New pain following cordotomy: clinical features, mechanisms, and clinical importance

Pain in the Context of Sensory Deafferentation

Pain that accompanies deafferentation is one of the most mysterious and misunderstood medical conditions. Prevalence rates for the assorted conditions vary considerably but the most reliable estimates are greater than 50% for strokes involving the somatosensory system, brachial plexus avulsions, spinal cord injury, and limb amputation, with controversy surrounding the mechanistic contributions of deafferentation to ensuing neuropathic pain syndromes. Deafferentation pain has also been described for loss of other body parts (e.g., eyes and breasts) and may contribute to between 10% and upwards of 30% of neuropathic symptoms in peripheral neuropathies. There is no pathognomonic test or sign to identify deafferentation pain, and part of the controversy surrounding it stems from the prodigious challenges in differentiating cause and effect. For example, it is unknown whether cortical reorganization causes pain or is a byproduct of pathoanatomical changes accompanying injury, including pain. Similarly, ascertaining whether deafferentation contributes to neuropathic pain, or whether concomitant injury to nerve fibers transmitting pain and touch sensation leads to a deafferentation-like phenotype can be clinically difficult, although a detailed neurologic examination, functional imaging, and psychophysical tests may provide clues. Due in part to the concurrent morbidities, the physical, psychologic, and by extension socioeconomic costs of disorders associated with deafferentation are higher than for other chronic pain conditions. Treatment is symptom-based, with evidence supporting first-line antineuropathic medications such as gabapentinoids and antidepressants. Studies examining noninvasive neuromodulation and virtual reality have yielded mixed results.

The functional and anatomical characterization of three spinal output pathways of the anterolateral tract

The nature of spinal output pathways that convey nociceptive information to the brain has been the subject of controversy. Here, we provide anatomical, molecular, and functional characterizations of two distinct anterolateral pathways: one, ascending in the lateral spinal cord, triggers nociceptive behaviors, and the other one, ascending in the ventral spinal cord, when inhibited, leads to sensorimotor deficits. Moreover, the lateral pathway consists of at least two subtypes. The first is a contralateral pathway that extends to the periaqueductal gray (PAG) and thalamus; the second is a bilateral pathway that projects to the bilateral parabrachial nucleus (PBN). Finally, we present evidence showing that activation of the contralateral pathway is sufficient for defensive behaviors such as running and freezing, whereas the bilateral pathway is sufficient for attending behaviors such as licking and guarding. This work offers insight into the complex organizational logic of the anterolateral system in the mouse.

Temporal Summation Predicts De Novo Contralateral Pain After Cordotomy in Patients With Refractory Cancer Pain

BACKGROUND

Percutaneous cervical cordotomy (PCC), which selectively interrupts ascending nociceptive pathways in the spinal cord, can mitigate severe refractory cancer pain. It has an impressive success rate, with most patients emerging pain-free. Aside from the usual complications of neurosurgical procedures, the risks of PCC include development of contralateral pain, which is less understood.

OBJECTIVE

To evaluate whether sensory and pain sensitivity, as measured by quantitative sensory testing (QST), are associated with PCC clinical outcomes.

METHODS

Fourteen palliative care cancer patients with severe chronic refractory pain limited mainly to one side of the body underwent comprehensive quantitative sensory testing assessment pre-PPC and post-PCC. They were also queried about maximal pain during the 24 h precordotomy (0-10 numerical pain scale).

RESULTS

All 14 patients reported reduced pain postcordotomy, with 7 reporting complete resolution. Four patients reported de novo contralateral pain. Reduced sensitivity in sensory and pain thresholds to heat and mechanical stimuli was recorded on the operated side (P = .028). Sensitivity to mechanical pressure increased on the unaffected side (P = .023), whereas other sensory thresholds were unchanged. The presurgical temporal summation values predicted postoperative contralateral pain (r = 0.582, P = .037).

