60 msec. There is no more motor fluctuation or wearing off phenomenon while on Mardopar half table (125mg) and Pergolide Mesylate 0.5mg four times per day. Her ADLs are 90% and UPDRS motor section is 20 and 7 (off and on, respectively). The second case is that of a 63-year-old right-handed woman with a 10-year history of PD. In 1996, motor fluctuation, tremor, and dyskinesia were disabling enough that she had a left pallidotomy and left thalamotomy performed simultaneously in another hospital. After surgery, her dyskinesia improved but motor fluctuation and tremor did not. While taking L-dopa 200 mg, Benserazide HCL 50mg (Madopar 250mg) and Lisuride Maleate 0.2mg four times per day she could walk with assistance during the “on” state. However, the total “on” period lasted only one hour during a typical 12-hour day. She was totally incapacitated the rest of time, dependent upon a caretaker. At the time of STN surgery in June 1999, she presented with a Hoehn & Yahr stage V (off) and stage IV (on). Unified Parkinson’s Disease Rating Scale (UPDRS) motor section was 68 and 39 (off and on, respectively) and activities of daily living (ADLs) were 20%. Her [ F]Fluorodeoxyglucose (FDG) Positron Emission Tomographic (PET) scan showed hyperactive basal ganglia bilaterally, greater on the right side. There was moderate rigidity in the left upper and lower extremities while no rigidity was detected in the right side. A severe resting tremor of 4–5cps was present in the right upper extremity as well as a moderate tremor of the jaw and the left upper extremity. Because of severe gait disorder and axial rigidity withMovement Disorders Vol. 16, No. 2, 2001, pp. 376–377

A Proposed Method to Comprehensively Define Outcomes in Acoustic Tumor Patients Undergoing CyberKnife Management

Background: Vestibular assessment in patients with acoustic tumor (so-called vestibular schwannoma, VS) via ocular vestibular-evoked myogenic potential (oVEMP) and cervical VEMP (cVEMP) tests are not often discussed in the neurosurgical literature. Objectives: This study conducted physiological and morphological assessments for VS patients before and after CyberKnife radiosurgery. Methods: Twenty patients with unilateral VS underwent a battery of tests comprising facial nerve function test, audiometry, and caloric, oVEMP and cVEMP tests before and 2 years after CyberKnife treatment at a mean dosage of 18 Gy in 3 fractions. Results: The abnormal percentages of caloric, oVEMP and cVEMP tests did not significantly differ before and after Cyberknife treatment, indicating that preservation of the superior and inferior vestibular nerves can be achieved after radiosurgery. Median tumor volumes, 1.49 cm3 before treatment versus 0.97 cm3 at 2 years after treatment, differed significantly. Conclusions: The use of oVEMP and cVEMP tests in VS patients before stereotactic radiosurgery may help to evaluate the tumor origin from the superior or inferior vestibular nerve. It takes a short time and costs less, and it would be practical to make this a routine examination in VS patients having stereotactic radiosurgery.

Extradural dumbbell schwannoma of the hypoglossal nerve: a case report with review of the literature.

BACKGROUND Dumbbell-shaped schwannomas of the hypoglossal nerve are very rare. This report concerns a case with an extradural, dumbbell-shaped hypoglossal schwannoma extending both intra- and extracranially. CASE DESCRIPTION A 25-year-old woman presented with a right hypoglossal palsy. Imaging revealed a dumbbell-shaped tumor with considerable compression and medial displacement of the medulla oblongata, diagnosed as a hypoglossal schwannoma. The tumor mass extended extracranially to the parapharyngeal space through the enlarged hypoglossal canal. The tumor was partially excised by a right far-lateral suboccipital approach and the tumor was found to be predominantly extradural with minimal intradural extension. A histopathologic diagnosis of schwannoma was made. CONCLUSIONS This case emphasizes the importance of recognizing this extradural variant of schwannoma. Staged extracranial and intracranial approaches to these tumors may be necessary.

Angiomatous type of jugular foramen meningioma with neck extension : differential diagnosis from paraganglioma and schwannoma

Meningiomas involving the jugular foramen and parapharyngeal space are extremely rare. They most commonly occur intracranially and then extend to the extracranial region through the foramen of the skull base, such as jugular foramen. Clinically, these tumors mimic the more common glomus jugulare tumor. Preoperative diagnosis can be correct on the basis of the characteristic imaging findings.