Efficacy of motor cortex stimulation in the treatment of neuropathic pain: a randomized double-blind trial

OBJECT: In this study the authors used a double-blind protocol to assess the efficacy of motor cortex stimulation (MCS) for treating neuropathic pain. METHODS: Eleven patients with unilateral neuropathic pain (visual analog scale [VAS] score 8-10) of different origins and topography were selected for MCS. A 20-contact grid was implanted through a craniotomy centered over the motor cortex contralateral to the painful area. The motor cortex strip was identified using neuroimages, somatosensory evoked potentials, acute electrical stimulation, and corticocortical evoked potentials. Subacute therapeutic stimulation trials allowed the authors to determine the most efficient pair of contacts to use for long-term MCS. The grid was replaced with a 4-contact electrode connected to an internalized stimulator. Bipolar stimulation at a 40-Hz frequency, 90-micro sec pulse width, amplitude 2-7 V, and 1 hour in "ON" and 4 hours in "OFF" mode was used. Pain was evaluated using the VAS, Bourhis, and McGill pain scales applied each month for 1 year. At Day 60 or 90, the stimulators were turned to OFF mode for 30 days in a randomized, double-blind fashion. The statistical tool used was the Wilcoxon test. RESULTS: Three patients did not report improvement in the subacute trial and were excluded from long-term MCS; the remaining patients underwent long-term stimulation. Significant improvement of pain was induced by MCS (p < 0.01); this persisted during the follow-up period. Turning stimulation to OFF mode increased pain significantly (p < 0.05). Improvement at 1 year was >or= 40% (40-86%) in all cases. CONCLUSIONS: Motor cortex stimulation is an efficient treatment for neuropathic pain, according to an evaluation facilitated by a double-blind maneuver. Subacute stimulation trials are recommended to determine the optimum motor cortex area to be stimulated and to identify nonresponders.     

Efficacy of motor cortex stimulation for intractable central neuropathic pain: comparison of stimulation parameters between post-stroke pain and other central pain

Motor cortex stimulation (MCS) has now become the preferred option for neurosurgical management of intractable central neuropathic pain such as post-stroke pain and trigeminal neuropathic pain. However, the efficacy of MCS for other central neuropathic pain such as pain resulting from spinal cord or brainstem lesions is unclear. We retrospectively reviewed 11 consecutive patients with intractable central neuropathic pain who underwent MCS in our institution. Eight patients had poststroke pain caused by thalamic hemorrhage (n = 5) or infarction (n = 3) (thalamic group). Two patients had postoperative neuropathic pain caused by spinal cord lesions, and one patient had facial pain caused by a brainstem lesion associated with multiple sclerosis (brainstem-spinal group). Visual analog scale and stimulation parameters were evaluated at 1 and 6 months postoperatively. MCS was effective for six of eight patients in the thalamic group, and all three patients in the brainstem-spinal group. These efficacies continued for 6 months after surgery without significant change in the stimulation parameters compared with the parameters at 1 month in both groups. The mean amplitude at 1 month and frequency at 6 months after surgery were significantly higher in the brainstem-spinal group than the thalamic group, although the patient number was small. MCS is effective for other central neuropathic pain, but higher intensity stimulation parameters may be necessary to gain adequate pain reduction.     

Improved Dexterity after Chronic Electrical Stimulation of the Motor Cortex for Central Pain: A Special Relevance for Thalamic Syndrome