CONCLUSION

The development of contralateral pain in patients postcordotomy for cancer pain might be due to central sensitization. Temporal summation could serve as a potential screening tool to identify those who are most likely at risk to develop contralateral pain. Analysis of PCC affords a unique opportunity to investigate how a specific lesion to the nociceptive system affects pain processes.

Cervical Cordotomy for Intractable Pain: Do Postoperative Imaging Features Correlate with Pain Outcomes and Mirror Pain?

BACKGROUND AND PURPOSE

Percutaneous cervical cordotomy offers relief of unilateral intractable oncologic pain. We aimed to find anatomic and postoperative imaging features that may correlate with clinical outcomes, including pain relief and postoperative contralateral pain.

MATERIALS AND METHODS

We prospectively followed 15 patients with cancer who underwent cervical cordotomy for intractable pain during 2018 and 2019 and underwent preoperative and up to 1-month postoperative cervical MR imaging. Lesion volume and diameter were measured on T2-weighted imaging and diffusion tensor imaging (DTI). Lesion mean diffusivity and fractional anisotropy values were extracted. Pain improvement up to 1 month after surgery was assessed by the Numeric Rating Scale and Brief Pain Inventory.

RESULTS

All patients reported pain relief from 8 (7-10) to 0 (0-4) immediately after surgery (P = .001), and 5 patients (33%) developed contralateral pain. The minimal percentages of the cord lesion volume required for pain relief were 10.0% on T2-weighted imaging and 6.2% on DTI. Smaller lesions on DWI correlated with pain improvement on the Brief Pain Inventory scale (r = 0.705, P = .023). Mean diffusivity and fractional anisotropy were significantly lower in the ablated tissue than contralateral nonlesioned tissue (P = .003 and P = .001, respectively), compatible with acute-phase tissue changes after injury. Minimal postoperative mean diffusivity values correlated with an improvement of Brief Pain Inventory severity scores (r = -0.821, P = .004). The average lesion mean diffusivity was lower among patients with postoperative contralateral pain (P = .037).

CONCLUSIONS

Although a minimal ablation size is required during cordotomy, larger lesions do not indicate better outcomes. DWI metrics changes represent tissue damage after ablation and may correlate with pain outcomes.

Neuroablative surgical treatments for pain due to cancer

Cancer pain is common and challenging to manage - it is estimated that approximately 30% of cancer patients have pain that is not adequately controlled by analgesia. This paper discusses safe and effective neuroablative treatment options for refractory cancer pain. Current management of cancer pain predominantly focuses on the use of medications, resulting in a relative loss of knowledge of these surgical techniques and the erosion of the skills required to perform them. Here, we review surgical methods of modulating various points of the neural axis with the aim to expand the knowledge base of those managing cancer pain. Integration of neuroablative approaches may lead to higher rates of pain relief, and the opportunity to dose reduce analgesic agents with potential deleterious side effects. With an ever-increasing population of cancer patients, it is essential that neurosurgeons maintain or train in these techniques in tandem with the oncological multi-disciplinary team.

Neurosurgical ablative procedures for intractable cancer pain

OBJECTIVE

Cancer patients suffering from severe refractory pain may benefit from targeted ablative neurosurgical procedures aimed to disconnect pain pathways in the spinal cord or the brain. These patients often present with a plethora of medical problems requiring careful consideration before surgical interventions. The authors present their experience at an interdisciplinary clinic aimed to facilitate appropriate patient selection for neurosurgical procedures, and the outcome of these interventions.

METHODS

This study was a retrospective review of all patients who underwent neurosurgical interventions for cancer pain in the authors' hospital between March 2015 and April 2018. All patients had advanced metastatic cancer with limited life expectancy and suffered from intractable oncological pain.

