Efficacy of deep brain stimulation of the subthalamic nucleus versus globus pallidus internus on sensory complaints.

Pain control after deep brain stimulation (DBS) in Parkinson's disease (PD) remains unclear. Following six months, subthalamic (STN)-DBS reduced sensory complaints related to parkinsonism and bodily discomfort, increasing central beta-endorphin level. Pallidal GPi-DBS decreased bodily discomfort and beta-endorphin levels. Unexplained pain by other conditions and bodily discomfort were negatively correlated with beta-endorphin levels. Thus, DBS regulates central opioids, and prioritizing STN is important for PD patients with significant sensory complications.

Systemic and Peripheral Mechanisms of Cortical Stimulation-Induced Analgesia and Refractoriness in a Rat Model of Neuropathic Pain.

Epidural motor cortex stimulation (MCS) is an effective treatment for refractory neuropathic pain; however, some individuals are unresponsive. In this study, we correlated the effectiveness of MCS and refractoriness with the expression of cytokines, neurotrophins, and nociceptive mediators in the dorsal root ganglion (DRG), sciatic nerve, and plasma of rats with sciatic neuropathy. MCS inhibited hyperalgesia and allodynia in two-thirds of the animals (responsive group), and one-third did not respond (refractory group). Chronic constriction injury (CCI) increased IL-1ß in the nerve and DRG, inhibited IL-4, IL-10, and IL-17A in the nerve, decreased ß-endorphin, and enhanced substance P in the plasma, compared to the control. Responsive animals showed decreased NGF and increased IL-6 in the nerve, accompanied by restoration of local IL-10 and IL-17A and systemic ß-endorphin. Refractory animals showed increased TNF-α and decreased IFNγ in the nerve, along with decreased TNF-α and IL-17A in the DRG, maintaining low levels of systemic ß-endorphin. Our findings suggest that the effectiveness of MCS depends on local control of inflammatory and neurotrophic changes, accompanied by recovery of the opioidergic system observed in neuropathic conditions. So, understanding the refractoriness to MCS may guide an improvement in the efficacy of the technique, thus benefiting patients with persistent neuropathic pain.

Does TRODAT-1 SPECT Uptake Correlate with Cerebrospinal Fluid α-Synuclein Levels in Mid-Stage Parkinson's Disease?

BACKGROUND: Parkinson's disease (PD) is characterized by a progressive loss of nigrostriatal dopaminergic neurons with impaired motor and non-motor symptoms. It has been suggested that motor asymmetry could be caused due to an imbalance in dopamine levels, as visualized by dopamine transporter single emission computed tomography test (DAT-SPECT), which might be related to indirect measures of neurodegeneration, evaluated by the Montreal Cognitive Assessment (MOCA) and α-synuclein levels in the cerebrospinal fluid (CSF). Therefore, this study aimed to understand the correlation between disease laterality, DAT-SPECT, cognition, and α-synuclein levels in PD. METHODS: A total of 28 patients in the moderate-advanced stage of PD were subjected to neurological evaluation, TRODAT-1-SPECT/CT imaging, MOCA, and quantification of the levels of α-synuclein. RESULTS: We found that α-synuclein in the CSF was correlated with global cognition (positive correlation, r2 = 0.3, p = 0.05) and DAT-SPECT concentration in the putamen (positive correlation, r2 = 0.4, p = 0.005), and striatum (positive correlation, r2 = 0.2, p = 0.03), thus working as a neurodegenerative biomarker. No other correlations were found between DAT-SPECT, CSF α-synuclein, and cognition, thus suggesting that they may be lost with disease progression. CONCLUSIONS: Our data highlight the importance of understanding the dysfunction of the dopaminergic system in the basal ganglia and its complex interactions in modulating cognition.

Non-motor effects of deep brain stimulation in Parkinson's disease motor subtypes.