Objectives: To demonstrate that motor cortex stimulation (MCS) could improve motor function in patients with neuropathic pain. Methods: In this prospective clinical study of 38 patients referred for MCS as treatment for their neuropathic pain, we collected any declaration of improvement in motor performance that could be attributed to MCS. Results: Ten patients (26%) declared a benefit in their motor function. Eight presented objective evidence of recovered dexterity for rapid alternating movements. A minor proportion had improvement in dystonic posture (n = 2), but none had detectable increased motor strength or tonus changes. Overall, 73% of the patients with limb ataxia declared a benefit after MCS. In 6 out of 10 patients (60%), the anatomic lesion responsible for pain was restricted to the lateral aspect of the thalamus. All of them had either clinical or electrophysiological evidence of lemniscal dysfunction (proprioceptive ataxia). No correlation was found between the scores of pain relief and the modification of motor status. The correlation between thalamic lesions and benefits in motor performance was significant (Fisher's exact test, two-tailed, p = 0.0017). Conclusions: Up to 26% of patients estimated that MCS improved their motor outcome through recovered dexterity and in cases of lateral thalamic lesions.     

Motor cortex stimulation for post-stroke pain using neuronavigation and evoked potentials: report of 3 cases

Although motor cortex stimulation (MCS) has been accepted as an effective therapeutic option for central pain, the efficacy of MCS widely varies among previous reports. In this report, we describe our recent trial for successful MCS in 3 patients with central pain due to cerebral stroke. Medical treatments were transiently effective, but gradually became ineffective in all of the cases. During surgery, the appropriate cortical target was determined by using neuronavigation, somatosensory evoked potential (SEP), and motor evoked potential (MEP). A flat, four-plate electrode was positioned on the dura mater parallel to the motor cortex. After surgery, pain almost resolved in 2 of 3 patients and markedly improved in another. The pain relief depended on their motor function. These findings strongly suggest that both patient selection and intraoperative monitoring for targeting the motor cortex are quite important for successful MCS, although further studies were essential.     

Invasive and non-invasive brain stimulation for treatment of neuropathic pain in patients with spinal cord injury: A review

Context

Past evidence has shown that invasive and non-invasive brain stimulation may be effective for relieving central pain.

Objective

To perform a topical review of the literature on brain neurostimulation techniques in patients with chronic neuropathic pain due to traumatic spinal cord injury (SCI) and to assess the current evidence for their therapeutic efficacy.

Methods

A MEDLINE search was performed using following terms: “Spinal cord injury”, “Neuropathic pain”, “Brain stimulation”, “Deep brain stimulation” (DBS), “Motor cortex stimulation” (MCS), “Transcranial magnetic stimulation” (TMS), “Transcranial direct current stimulation” (tDCS), “Cranial electrotherapy stimulation” (CES).

Results

Invasive neurostimulation therapies, in particular DBS and epidural MCS, have shown promise as treatments for neuropathic and phantom limb pain. However, the long-term efficacy of DBS is low, while MCS has a relatively higher potential with lesser complications that DBS. Among the non-invasive techniques, there is accumulating evidence that repetitive TMS can produce analgesic effects in healthy subjects undergoing laboratory-induced pain and in chronic pain conditions of various etiologies, at least partially and transiently. Another very safe technique of non-invasive brain stimulation – tDCS – applied over the sensory-motor cortex has been reported to decrease pain sensation and increase pain threshold in healthy subjects. CES has also proved to be effective in managing some types of pain, including neuropathic pain in subjects with SCI.

Conclusion

A number of studies have begun to use non-invasive neuromodulatory techniques therapeutically to relieve neuropathic pain and phantom phenomena in patients with SCI. However, further studies are warranted to corroborate the early findings and confirm different targets and stimulation paradigms. The utility of these protocols in combination with pharmacological approaches should also be explored.     

Treatment of central and neuropathic facial pain by chronic stimulation of the motor cortex: value of neuronavigation guidance systems for the localization of the motor cortex

