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  • Thalamic field potentials during deep brain stimulation of periventricular gray in chronic pain.

    3 July 2018

    Stimulation of the central gray matter areas has been used for the treatment of chronic pain for decades. To better understand the mechanism of action of such treatment we studied the effects of stimulation of the periventricular gray (PVG) on the sensory thalamus in two patients with chronic central pain. In each case, two electrodes were implanted in the PVG (Medtronic 3389) and the ventroposterolateral thalamic nucleus (Medtronic 3387), respectively, under guidance of CT/MRI image fusion. The PVG was stimulated in the frequency range of 2-100 Hz in alert patients while pain was assessed using the McGill-Melzack visual analogue scale. In addition, local field potentials (FPs) were recorded from the sensory thalamus during PVG stimulation. Maximum pain relief was obtained with 5-25 Hz stimulation while 50-100 Hz made the pain worse. This suggests that pain suppression was frequency dependent. Interestingly, we detected low frequency FPs at 0.2-0.4 Hz closely associated with the pain. During 5-25 Hz PVG stimulation the amplitude of this potential was significantly reduced and this was associated with marked pain relief. At the higher frequencies (50-100 Hz) however, there was no reduction in the FPs and no pain suppression. We have found an interesting correlation between thalamic activity and chronic pain. This curious low frequency potential may provide an objective index for quantifying chronic pain, and may hold further clues to the mechanism of action of PVG stimulation.

  • Bilateral internal globus pallidus stimulation for the treatment of spasmodic torticollis.

    3 July 2018

    Three patients with spasmodic torticollis (ST) obtained substantial benefit from bilateral globus pallidus internus (GPi) stimulation. Progressive improvement in ST occurred over several months but residual cervical dystonia remained. These results corroborate those obtained by Krauss et al. on three patients with ST.

  • Permanent tremor reduction during thalamic stimulation in multiple sclerosis.

    3 July 2018

    BACKGROUND: Unlike thalamic lesioning, thalamic stimulation is considered a reversible treatment for tremor. However, tremor in multiple sclerosis (MS) can sometimes permanently improve during thalamic stimulation. Such 'permanent tremor reduction' (PTR) has been attributed to limb weakness preventing tremor expression. In this study, 11 consecutive patients with MS tremor treated with thalamic stimulation were assessed for PTR. Eighteen upper limbs had tremor, of which 16 received contralateral stimulation. METHODS: Tremor severity and limb strength were assessed preoperatively, early postoperatively (within 1 year) and late postoperatively (after 3 years). Tremor severity was rated using validated clinical scales both on and off stimulation. Following explantation, the parenchyma surrounding three electrode tracts was examined with MRI. RESULTS: At final review (mean 5.2 years) PTR was evident in 11 of the 18 upper limbs with tremor. PTR often rendered stimulation redundant. PTR could occur when limb strength was conserved and could arise remotely from the initial surgery. PTR was significant (and universal) in limbs that received long-term (>2 years) effective (tremor suppressing) stimulation. PTR was not a significant finding in limbs that had not received long-term, effective stimulation. Contralateral to a limb with PTR, MRI revealed a thalamic lesion adjacent to the electrode tract. Thalamic lesions were not identified contralateral to two limbs without PTR. CONCLUSIONS: MS tremor often permanently improves during thalamic stimulation, even when limb strength is conserved. PTR may simply reflect natural history. Alternatively, these findings appear consistent with the recent proposal that thalamic stimulation in MS might promote local 'demyelinative lesioning.'

  • Neurophysiologic intervention in deep brain stimulation treatment for movement disorders: a practical framework.

    3 July 2018

    Clinical neurophysiology has always played an important interventional role throughout the perioperative stages in functional neurosurgery. On the one hand, some neurophysiologic procedures have become an integrated part of neurosurgery. On the other hand, in deep brain stimulation, although the surgical electrode implantation is an essential step, the therapeutic effects are actually produced by electrically modulating the physiologic activity of the brain. We review the topic of neurophysiologic intervention in the deep brain stimulation for movement disorders by presenting the evidence derived from our own experiences based on an integrated group located at two hospitals in London and Oxford, UK, and mainly covering tremor caused by multiple sclerosis, Parkinson's disease and dystonia.

  • Somatotopic organization of the human periventricular gray matter.

    3 July 2018

    The periventricular gray (PVG) matter is an established anatomical target for chronic deep brain stimulation (DBS) in the treatment of certain intractable pain syndromes. Data relating to the representation of pain and other somatosensory modalities within the PVG in humans are negligible. We examined the character and location of somatosensory responses elicited by electrical stimulation along the length of the PVG in a patient who underwent unilateral DBS for intractable nociceptive head pain. Consistent responses were obtained and indicated the presence of a somatotopic representation in this region. The contralateral lower limb was represented cranially, followed by the upper limb and trunk, with the face area located caudally, near the level of the superior colliculi. Bilateral representation was only observed in the forehead and scalp.

  • Increased risk of lead fracture and migration in dystonia compared with other movement disorders following deep brain stimulation.

    3 July 2018

    Deep brain stimulation (DBS) therapy is a continually expanding field in the functional neurosurgical treatment of movement disorders. However, the occurrence of adverse events related to implanted hardware cannot be overlooked. We report on a specific feature noted in our experience of DBS-related complications. From 1998 until present we have found an overall rate of 5.3% of DBS electrode lead dysfunction (out of 133 patients) in our series (slipped leads 2.3%, lead fracture 3.8%). Interestingly, all of these failures occurred in dystonia patients (18.4% of all dystonia patients and 9.2% of all electrodes). We postulate on mechanisms that may explain why these complications predominate in this group of patients.