Spinal Cord Stimulation for Visceral Abdominal Pain

Published on 24/02/2015 by admin

Filed under Anesthesiology

Last modified 22/04/2025

Print this page

This article have been viewed 2403 times

Chapter 12 Spinal Cord Stimulation for Visceral Abdominal Pain

Leonardo Kapural

Chapter Overview

Chapter Synopsis: Visceral abdominal pain is among the many pain states that can be improved by electrical stimulation of the spinal cord (SCS). This chapter examines how SCS works to alleviate visceral pain, including considerations of the unique features of visceral pain transmission, which differ from somatic pain sensations. Spinal afferents from the viscera convey predominantly nociceptive (noxious) information, whereas vagal afferents carry information about the physiological state. Visceral pain is generally poorly localized and referred to somatic areas, although painful responses arising from different visceral organs vary. As in other indications, SCS is thought to relieve chronic visceral pain in several ways. Spinal gating of pain signals from small-fiber afferents may be decreased by continued stimulation of large-fiber, nonnociceptive afferents. Suppression of sympathetic efferents may also reduce the conditions leading to painful states, particularly ischemia. Because the underlying pathophysiology of visceral pain can vary dramatically among patients, it is crucial to determine proper electrode lead placement for implantation specific to the condition. Patient selection is of particular importance in treating visceral abdominal pain with SCS, and the treatment should be incorporated into a multidisciplinary plan.

Important Points:

Proper patient selection seems to provide better outcome of SCS for visceral abdominal pain.

Appropriately long trial of SCS is required to objectively assess patient’s improvements in pain and function.

Psychological evaluation and interdisciplinary committee for implantable devices assessment are now frequently required before conducting an SCS trial and are an essential part of the patient selection process.

Collaboration and consultation with the referring physician (frequently gastroenterologist) and continued exchange of information on implantation techniques should advance our understanding of mechanisms and refine this novel technique of SCS for abdominal visceral pain.

Clinical Pearls:

In most patients SCS leads are positioned with their tips at the level of the T5 vertebral body.

Midline position of the leads is most frequently used, and the number of leads used for trialing is not related to the success of the trial.

Retrograde differential epidural block can assist in proper selection of patients by identifying those who have predominantly visceral abdominal chronic pain.

Clinical Pitfalls:

On the basis of the currently available data, SCS for abdominal pain may be an exciting therapeutic option for patients with severe visceral pain. Food and Drug Administration (FDA) approval of the new indication for SCS is still required; that process should be initiated as soon as possible in the form of a randomized, prospective clinical trial.

Patients who require repeated magnetic resonance imaging (MRI) for ongoing monitoring of the disease process should not have SCS leads implanted.

Although there is no evidence that recurrent inflammatory acute pancreatitis episodes could be concealed with use of SCS, those painful episodes seem to respond poorly to such treatment.

Introduction

Abdominal pain is one of the most frequent complaints to a primary care physician, accounting for nearly 2.5 million office visits a year.¹ In many patients who present with abdominal pain, a definitive diagnosis can be made, but in 35% to 51% of patients, no identifiable cause is found.² There are approximately 2 million patients in the United States who currently experience severe abdominal pain. Most of them undergo a multitude of imaging studies and consultations with gastroenterology and surgery before being referred to a chronic pain specialist.^3,⁴ Despite adequate evaluations by multiple physicians, the etiology of some abdominal pain remains unknown.

Characteristics of visceral pain have been described extensively in literature as poorly localized, referred to somatic structures, and not evoked by all viscera.⁵ Visceral nociceptors are capable of responding to a variety of noxious stimuli such as mechanical and chemical stimuli. However, pain is not necessarily evoked from all of the viscera or from visceral injury. Some internal organs lack nociceptors and can be damaged without the individual perceiving pain. Spinal and vagal afferent fibers convey sensory information from the upper gastrointestinal tract to the central nervous system. Vagal afferents transmit predominantly physiological information, whereas spinal afferents transmit noxious information.⁶ The dorsal root ganglia of the spinal nerves contain cell bodies of both vagal and spinal afferents. Vagal afferents enter the brainstem, whereas spinal afferents enter the spinal cord, making synaptic connections with second-order neurons, thereby conveying visceral information to the central nervous system. The ascending spinal pathways project to the thalamic nuclei. Afferent fibers with visceral and somatic information converge onto spinothalamic and spinoreticular pathways.