Thirty two patients with refractory central and neuropathic pain of peripheral origin were treated by chronic stimulation of the motor cortex between May 1993 and January 1997. The mean follow-up was 27. 3 months. The first 24 patients were operated according to the technique described by Tsubokawa. The last 13 cases (8 new patients and 5 reinterventions) were operated by a technique including localization by superficial CT reconstruction of the central region and neuronavigator guidance. The position of the central sulcus was confirmed by the use of intraoperative somatosensory evoked potentials. The somatotopic organisation of the motor cortex was established peroperatively by studying the motor responses at stimulation of the motor cortex through the dura. Ten of the 13 patients with central pain (77%) and nine of the 12 patients with neuropathic facial pain had experienced substantial pain relief (75%). One of the 3 patients with post-paraplegia pain was clearly improved. A satisfactory result was obtained in one patient with pain related to plexus avulsion and in one patient with pain related to intercostal herpes zoster. None of the patients developed epileptic seizures. The position of the stimulating poles effective on pain corresponded to the somatotopic representation of the motor cortex. The neuronavigator localization and guidance technique proved to be most useful identifying the appropriate portion of the motor gyrus. It also allowed the establishment of reliable correlations between electrophysiological-clinical and anatomical data which may be used to improve the clinical results and possibly to extend the indications of this technique.     

Chronic motor cortex stimulation for phantom limb pain: a functional magnetic resonance imaging study: technical case report

OBJECTIVE AND IMPORTANCE: Chronic motor cortex stimulation has provided satisfactory control of pain in patients with central or neuropathic trigeminal pain. We used this technique in a patient who experienced phantom limb pain. Functional magnetic resonance imaging (fMRI) was used to guide electrode placement and to assist in understanding the control mechanisms involved in phantom limb pain. CLINICAL PRESENTATION: A 45-year-old man whose right arm had been amputated 2 years previously experienced phantom limb pain and phantom limb phenomena, described as the apparent possibility of moving the amputated hand voluntarily. He was treated with chronic motor cortex stimulation. INTERVENTION: Data from fMRI were used pre- and postoperatively to detect shoulder and stump cortical activated areas and the "virtual" amputated hand cortical area. These sites of preoperative fMRI activation were integrated in an infrared-based frameless stereotactic device for surgical planning. Phantom limb virtual finger movement caused contralateral primary motor cortex activation. Satisfactory pain control was obtained; a 70% reduction in the phantom limb pain was achieved on a visual analog scale. Postoperatively and under chronic stimulation, inhibiting effects on the primary sensorimotor cortex as well as on the contralateral primary motor and sensitive cortices were detected by fMRI studies. CONCLUSION: Chronic motor cortex stimulation can be used to relieve phantom limb pain and phantom limb phenomena. Integrated by an infrared-based frameless stereotactic device, fMRI data are useful in assisting the neurosurgeon in electrode placement for this indication. Pain control mechanisms and cortical reorganization phenomena can be studied by the use of fMRI.     

Traitement neurochirurgical de la douleur chronique

Neurosurgical treatment of pain used two kind of techniques: 1) Lesional techniques interrupt the transmission of nociceptive neural input by lesionning the nociceptive pathways (drezotomy, cordotomy, tractotomy…). They are indicated to treat morphine-resistant cancer pain and few cases of selected neuropathic pain. 2) Neuromodulation techniques try to decrease pain by reinforcing inhibitory and/or to limit activatory mechanisms. Chronic electrical stimulation of the nervous system (peripheral nerve stimulation, spinal cord stimulation, motor cortex stimulation…) is used to treat chronic neuropathic pain. Intrathecal infusion of analgesics (morphine, ziconotide…), using implantable pumps, allows to increase their efficacy and to reduce their side effects. These techniques can improve, sometimes dramatically, selected patients with severe and chronic pain, refractory to all other treatments. The quality of the analgesic outcome depends on the relevance of the indications.     