RESULTS

Sixty patients underwent surgery during the study period. Forty-three patients with localized pain underwent disconnection of the spinal pain pathways: 34 percutaneous-cervical and 5 open-thoracic cordotomies, 2 stereotactic mesencephalotomies, and 2 midline myelotomies. Thirty-nine of 42 patients (93%) who completed these procedures had excellent immediate postoperative pain relief. At 1 month the improvement was maintained in 30/36 patients (83%) available for follow-up. There was 1 case of hemiparesis.Twenty patients with diffuse pain underwent stereotactic cingulotomy. Nineteen of these patients reported substantial pain relief immediately after the operation. At 1 month good pain relief was maintained in 13/17 patients (76%) available for follow-up, and good pain relief was also found at 3 months in 7/11 patients (64%). There was no major morbidity or mortality.

CONCLUSIONS

With careful patient selection and tailoring of the appropriate procedure to the patient's pain syndrome, the authors' experience indicates that neurosurgical procedures are safe and effective in alleviating suffering in patients with intractable cancer pain.

Norepinephrine-induced downregulation of GLT-1 mRNA in rat astrocytes

AIM OF THE RESEARCH

Glutamate transporter-1 (GLT-1; also known as excitatory amino acid transporter 2) plays an important role in the maintenance of glutamate homeostasis in the synaptic cleft. Downregulation of GLT-1 in the spinal cord has been reported in chronic pain models, which suggests that GLT-1 is involved in the development of chronic pain. However, the mechanism by which GLT-1 is downregulated in the spinal cord is still unknown. We hypothesized that norepinephrine is involved in the regulation of GLT-1. The aim of this study was to investigate the effect of norepinephrine on GLT-1 expression in cultured astrocytes.

METHODS

This study involved both in vivo and in vitro experiments. We first validated changes in GLT-1 mRNA expression in the spinal cord of rats with spared nerve injury (SNI) using real-time RT-PCR. Next, cultured primary astrocytes from the rat spinal cord were stimulated with norepinephrine, and GLT-1 mRNA was subsequently quantitated. RNB cells, an astrocytic cell line, were also stimulated with norepinephrine and other α-adrenoceptor agonists.

RESULTS

SNI resulted in bilateral downregulation of GLT-1 in rat spinal cord. The in vitro study showed that norepinephrine and phenylephrine dose-dependently downregulated GLT-1 in primary astrocytes and RNB cells. Furthermore, the effect of norepinephrine was reversed by an α-adrenoceptor antagonist.

CONCLUSION

Norepinephrine downregulates GLT-1 mRNA expression in astrocytes via the α₁-adrenoceptor. Our results provide new insight into the mechanisms involved in downregulation of GLT-1 in the chronic pain models.

Usefulness of cordotomy in patients with cancer who experience bilateral pain: implications of increased pain and new pain

BACKGROUND:

Although mirror pain occurs after cordotomy in patients experiencing unilateral pain via a referred pain mechanism, no studies have examined whether this pain mechanism operates in patients who have bilateral pain.

OBJECTIVE:

To assess the usefulness of cordotomy for bilateral pain from the viewpoint of increased pain or new pain caused by a referred pain mechanism.

METHODS:

Twenty-six patients who underwent percutaneous cordotomy through C1-C2 for severe bilateral cancer pain in the lumbosacral nerve region were enrolled. Pain was dominant on 1 side in 23 patients, and pain was equally severe on both sides in 3 patients. Unilateral cordotomy was performed for the dominant side of pain, and bilateral cordotomy was performed for 13 patients in whom pain on the nondominant side developed or remained severe after cordotomy.

RESULTS:

After unilateral cordotomy, 19 patients (73.1%) exhibited increased pain, which for 14 patients was as severe as the original dominant pain. After bilateral cordotomy, 7 patients (53.4%) exhibited new pain, which was located cephalad to the region rendered analgesic by cordotomy and was better controlled than the original pain. No pathological organic causes of new pain were found in any patient, and evidence of a referred pain mechanism was found in 3 patients after bilateral cordotomy.

CONCLUSION:

These results show that a referred pain mechanism causes increased or new pain after cordotomy in patients with bilateral pain. Nevertheless, cordotomy can still be indicated for patients with bilateral pain because postoperative pain is better controlled than the original pain.