INTRODUCTION: Deep brain stimulation (DBS) is a well-established treatment for patients with Parkinson's disease (PD) improving quality of life, motor, and non-motor symptoms. However, non-motor effects in PD subtypes are understudied. We hypothesized that patients with 'postural instability and gait difficulty' (PIGD) experience more beneficial non-motor effects than 'tremor-dominant' patients undergoing DBS for PD. METHODS: In this prospective, observational, international multicentre study with a 6-month follow-up, we assessed the Non-Motor Symptom Scale (NMSS) as primary and the following secondary outcomes: Unified PD Rating Scale-motor examination (UPDRS-III), Scales for Outcomes in PD (SCOPA)-activities of daily living (ADL) and -motor complications, PDQuestionnaire-8 (PDQ-8), and levodopa-equivalent daily dose (LEDD). We analysed within-group longitudinal changes with Wilcoxon signed-rank test and Benjamini-Hochberg correction for multiple comparisons. Additionally, we explored outcome between-group differences of motor subtypes with Mann-Whitney U-tests. RESULTS: In 82 PIGD and 33 tremor-dominant patients included in this study, baseline NMSS total scores were worse in PIGD patients, both groups experienced postoperative improvements of the NMSS sleep/fatigue domain, and between-group differences in postoperative outcomes were favourable in the PIGD group for the NMSS total and miscellaneous domain scores. CONCLUSIONS: This study provides evidence of a favourable outcome of total non-motor burden in PIGD compared to tremor-dominant patients undergoing DBS for PD. These differences of clinical efficacy on non-motor aspects should be considered when advising and monitoring patients with PD undergoing DBS.

Use of Objective Outcomes Measures to Verify the Effects of ICF-Based Gait Treatment in Huntington's Disease Patient on Globus Pallidus Deep Brain Stimulation: A Case Report.

In advanced stages of in Huntington's disease (HD) gait impairments and severe chorea are usually medication-refractory. The long-term effects on gait in HD of physiotherapy ICF-based management post- globus pallidus deep brain stimulation (GPi DBS) are not well-established. Physiotherapy has been recognized as an essential element in HD treatment. Here, we present a case report of a 56-year-old woman with HD on the advanced stage and severe chorea medication-refractory after GPi-DBS. We performed multidisciplinary motor assessments ICF-based to identify the disability at clinical and home-setting, including environmental and personal factors before and after GPi-DBS surgery and at 11-time points follow-up. The surgery was very successful and directly post GPi-DBS, there were a significant improvement in chorea and a substantial decrease in medication dose. A framework ICF- based physiotherapy protocol with external cues was developed to improve gait was delivered post-surgery and was continued three times/week during 18-months. Physiotherapy sessions consisted of a personalized protocol of exercises with functional movements, balance, and gait training with external cues. Improvements in gait were observed in 3-months post-intervention and were more expressive in 6-months follow-up. Our patient improved substantially HD motor symptoms and her quality of life after GPi-DBS intervention and a physiotherapy program ICF-based. The objective outcomes measures used to assess gait have served as endpoints to assessing the patient's motor profile during the pre-operative period. Assessments were helpful to verify the efficacy of the multidisciplinary intervention in long-term. Conclusion: Periodically assessing function and disability using outcome improvements may support clinicians' decisions about DBS, medication adjustments and guide physiotherapists to personalize the ICF-based intervention.

Motor cortex stimulation for chronic neuropathic pain: results of a double-blind randomized study.

Motor cortex stimulation via surgically implanted electrodes has been used as an off-label treatment for chronic neuropathic pain, but its efficacy has not been fully established. We aimed to objectively study the efficacy of motor cortex stimulation and characterize potential predictors of response. In this randomized, double-blind, sham-controlled, single centre trial, we recruited 18 patients with chronic neuropathic pain who did not adequately respond to conventional treatment and had a numerical pain rating scale (NRS) score ≥6. Patients were initially assigned to receive 3 months of active ('on') or sham ('off') stimulation in a double-blind cross-over phase. This was followed by a 3-month single-blind phase, and 6 months of open-label follow-up. A meaningful response in our trial was defined as a ≥30% or 2-point reduction in NRS scores during active stimulation. Using Bayesian statistics, we found a 41.4% probability of response towards on versus off motor cortex stimulation. The probability of improvement during active stimulation (double-blind, single-blind and open-label phases) compared to baseline was 47.2-68.5%. Thirty nine per cent of the patients were considered long-term responders, 71.4% of whom had facial pain, phantom limb pain or complex regional pain syndrome. In contrast, 72.7% of non-responders had either post-stroke pain or pain associated with brachial plexus avulsion. Thirty-nine per cent of patients had a substantial postoperative analgesic effect after electrode insertion in the absence of stimulation. Individuals with diagnoses associated with a good postoperative outcome or those who developed an insertional effect had a near 100% probability of response to motor cortex stimulation. In summary, we found that ∼40% of patients responded to motor cortex stimulation, particularly those who developed an insertional effect or had specific clinical conditions that seemed to predict an appropriate postoperative response.