Motor cortex stimulation for phantom limb pain: comprehensive therapy with spinal cord and thalamic stimulation

The effects of spinal cord stimulation (SCS), deep brain stimulation (DBS) of the thalamic nucleus ventralis caudalis (VC) and motor cortex stimulation (MCS) were analyzed in 19 patients with phantom limb pain. All of the patients underwent SCS and, if the SCS failed to reduce the pain, the patients were considered for DBS and/or MCS. Satisfactory pain control for the long-term was achieved in 6 of 19 (32%) by SCS, 6 of 10 (60%) by DBS and 1 (20%) of 5 by MCS. SCS and DBS of the VC sometimes produced a dramatic effect on the pain, leading to a long pain-free interval and infrequent use of stimulation. The effects of both DBS of the VC and MCS were tested in four. One patient of them reported better pain control by MCS than by DBS, whereas two reported the opposite results. There is no evidence at present for an advantage of MCS over SCS and DBS of the VC in controlling phantom limb pain.     

Image-guided motor cortex stimulation in patients with central pain.

According to recent clinical data, motor cortex stimulation (MCS) is an alternative treatment for central pain syndromes. We present our minimally invasive technique of image guidance for the placement of the motor cortex-stimulating electrode and assess the clinical usefulness of both neuronavigation and vacuum headrest. Five patients suffering from central pain underwent MCS with the guidance of a frameless stereotactic system (BrainLab AG, Munich, Germany). The neuronavigation was used for identification of the precentral gyrus and accurate planning of the single burr hole. The exact location was reconfirmed by an intraoperative stimulation test. Postoperative clinical and neuroradiological evaluations were performed in each patient. The navigation system worked properly in all 5 neurosurgical cases. Determination of the placement of stimulating electrode was possible in every case. All patients obtained postoperative pain relief. No surgical complication occurred, and the postoperative course was uneventful in all patients. This preliminary experience may confirm image guidance as a useful tool for the surgery of MCS. Additionally, minimal and safe exposure can be achieved using a single burr hole and vacuum headrest.     

Recovery of pain control by intensive reprogramming after loss of benefit from motor cortex stimulation for neuropathic pain

INTRODUCTION: Motor cortex stimulation (MCS) may serve as an adjunct in managing neuropathic pain after other conservative and interventional methods have failed. However, the magnitude and duration of the benefit are highly variable, with a significant percentage of patients losing pain relief over time. We investigated whether intensive reprogramming could recapture the beneficial effects of MCS. METHODS: Six patients who had previously undergone MCS implantation for neuropathic pain but had lost benefit were brought back for 1-5 days of intensive reprogramming. Four patients were evaluated as inpatients while the others were seen as outpatients during multiple visits over several days. Several hours a day were spent with each patient. Patients completed visual analog scale (VAS) ratings at intervals throughout the reprogramming period to judge effectiveness of stimulation. Pre- and postadjustment VAS were compared using a paired t test. RESULTS: The patients' average age was 50 years (range 26-71). The diagnoses were trigeminal neuropathic pain (2 patients), complex regional pain syndrome I (2), phantom limb pain (1) and poststroke pain (1). The mean duration of pain was 6 years. The MCS benefit had initially lasted for a mean of 7.16 months (range 2-18 months). After reprogramming, 5 of 6 patients experienced improvement in pain. Average VAS scores decreased from 7.44 to 2.28 (p < 0.001) in those patients who responded to reprogramming. The average stimulation parameters in these patients were 5 V amplitude (range 1.7-10), 313 micros pulse width (range 240-390) and frequency of 84 Hz (range 55-130). Three patients experienced seizures during reprogramming. The mean seizure threshold was 8.9 V. No patient experienced seizures at their therapeutic settings. Pain control has been maintained after discharge. CONCLUSION: Intensive reprogramming can recapture the benefit of MCS in patients who have lost pain control. The use of broad dipoles using two contacts rather than one contact of the 1 x 4 electrode array improved the ability to recapture beneficial stimulation. There is a significant risk of seizures during aggressive reprogramming.     

