Usefulness of neurophysiologic techniques in stereotactic subthalamic nucleus stimulation for advanced Parkinson's disease.

OBJECTIVE: The objectives of this study are to determine the impact of neurophysiologic guidance on subthalamic nucleus (STN) targeting and to assess its safety and effectiveness. METHODS: We have compared the initial theoretic anatomic target (TAT) of the STN with the final microrecording guided coordinates in 15 consecutive patients with bilaterally implanted electrodes in the STN. The clinical results and adverse effects are also reported. All comparisons were done through a paired Student's t test and Pearson's correlation test. RESULTS: Neurophysiological guidance changed the target coordinates in 26 of the procedures. The mean correction applied to the TAT in order to place the electrode in its definite location was 0.4 mm (+/-0.8, range 0-3; P=0.03) in the medial-lateral axis, 1.6 mm (+/-1.2, range 0-5; P=0.01) in the anterior-posterior plane and 0.8 mm (+/-0.8, range 0-3; P=0.26) in the vertical axis. The mean number of microrecording tracks employed to localize each STN was 2.8+/-1.8 (range 1-8) tracks. After surgery, the total UPDRS motor score in the off medication condition improved by 65.9%; UPDRS-II scores were reduced by 71.8% and Schwab and England scores improved by 45.3%. No intraoperative hemorrhages occurred in this series. CONCLUSIONS: Neurophysiological guidance is a safe and useful tool in order to improve and confirm target localization. The correction applied in the target resulted in a significant clinical improvement 6 months after surgery.

Levodopa withdrawal after bilateral subthalamic nucleus stimulation in advanced Parkinson disease.

CONTEXT: Subthalamic nucleus (STN) stimulation may be effective in ameliorating parkinsonian symptoms even to the extent to permit levodopa withdrawal. OBJECTIVES: To analyze the efficacy of STN stimulation in patients with Parkinson disease (PD) and to determine if levodopa may be withdrawn after surgery. DESIGN: Before-after trial. SETTING: Referral center, hospitalized care. PATIENTS: Fifteen patients with advanced PD. INTERVENTIONS: Microelectrode-guided bilateral STN high-frequency stimulation. OUTCOME MEASURES: Before surgery patients were evaluated in off-medication and on-medication conditions. Dopaminergic drug dosages were reduced after surgery, aiming for complete withdrawal. Six months after surgery, patients were reeavaluated in off- and on-medication conditions, with the stimulation turned on and off. RESULTS: Total Unified Parkinson's Disease Rating Scale (UPDRS) motor score in the off-medication condition improved by 65.9%; and axial symptoms, bradykinesia, rigidity, and tremor improved by 65.8%, 60.4%, 66.1%, and 81.1%, respectively. UPDRS part II scores were reduced by 71.8% and Schwab and England scores improved by 45.3%. Levodopa was withdrawn in 8 patients and the overall levodopa dose was reduced 80.4%. "Off" time was reduced 89.7% and the severity of dyskinesias decreased 80.6% after surgery. All results reached significance (P<.001). Stimulation of the STN achieved antiparkinsonian effect similar to that of treatment with levodopa. No life-threatening adverse effects occurred. CONCLUSIONS: Bilateral STN stimulation safely improves all parkinsonian symptoms, decreases or eliminates the need for levodopa, and ameliorates motor fluctuations and dyskinesias. Complete withdrawal of levodopa is feasible with this technique and the overall motor effect of STN stimulation is quantitatively comparable to that obtained with levodopa.

Prepulse modulation of the startle reaction and the blink reflex in normal human subjects.

Blink reflexes are usually considered the most representative and consistent response of the auditory startle reaction (ASR), and they are often the only response evaluated in human psychophysiological studies. However, auditory stimuli also induce an auditory blink reflex (ABR), the physiological characteristics and brainstem circuitry of which may be different from those of the ASR. This study aimed to investigate whether there were differences between the orbicularis oculi (OOc) responses elicited with the ABR (OOcABR) and those elicited with the ASR (OOcASR) regarding their behavior to prepulse modulation. For comparison, we also examined the OOc responses to supraorbital nerve stimulation (OOcEBR). Electromyographic responses were simultaneously recorded from the OOc, masseter (MAS) and sternocleidomastoid (SCM) muscles. ABRs were considered when auditory stimuli induced responses limited to the OOc, and ASRs were considered when responses were induced in all muscles recorded from. Prepulse stimuli were either a weak electrical stimulation at the third finger (somatosensory prepulse) or a weak acoustic tone (auditory prepulse) that preceded the response-eliciting stimuli by intervals ranging from 0 to 200 ms. Prepulse effects differed according to prepulse modality, but the OOcABR and the OOcASR were always modulated in the same way. In both responses, somatosensory prepulses induced facilitation from 20 to 50 ms, followed by inhibition beyond 75 ms, and auditory prepulses induced no facilitation but a significant inhibition beyond 30 ms. In the OOcEBR, both somatosensory and acoustic prepulses induced facilitation of R1 and inhibition of R2 beyond 30 ms. Our results suggest that the OOcABR and the OOcASR exhibit the same physiological behavior regarding prepulse modulation. It is hypothesized that prepulse facilitation is due to direct impingement of subthreshold excitatory inputs onto the facial motoneurons while prepulse inhibition results from the engagement of a presynaptic inhibitory circuit in the brainstem.