Motor Cortex Stimulation Reversed Hypernociception, Increased Serotonin in Raphe Neurons, and Caused Inhibition of Spinal Astrocytes in a Parkinson's Disease Rat Model.

Persistent pain is a prevalent symptom of Parkinson's disease (PD), which is related to the loss of monoamines and neuroinflammation. Motor cortex stimulation (MCS) inhibits persistent pain by activating the descending analgesic pathways; however, its effectiveness in the control of PD-induced pain remains unclear. Here, we evaluated the analgesic efficacy of MCS together with serotonergic and spinal glial modulation in an experimental PD (ePD) rat model. Wistar rats with unilateral striatal 6-OHDA and MCS were assessed for behavioral immobility and nociceptive responses. The immunoreactivity of dopamine in the substantia nigra and serotonin in the nucleus raphe magnus (NRM) and the neuronal, astrocytic, and microglial activation in the dorsal horn of the spinal cord were evaluated. MCS, without interfering with dopamine loss, reversed ePD-induced immobility and hypernociception. This response was accompanied by an exacerbated increase in serotonin in the NRM and a decrease in neuronal and astrocytic hyperactivation in the spinal cord, without inhibiting ePD-induced microglial hypertrophy and hyperplasia. Taken together, MCS induces analgesia in the ePD model, while restores the descending serotonergic pathway with consequent inhibition of spinal neurons and astrocytes, showing the role of MCS in PD-induced pain control.

Bilateral Amygdala Radio-Frequency Ablation for Refractory Aggressive Behavior Alters Local Cortical Thickness to a Pattern Found in Non-refractory Patients.

Aggressive behaviors comprise verbal and/or physical aggression directed toward oneself, others, or objects and are highly prevalent among psychiatric patients, especially patients diagnosed with autism spectrum disorder and severe intellectual disabilities. Some of these patients are considered refractory to treatment, and functional neurosurgery targeting the amygdala can result in widespread plastic brain changes that might reflect ceasing of some abnormal brain function, offering symptom alleviation. This study investigated cortical thickness changes in refractory aggressive behavior patients that were treated with bilateral amygdala ablation and compared to control patients presenting non-refractory aggressive behavior [three refractory and seven non-refractory patients, all males diagnosed with autism spectrum disorder (ASD) and intellectual disabilities]. The Overt Aggression Scale (OAS) was used to quantify behavior and magnetic resonance imaging was performed to investigate cortical thickness. Before surgery, both groups presented similar total OAS score, however refractory patients presented higher physical aggression against others. After surgery the refractory group showed 88% average reduction of aggressive behavior. Imaging analysis showed that while refractory patients present an overall reduction in cortical thickness compared to non-refractory patients across both timepoints, the local pattern of thickness difference found in areas of the neurocircuitry of aggressive behavior present before surgery is diminished and no longer detected after surgery. These results corroborate the hypotheses on induction of widespread neuronal plasticity following functional neurosurgical procedures resulting in modifications in brain morphology and improvement in behavior. Further studies are necessary to determine the underlying cause of these morphological changes and to better understand and improve treatment options.

Use of computational fluid dynamics for 3D fiber tract visualization on human high-thickness histological slices: histological mesh tractography.

Understanding the intricate three-dimensional relationship between fiber bundles and subcortical nuclei is not a simple task. It is of paramount importance in neurosciences, especially in the field of functional neurosurgery. The current methods for in vivo and post mortem fiber tract visualization have shortcomings and contributions to the field are welcome. Several tracts were chosen to implement a new technique to help visualization of white matter tracts, using high-thickness histology and dark field images. Our study describes the use of computational fluid dynamic simulations for visualization of 3D fiber tracts segmented from dark field microscopy in high-thickness histological slices (histological mesh tractography). A post mortem human brain was MRI scanned prior to skull extraction, histologically processed and serially cut at 430 µm thickness as previously described by our group. High-resolution dark field images were used to segment the outlines of the structures. These outlines served as basis for the construction of a 3D structured mesh, were a Finite Volume Method (FVM) simulation of water flow was performed to generate streamlines representing the geometry. The simulations were accomplished by an open source computer fluid dynamics software. The resulting simulation rendered a realistic 3D impression of the segmented anterior commissure, the left anterior limb of the internal capsule, the left uncinate fascicle, and the dentato-rubral tracts. The results are in line with clinical findings, diffusion MR imaging and anatomical dissection methods.