Motor cortex stimulation in patients with Parkinson disease: 12-month follow-up in 4 patients

OBJECT: Since the initial 1991 report by Tsubokawa et al., stimulation of the M1 region of cortex has been used to treat chronic pain conditions and a variety of movement disorders. METHODS: A Medline search of the literature published between 1991 and the beginning of 2007 revealed 459 cases in which motor cortex stimulation (MCS) was used. Of these, 72 were related to a movement disorder. More recently, up to 16 patients specifically with Parkinson disease were treated with MCS, and a variety of results were reported. In this report the authors describe 4 patients who were treated with extradural MCS. RESULTS: Although there were benefits seen within the first 6 months in Unified Parkinson's Disease Rating Scale Part III scores (decreased by 60%), tremor was only modestly managed with MCS in this group, and most benefits seen initially were lost by the end of 12 months. CONCLUSIONS: Although there have been some positive findings using MCS for Parkinson disease, a larger study may be needed to better determine if it should be pursued as an alternative surgical treatment to DBS.     

Motor cortex stimulation for post-stroke pain: comparison of spinal cord and thalamic stimulation

We analyzed the effects of spinal cord stimulation (SCS), deep brain stimulation (DBS) of the thalamic nucleus ventralis caudalis (VC) and motor cortex stimulation (MCS) in 45 patients with post-stroke pain. Satisfactory pain control was obtained more frequently as the stimulation site was moved to higher levels (7% by SCS, 25% by DBS and 48% by MCS). A painful sensation was sometimes produced by stimulation of the VC as well as the post-central, pre-central and pre-frontal cortices. Such a sensation occurred less frequently as the stimulation site was moved to higher levels (50% at the VC, 39% at the post-central cortex, 6% at the pre-central cortex and 3% at the pre-frontal cortex). These findings imply that abnormal processing of nociceptive information develops at the level of deafferentation and spreads to higher levels to a varying extent. This may be one of the reasons why satisfactory pain control was obtained more frequently as the stimulation site was moved to higher levels.     

Increased regional cerebral blood flow in the contralateral thalamus after successful motor cortex stimulation in a patient with poststroke pain

The mechanisms underlying poststroke pain have not been clearly identified. Although motor cortex stimulation (MCS) sometimes reduces poststroke pain successfully, the exact mechanism is not yet known. For further investigation of the neural pathways involved in the processing of poststroke pain and in pain reduction by MCS, the authors used positron emission tomography (PET) scanning to determine significant changes in regional cerebral blood flow (rCBF). This 58-year-old right-handed man suffered from right-sided poststroke pain for which he underwent implantation of a stimulation electrode in the right motor cortex. After 30 minutes of stimulation, his pain was remarkably reduced (Visual Analog Scale scores decreased 8 to 1) and he felt warmth in his left arm. The rCBF was studied using PET scanning with 15O-labeled water when the patient was in the following states: before MCS (painful condition, no stimulation) and after successful MCS (painless condition, no stimulation). The images were analyzed using statistical parametric mapping software. State-dependent differences in global blood flow were covaried using analysis of covariance. Comparisons of the patient's rCBF in the painful condition with that in the painless condition revealed significant rCBF increases in the left rectus gyrus (BA11), left superior frontal lobe (BA9), left anterior cingulate gyms (BA32), and the left thalamus (p < 0.05, corrected). On the other hand, there were significant decreases in rCBF in the right superior temporal gyrus (BA22, p < 0.01, corrected) and the left middle occipital gyrus (BA19, p < 0.05, corrected). The efficacy of MCS was mainly related to increased synaptic activity in the thalamus, whereas the activations in the rectus gyrus, anterior cingulate gyrus, and superior frontal cortex as well as the inactivation of the superior temporal lobe may be related to emotional processes. This is the first report in which the contralateral thalamus was significantly activated and pain relief was achieved using MCS.     