The role of the dorsal column pathway in transmission/amplification of visceral pain has been described more recently by Palacek and Willis ⁷ and Palacek,⁸ and its role as participating in the neuromodulation of visceral painful information by spinal cord stimulation (SCS) has been hypothesized.⁹ Still the spinothalamic tracts are considered to be the major pathways for visceral nociception.¹⁰

Spinal sensitization process following tissue injury is characterized as a leftward shift in pain sensation/behavior (hyperalgesia) and enlargement of receptive fields within cutaneous areas able to activate the dorsal horn neuron (allodynia). This pattern is analogous to the change in functional bowel disorders, where a leftward shift in the stimulation-pain curve and enlargement of the somatic referral area occur.¹¹ The expansion of convergent cutaneous fields after repetitive distension of a viscus indicates the presence of a central mechanism contributing to the alteration of excitability of central neurons.¹² Brain-gut axis abnormalities can manifest as gastrointestinal motility and functional disorders. Because the neural activity plays a major role in these disorders, interventions aiming to modulate these processes can possibly improve the symptoms.

Spinal Cord Stimulation in Visceral Pain: Possible Mechanisms of Pain Relief

Several possible mechanisms may be involved in the phenomena of chronic abdominal pain relief produced by SCS. Published studies used the model of visceral hyperalgesia by colorectal distention in rats. Suppression of lumbosacral spinal neuron responses to the noxious colorectal stimuli by SCS could be produced by placing the electrical lead either near the lumbar or cervical dorsal column.^13,¹⁴ It was suggested that such suppression of the visceromotor reflex (VMR) by SCS may be the result of antidromic activation of primary efferent fibers within the dorsal column.^13,¹⁴ Spinal gating mechanisms¹⁵ might also be operant as an explanation for the reduction in pain transmission of small-diameter visceral fibers by stimulating large afferents using relatively low-intensity electrical stimulation.¹⁵

Although interruption of the recently described midline dorsal column pathway relieves visceral pelvic pain in cancer patients,^7,^8,^10,¹¹ at this time it is not clear if this visceral pathway can be modulated, excited, or suppressed by SCS.

Suppression of the sympathetic nervous system could play a significant role in control of the abdominal visceral pain;¹⁶ chemical or surgical neurectomy/sympathectomy involving the superior hypogastric or celiac plexus can suppress chronic abdominal pain.^16,¹⁷ Suppression of the sympathetic nervous system has been proposed as an important mechanism of pain control in intractable angina.¹⁸ It may be that such sympathectomy by SCS plays a role in suppression of chronic visceral abdominal pain.¹⁹

Clinical Experience in Using Spinal Cord Stimulation for Chronic Visceral Pain

Compelling data suggest that SCS may decrease pain and improve functional capacity in patients with various visceral chronic pain syndromes (Table 12-1). However, it may require years to accumulate sufficient clinical evidence.

Table 12-1: Reported Causes of Severe Chronic Abdominal Pain Treated with Spinal Cord Stimulation

Causes of Abdominal Pain Treated With SCS	Study/Case Series/Case Report	Number of Patients Studied
Mesenteric ischemia	Ceballos et al, 2000²⁰	1
Esophageal dysmotility	Jackson and Simpson, 2004²⁷	1
Irritable bowel syndrome	Krames and Mousad, 2005²¹	1
Chronic pancreatitis	Khan et al, 2005²²	5
Familial Mediterranean fever	Kapur, Mutagi, and Raphael, 2006²⁸	2
Pelvic visceral pain	Kapural et al, 2006¹⁹	6
Gastroparesis	Tiede et al, 2006²⁶	2
Chronic pancreatitis	Kapural and Rakic, 2008²³	1
Chronic pancreatitis	Kim et al, 2009²⁴	1
Chronic pancreatitis, abdominal adhesions, gastroparesis, mesenteric ischemia, postgastric bypass pain	Kapural et al, 2010²⁹	35
Chronic pancreatitis, postsurgical intraabdominal adhesion, gastroparesis	Kapural et al, 2010³⁰	76
Chronic pancreatitis	Kapural and Bensitel, 2010²⁵	30

SCS, Spinal cord stimulation.

The first case report on SCS for the treatment of abdominal pain described the case of a 78-year-old male with chronic, unrelieved severe postprandial pain caused by mesenteric ischemia. The patient experienced full pain relief after a SCS lead was placed epidurally at the T6 vertebral level.²⁰ The only case report dealing with irritable bowel syndrome (IBS) described a female patient who suffered from 11 to 14 diarrheal episodes per day and extreme pain from IBS and who, after placement of a thoracic SCS system, became immediately diarrhea free. However, her initial reduction in pain relief was not sustained.²¹

Khan, Raza, and Khan ²² described five successful cases of patients with nonalcoholic pancreatitis who received both single and dual leads placed at the T5-T7 vertebral height in the posterior epidural space. This report was followed by several others describing improvements in pain and function in patients with severe chronic pancreatitis²³^–²⁵ (see Table 12-1).