Refractoriness of aggressive behaviour to pharmacological treatment: cortical thickness analysis in autism spectrum disorder.

Aggressive behaviour is a highly prevalent and devastating condition in autism spectrum disorder resulting in impoverished quality of life. Gold-standard therapies are ineffective in about 30% of patients leading to greater suffering. We investigated cortical thickness in individuals with autism spectrum disorder with pharmacological-treatment-refractory aggressive behaviour compared with those with non-refractory aggressive behaviour and observed a brain-wide pattern of local increased thickness in key areas related to emotional control and overall decreased cortical thickness in those with refractory aggressive behaviour, suggesting refractoriness could be related to specific morphological patterns. Elucidating the neurobiology of refractory aggressive behaviour is crucial to provide insights and potential avenues for new interventions.

Neurochemical effects of motor cortex stimulation in the periaqueductal gray during neuropathic pain

OBJECTIVE Motor cortex stimulation (MCS) is a neurosurgical technique used to treat patients with refractory neuropathic pain syndromes. MCS activates the periaqueductal gray (PAG) matter, which is one of the major centers of the descending pain inhibitory system. However, the neurochemical mechanisms in the PAG that underlie the analgesic effect of MCS have not yet been described. The main goal of this study was to investigate the neurochemical mechanisms involved in the analgesic effect induced by MCS in neuropathic pain. Specifically, we investigated the release of g-aminobutyric acid (GABA), glycine, and glutamate in the PAG and performed pharmacological antagonism experiments to validate of our findings. METHODS Male Wistar rats with surgically induced chronic constriction of the sciatic nerve, along with sham-operated rats and naive rats, were implanted with both unilateral transdural electrodes in the motor cortex and a microdialysis guide cannula in the PAG and subjected to MCS. The MCS was delivered in single 15-minute sessions. Neurotransmitter release was evaluated in the PAG before, during, and after MCS. Quantification of the neurotransmitters GABA, glycine, and glutamate was performed using a high-performance liquid chromatography system. The mechanical nociceptive threshold was evaluated initially, on the 14th day following the surgery, and during the MCS. In another group of neuropathic rats, once the analgesic effect after MCS was confirmed by the mechanical nociceptive test, rats were microinjected with saline or a glycine antagonist (strychnine), a GABA antagonist (bicuculline), or a combination of glycine and GABA antagonists (strychnine+bicuculline) and reevaluated for the mechanical nociceptive threshold during MCS. RESULTS MCS reversed the hyperalgesia induced by peripheral neuropathy in the rats with chronic sciatic nerve constriction and induced a significant increase in the glycine and GABA levels in the PAG in comparison with the naive and sham-treated rats. The glutamate levels remained stable under all conditions. The antagonism of glycine, GABA, and the combination of glycine and GABA reversed the MCS-induced analgesia. CONCLUSIONS These results suggest that the neurotransmitters glycine and GABA released in the PAG may be involved in the analgesia induced by cortical stimulation in animals with neuropathic pain. Further investigation of the mechanisms involved in MCS-induced analgesia may contribute to clinical improvements for the treatment of persistent neuropathic pain syndromes

Neurochemical effects of motor cortex stimulation in the periaqueductal gray during neuropathic pain

OBJECTIVE Motor cortex stimulation (MCS) is a neurosurgical technique used to treat patients with refractory neuropathic pain syndromes. MCS activates the periaqueductal gray (PAG) matter, which is one of the major centers of the descending pain inhibitory system. However, the neurochemical mechanisms in the PAG that underlie the analgesic effect of MCS have not yet been described. The main goal of this study was to investigate the neurochemical mechanisms involved in the analgesic effect induced by MCS in neuropathic pain. Specifically, we investigated the release of g-aminobutyric acid (GABA), glycine, and glutamate in the PAG and performed pharmacological antagonism experiments to validate of our findings. METHODS Male Wistar rats with surgically induced chronic constriction of the sciatic nerve, along with sham-operated rats and naive rats, were implanted with both unilateral transdural electrodes in the motor cortex and a microdialysis guide cannula in the PAG and subjected to MCS. The MCS was delivered in single 15-minute sessions. Neurotransmitter release was evaluated in the PAG before, during, and after MCS. Quantification of the neurotransmitters GABA, glycine, and glutamate was performed using a high-performance liquid chromatography system. The mechanical nociceptive threshold was evaluated initially, on the 14th day following the surgery, and during the MCS. In another group of neuropathic rats, once the analgesic effect after MCS was confirmed by the mechanical nociceptive test, rats were microinjected with saline or a glycine antagonist (strychnine), a GABA antagonist (bicuculline), or a combination of glycine and GABA antagonists (strychnine+bicuculline) and reevaluated for the mechanical nociceptive threshold during MCS. RESULTS MCS reversed the hyperalgesia induced by peripheral neuropathy in the rats with chronic sciatic nerve constriction and induced a significant increase in the glycine and GABA levels in the PAG in comparison with the naive and sham-treated rats. The glutamate levels remained stable under all conditions. The antagonism of glycine, GABA, and the combination of glycine and GABA reversed the MCS-induced analgesia. CONCLUSIONS These results suggest that the neurotransmitters glycine and GABA released in the PAG may be involved in the analgesia induced by cortical stimulation in animals with neuropathic pain. Further investigation of the mechanisms involved in MCS-induced analgesia may contribute to clinical improvements for the treatment of persistent neuropathic pain syndromes