Motor cortex stimulation: mild transient benefit in a primate model of Parkinson disease

OBJECT: The authors sought to examine the therapeutic efficacy of motor cortex stimulation (MCS) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated macaques and to characterize therapeutic differences with varying modes, frequencies, and durations of stimulation. METHODS: Motor cortex stimulation was delivered at currents below motor threshold and at frequencies between 5 and 150 Hz through epidural electrodes over the primary motor cortex. The animals were studied during and without MCS using video analysis, activity logging, and food retrieval tasks. Animals were examined using two different stimulation protocols. The first protocol consisted of 1 hour of MCS therapy daily. The second protocol exposed the animal to continuous MCS for more than 24 hours with at least 2 weeks between MCS treatments. CONCLUSIONS: Daily MCS yielded no consistent change in symptoms, but MCS at 2-week intervals resulted in significant increases in activity. Effects of biweekly MCS disappeared, however, within 24 hours of the onset of continuous MCS. In this study, MCS only temporarily reduced the severity of MPTP-induced parkinsonism.     

Intra-Operative Mapping of the Motor Cortex During Surgery in and Around the Motor Cortex

The intra-operative use of neurophysiological techniques allows reliable identification of the sensorimotor region, and constitutes a prerequisite for its anatomical and functional preservation. The present prospective study combines monopolar cortical stimulation (MCS) with the recording of phase reversal of somatosensory evoked potentials (SEP-PR) in a protocol for the intra-operative mapping of the motor cortex. Functional mapping of the motor cortex by SEP-PR and MCS was performed in 70 patients during surgery in and around the motor cortex. The central sulcus was identified by SEP-PR. Cortical motor mapping was then performed by monopolar anodal (400 Hz) stimulation. Motor responses were recorded by needle electrodes placed in the muscles of the contralateral extremities. Surgery was performed under general anaesthesia without muscle relaxants. Intra-operative localization of the central sulcus by SEP-PR was possible in 68 patients (97.14%). Motor evoked potentials (MEP) were elicited following MCS in 67 cases (95.7%). In 3 cases no MEP was recorded, not even after maximal stimulation intensity, the central sulcus being localized by SEP-PR only. On the other hand, MCS allowed localizing the motor cortex in the 2 cases with no recordable SEP-PR. Thus, combining SEP-PR and MCS allowed intra-operative localization of the sensorimotor cortex in 100% of the cases.     

Pain relief and functional recovery in patients with complex regional pain syndrome after motor cortex stimulation

In addition to pain and neurovegetative symptoms, patients with severe forms of complex regional pain syndrome (CRPS) develop a broad range of symptoms, including sensory disturbances, motor impairment and dystonic posturing. While most patients respond to medical therapy, some are considered refractory and become surgical candidates. To date, the most commonly used surgical procedure for CRPS has been spinal cord stimulation. This therapy often leads to important analgesic effects, but no sensory or motor improvements. We report on 2 patients with pain related to CRPS and severe functional deficits treated with motor cortex stimulation (MCS) who not only had significant analgesic effects, but also improvements in sensory and motor symptoms. In the long term (27 and 36 months after surgery), visual analog scale pain scores were improved by 60-70% as compared to baseline. There was also a significant increase in the range of motion in the joints of the affected limbs and an improvement in allodynia, hyperpathia and hypoesthesia. Positron emission tomography scan in both subjects revealed that MCS influenced regions involved in the circuitry of pain.     

Intraoperative electrocortical stimulation of Brodman area 4: a 10-year analysis of 255 cases

Background

Brain tumor surgery is limited by the risk of postoperative neurological deficits. Intraoperative neurophysiological examination techniques, which are based on the electrical excitability of the human brain cortex, are thus still indispensable for surgery in eloquent areas such as the primary motor cortex (Brodman Area 4).

Methods

This study analyzed the data obtained from a total of 255 cerebral interventions for lesions with direct contact to (121) or immediately adjacent to (134) Brodman Area 4 in order to optimize stimulation parameters and to search for direct correlation between intraoperative potential changes and specific surgical maneuvers when using monopolar cortex stimulation (MCS) for electrocortical mapping and continuous intraoperative neurophysiological monitoring.