Microendoscopy-guided percutaneous cordotomy for intractable pain: case series of 24 patients

OBJECTIVE

The aim of this study was to show that microendoscopic guidance using a double-channel technique could be safely applied during percutaneous cordotomy and provides clear real-time visualization of the spinal cord and surrounding structures during the entire procedure.

METHODS

Twenty-four adult patients with intractable cancer pain were treated by microendoscopic-guided percutaneous radiofrequency (RF) cordotomy using the double-channel technique under local anesthesia. A percutaneous lateral puncture was performed initially under fluoroscopy guidance to localize the target. When the subarachnoid space was reached by the guiding cannula, the endoscope was inserted for visualization of the spinal cord and surrounding structures. After target visualization, a second needle was inserted to guide the RF electrode. Cordotomy was performed by a standard RF method.

RESULTS

The microendoscopic double-channel approach provided real-time visualization of the target in 91% of the cases. The other 9% of procedures were performed by the single-channel technique. Significant analgesia was achieved in over 90% of the cases. Two patients had transient ataxia that lasted for a few weeks until total recovery.

CONCLUSIONS

The use of percutaneous microendoscopic cordotomy with the double-channel technique is useful for specific manipulations of the spinal cord. It provides real-time visualization of the RF probe, thereby adding a degree of safety to the procedure.

Percutaneous computed tomography-guided radiofrequency ablation of upper spinal cord pain pathways for cancer-related pain

OBJECTIVE

The author presents data to support the continued need for ablative procedures, particularly cordotomy, in the management of cancer-related pain.

METHODS

Fifty-one patients with cancer-related body or face pain were treated with computed tomography-guided radiofrequency ablation of the spinothalamic tract or trigeminal tract nucleus in the upper cervical region of the spinal cord. Forty-one patients underwent a unilateral cervical cordotomy, and 10 patients underwent a trigeminal tractotomy-nucleotomy. Three methods to assess patient pain were used: degree of pain relief, Visual Analog Scale, and total sleeping hours. The Karnofsky scale was used to measure the patient's level of function pre- and postprocedure.

RESULTS

After surgical intervention, patients reported initial and 6-months follow-up pain relief as 98 and 80%, respectively.

CONCLUSION

Computed tomography-guided ablation of the upper cervical spinal cord is a safe and effective procedure to treat cancer pain involving the body or face. There remains a need for ablative procedures, in particular cordotomy, in the management of cancer-related pain.

Stereotactic bilateral anterior cingulotomy for intractable pain

To document the value of cingulotomy for pain relief, a series of 22 patients with medically intractable pain, including 15 with cancer pain and seven with non-cancer pain, underwent stereotactic bilateral anterior cingulotomy, between August 2001 and December 2002. Of the 15 patients with cancer pain, significant or meaningful pain relief was achieved in 67% of patients at one month follow-up, which decreased to 58% at three months and 50% at six months. Of the seven patients with intractable pain from non-neoplastic origin, four achieved significant pain relief, one obtained meaningful relief, and two reported no change at one year follow-up. There was no surgical mortality or permanent neurological morbidity. Two patients developed transient confusion and another two had mild gastrointestinal bleeding. No clinically evident personality or emotional changes were noted. However, subtle cognitive impairment, especially attentional deficits, were detected through detailed neuropsychological evaluation.

Continuous Intrathecal Meperidine for Severe Refractory Cancer Pain

The control of severe cancer pain may be problematic despite advances in pain management. Patients with severe intractable pain and/or intractable side effects may require aggressive interventional pain management strategies including the administration of medications by the continuous intrathecal route and/or neurosurgical procedures. Various medications, including opioids, local anesthetics, and alpha-2 agonists may be used intrathecally for the control of cancer pain. Failure of the intrathecal route may require the additional use of neurosurgical procedures such as cordotomy for pain control. We describe a case of severe cancer pain refractory to conventional intrathecal medications and cordotomy that was successfully managed by the addition of meperidine to the intrathecal regimen.