Non-motor outcomes depend on location of neurostimulation in Parkinson's disease.

Deep brain stimulation of the subthalamic nucleus is an effective and established therapy for patients with advanced Parkinson's disease improving quality of life, motor symptoms and non-motor symptoms. However, there is a considerable degree of interindividual variability for these outcomes, likely due to variability in electrode placement and stimulation settings. Here, we present probabilistic mapping data from a prospective, open-label, multicentre, international study to investigate the influence of the location of subthalamic nucleus deep brain stimulation on non-motor symptoms in patients with Parkinson's disease. A total of 91 Parkinson's disease patients undergoing bilateral deep brain stimulation of the subthalamic nucleus were included, and we investigated NMSScale, NMSQuestionnaire, Scales for Outcomes in Parkinson's disease-motor examination, -activities of daily living, and -motor complications, and Parkinson's disease Questionnaire-8 preoperatively and at 6-month follow-up after surgery. Leads were localized in standard space using the Lead-DBS toolbox and individual volumes of tissue activated were calculated based on clinical stimulation settings. Probabilistic stimulation maps and non-parametric permutation statistics were applied to identify voxels with significant above or below average improvement for each scale and analysed using the DISTAL atlas. All outcomes improved significantly at follow-up. Significant spatial distribution patterns of neurostimulation were observed for NMSScale total score and its mood/apathy and attention/memory domains. For both domains, voxels associated with below average improvement were mainly located dorsal to the subthalamic nucleus. In contrast, above average improvement for mood/apathy was observed in the ventral border region of the subthalamic nucleus and in its sensorimotor subregion and for attention/memory in the associative subregion. A trend was observed for NMSScale sleep domain showing voxels with above average improvement located ventral to the subthalamic nucleus. Our study provides evidence that the interindividual variability of mood/apathy, attention/memory, and sleep outcomes after subthalamic nucleus deep brain stimulation depends on the location of neurostimulation. This study highlights the importance of holistic assessments of motor and non-motor aspects of Parkinson's disease to tailor surgical targeting and stimulation parameter settings to patients' personal profiles.

Parkinson's disease and pain: Modulation of nociceptive circuitry in a rat model of nigrostriatal lesion.

Parkinson's disease (PD) is a neurodegenerative disorder that causes progressive dysfunction of dopaminergic and non-dopaminergic neurons, generating motor and nonmotor signs and symptoms. Pain is reported as the most bothersome nonmotor symptom in PD; however, pain remains overlooked and poorly understood. In this study, we evaluated the nociceptive behavior and the descending analgesia circuitry in a rat model of PD. Three independent experiments were performed to investigate: i) thermal nociceptive behavior; ii) mechanical nociceptive behavior and dopaminergic repositioning; and iii) modulation of the pain control circuitry. The rat model of PD, induced by unilateral striatal 6-hydroxydopamine (6-OHDA), did not interfere with thermal nociceptive responses; however, the mechanical nociceptive threshold was decreased bilaterally compared to that of naive or striatal saline-injected rats. This response was reversed by apomorphine or levodopa treatment. Striatal 6-OHDA induced motor impairments and reduced dopaminergic neuron immunolabeling as well as the pattern of neuronal activation (c-Fos) in the substantia nigra ipsilateral (IPL) to the lesion. In the midbrain periaqueductal gray (PAG), 6-OHDA-induced lesion increased IPL and decreased contralateral PAG GABAergic labeling compared to control. In the dorsal horn of the spinal cord, lesioned rats showed bilateral inhibition of enkephalin and µ-opioid receptor labeling. Taken together, we demonstrated that the unilateral 6-OHDA-induced PD model induces bilateral mechanical hypernociception, which is reversed by dopamine restoration, changes in the PAG circuitry, and inhibition of spinal opioidergic regulation, probably due to impaired descending analgesic control. A better understanding of pain mechanisms in PD patients is critical for developing better therapeutic strategies to improve their quality of life.