Results

Compound muscle action potentials (CMAPs) were recorded from the thenar muscles and forearm flexors in accordance with the large representational area of the hand and forearm in Brodman Area 4. By optimizing the stimulation parameters in two steps (step 1: stimulation frequency and step 2: train sequence) MCS was successful in 91% (232/255) of the cases. Statistical analysis of the parameters latency, potential width and amplitude showed spontaneous latency prolongations and abrupt amplitude reductions as a reliable warning signal for direct involvement of the motor cortex or motor pathways.

Conclusion

MCS must be considered a stimulation technique that enables reliable qualitative analysis of the recorded potentials, which may thus be regarded as directly predictive. Nevertheless, like other intraoperative neurophysiological examination techniques, MCS has technical, anatomical and neurophysiological limitations. A variety of surgical and non-surgical influences can be reason for false positive or false negative measurements.     

Chronic postoperative pain after general anesthesia with or without a single-dose preincisional paravertebral nerve block in radical breast cancer surgery

Background and objectiveOver 50% of patients still experience pain a year after mastectomy with or without lymphadenectomy. We aimed to determine the association between anesthetic technique, acute postoperative pain intensity, and the development of chronic postoperative pain.Patients and methodsForty patients were randomly assigned to receive general anesthesia with or without a paravertebral nerve block for modified radical mastectomy. Postoperative pain was assessed on a visual analog scale at 60 minutes and 24 hours; the patients were also asked to respond to a telephone questionnaire on chronic pain 4 to 5 months later.ResultsNo significant differences in acute pain were observed. Twenty-nine responded to the telephone questionnaire. Only 1 patient in the paravertebral block group reported chronic neuropathic pain and none had phantom breast pain. Only 1 patient (6.7%) in the paravertebral block group reported chronic neuropathic pain and none had phantom breast pain. In the group that received general anesthesia alone, 1 patient reported phantom breast pain and 6 patients had neuropathic pain, associated with phantom breast pain in 2 cases (incidence of chronic pain 50%; P = .01, Fischer exact test; relative risk, 7.5, 95% confidence interval, 1.0-53.5). The incidences of myofascial pain (neck muscle tightness) were similar in the 2 groups.ConclusionsFour to 5 months after mastectomy, fewer cases of chronic pain developed in the group operated under general anesthesia with a preincisional paravertebral block than in the group that received only general anesthesia, with postoperative morphine chloride for analgesia.     

Motor cortex stimulation in patients with deafferentation pain: activation of the posterior insula and thalamus

OBJECT: The mechanisms underlying deafferentation pain are not well understood. Motor cortex stimulation (MCS) is useful in the treatment of this kind of chronic pain, but the detailed mechanisms underlying its effects are unknown. METHODS: Six patients with intractable deafferentation pain in the left hand were included in this study. All were righthanded and had a subdural electrode placed over the right precentral gyrus. The pain was associated with brainstem injury in one patient, cervical spine injury in one patient, thalamic hemorrhage in one patient, and brachial plexus avulsion in three patients. Treatment with MCS reduced pain; visual analog scale (VAS) values for pain were 82 +/- 20 before MCS and 39 +/- 20 after MCS (mean +/- standard error). Regional cerebral blood flow (rCBF) was measured by positron emission tomography with H2(15)O before and after MCS. The obtained images were analyzed with statistical parametric mapping software (SPM99). RESULTS: Significant rCBF increases were identified after MCS in the left posterior thalamus and left insula. In the early post-MCS phase, the left posterior insula and right orbitofrontal cortex showed significant rCBF increases, and the right precentral gyrus showed an rCBF decrease. In the late post-MCS phase, a significant rCBF increase was detected in the left caudal part of the anterior cingulate cortex (ACC). CONCLUSIONS: These results suggest that MCS modulates the pathways from the posterior insula and orbitofrontal cortex to the posterior thalamus to upregulate the pain threshold and pathways from the posterior insula to the caudal ACC to control emotional perception. This modulation results in decreased VAS scores for deafferentation pain.