Tiede and associates ²⁶ described improvements in pain scores of patients with gastroparesis, whereas Jackson and Simpson²⁷ reported improved pain control and swallowing in a patient with a rather complicated history of esophageal problems. A most recently published report describes two cases of familial Mediterranean fever (FMF) in which painful abdominal intermittent attacks responded positively to SCS at T8-T9 and T7-T8, respectively.²⁸

Despite initial enthusiasm for a novel modality for treatment of severe abdominal pain, interpreting such limited published experience was further complicated by the fact that there was considerable variability in patient selection, lead positioning, and type of hardware used in these reports. Consequently, it remained unclear whether a reasonable fraction of the patients may have long-term benefit from stimulation.

Recently much larger clinical experience using SCS for treatment of chronic abdominal pain has been published.²⁹ In this study 35 patients were trialed with SCS over 4 to 14 days. Consistent with most previous reports (Figs. 12-1 and 12-2), SCS lead tips were positioned at T5 (n = 11) or T6 (n = 10) height within the epidural space. Thirty patients (86%) reported at least 50% pain relief on completion of the trial. Among 28 patients who received permanent implant, 19 were followed at least a year. Their visual analog scale (VAS) pain scores remained low (3.8 ± 1.9 cm; p < 0.001) at 1 year, as was opioid use (138.3 ± 134 to 38 ± 48 mg morphine equivalents [Fig. 12-3]). This report for the first time suggested that SCS may provide consistent long-term improvements as a very useful therapeutic option for patients with severe visceral pain.

Fig. 12-1 Fluoroscopic anterior-posterior (AP) radiographs of thoracic spine with appropriately positioned leads in midline and with the lead tips positioned anywhere from T4 (A) to T6 (C). Used were either 1, 2, or 3 leads (A,B,C, respectively) without significant difference in pain score improvements if one, two, or three leads were trialed.²⁹

(From Kapural L, et al: Spinal cord stimulation for visceral abdominal pain. Pain Med 11(3):347–355, 2010.)

Fig. 12-2 The graph illustrates the distribution of the leads’ tip position in 70 cases reported in a national survey. The most frequent positions of the tip of the spinal cord stimulation leads where the optimal paresthesias to cover the area of the patients’ pain was achieved were at T5 (26 patients) and T6 (15 patients) vertebral level.

(From Kapural L, et al: Spinal cord stimulation for visceral abdominal pain: results of the national survey. Pain Med 11(5):685-691, 2010.)

Fig. 12-3 The graph illustrates decrease in opioid use in 19 patients with spinal cord stimulation for chronic abdominal pain at 6 months and 1 year follow-up. Significant decrease of opioid use was achieved at 6 months and 1 year in these patients when compared to baseline (p = 0.089).

(From Kapural L, et al: Spinal Cord Stimulation for visceral abdominal pain. Pain Med 11(3):347–355, 2010.)

To initiate the formation of consensus between pain physicians on patient selection and technical aspects of SCS for abdominal visceral pain, a national survey directed to physicians who implant SCS for such pain was conducted recently and collected 76 case reports.³⁰ Considering so few cases reported by the physicians responding to this survey, SCS for abdominal visceral pain is still rarely used, despite possibly high therapeutic success rate. Causes for this include very few studies describing basic mechanisms of neuromodulation for long-standing visceral pain, comfort levels by the physicians, and issues with coverage of such treatment by the payers.

The technical aspects of SCS for the treatment of abdominal visceral pain seem to be uniform among physicians who use such technology across the United States and are also consistent with our larger retrospective study described previously.^29,³⁰ In most patients, the SCS leads were positioned with their tips at the level of the T5 (26 patients) or T6 vertebral body (15 patients) (see Fig. 12-2). Pain relief exceeded 50% in 66 of 70 patients reported. VAS pain scores before an implant were 8 ± 1.9 cm, whereas after the implant they were 2.49 ± 1.9 cm. The opioid use before an implant was 158 ± 160 mg; at the last office visit after the implant, it was 36 ± 49 mg. The weakness of this survey was that the subgroup of responding physicians may not adequately represent the population of all of the physicians who trialed SCS for chronic visceral abdominal pain but rather those who had largely positive results; therefore results may be biased. However, the aim was to examine technical aspects of SCS for chronic abdominal pain, and this was not an efficacy study.³⁰