Neurochemical effects of motor cortex stimulation in the periaqueductal gray during neuropathic pain.

OBJECTIVE: Motor cortex stimulation (MCS) is a neurosurgical technique used to treat patients with refractory neuropathic pain syndromes. MCS activates the periaqueductal gray (PAG) matter, which is one of the major centers of the descending pain inhibitory system. However, the neurochemical mechanisms in the PAG that underlie the analgesic effect of MCS have not yet been described. The main goal of this study was to investigate the neurochemical mechanisms involved in the analgesic effect induced by MCS in neuropathic pain. Specifically, we investigated the release of γ-aminobutyric acid (GABA), glycine, and glutamate in the PAG and performed pharmacological antagonism experiments to validate of our findings. METHODS: Male Wistar rats with surgically induced chronic constriction of the sciatic nerve, along with sham-operated rats and naive rats, were implanted with both unilateral transdural electrodes in the motor cortex and a microdialysis guide cannula in the PAG and subjected to MCS. The MCS was delivered in single 15-minute sessions. Neurotransmitter release was evaluated in the PAG before, during, and after MCS. Quantification of the neurotransmitters GABA, glycine, and glutamate was performed using a high-performance liquid chromatography system. The mechanical nociceptive threshold was evaluated initially, on the 14th day following the surgery, and during the MCS. In another group of neuropathic rats, once the analgesic effect after MCS was confirmed by the mechanical nociceptive test, rats were microinjected with saline or a glycine antagonist (strychnine), a GABA antagonist (bicuculline), or a combination of glycine and GABA antagonists (strychnine+bicuculline) and reevaluated for the mechanical nociceptive threshold during MCS. RESULTS: MCS reversed the hyperalgesia induced by peripheral neuropathy in the rats with chronic sciatic nerve constriction and induced a significant increase in the glycine and GABA levels in the PAG in comparison with the naive and sham-treated rats. The glutamate levels remained stable under all conditions. The antagonism of glycine, GABA, and the combination of glycine and GABA reversed the MCS-induced analgesia. CONCLUSIONS: These results suggest that the neurotransmitters glycine and GABA released in the PAG may be involved in the analgesia induced by cortical stimulation in animals with neuropathic pain. Further investigation of the mechanisms involved in MCS-induced analgesia may contribute to clinical improvements for the treatment of persistent neuropathic pain syndromes.

Quality of Life After Motor Cortex Stimulation: Clinical Results and Systematic Review of the Literature.

BACKGROUND: Motor cortex stimulation (MCS) is routinely used for the treatment of chronic neuropathic pain but its effect on quality of life remains uncertain. OBEJCTIVE: To systematically review the published literature on MCS and quality of life and report the effects of this therapy in a series of patients prospectively followed in our center. METHODS: The systematic literature review was conducted using the search words "motor cortex stimulation and pain and neurosurgery" and "motor cortex stimulation and pain and quality of life." Quality of life in our clinical trial was investigated in a series of 10 patients with chronic neuropathic pain prospectively followed for 12 mo after MCS. RESULTS: Two hundred eighteen nonreplicated articles were pooled for analysis. Of these, 6 described measures of quality of life in the pre- and postoperative period. In these studies, 64 patients with different clinical conditions associated with neuropathic pain were followed for 6 to 84 mo after MCS surgery. Improvement in quality of life ranged from 35% to 85%. In our clinical series, visual analog scale (VAS), SF-12 physical (PhysCS), and mental scores (MenCS) recorded 12 mo after MCS were improved by 60 ± 10% (P = .002), 50 ± 13% (P = .002), and 22 ± 6% (P = .01), respectively. No significant correlation was found between postoperative improvement in pain and either PhysCS (r = 0.18; P = .6) or MenCS (r = -0.24; P = .5). CONCLUSION: MCS improves quality of life in patients with chronic refractory neuropathic pain. Additional factors other than a simple analgesic effect may contribute to these results.