Neurosurgery notes/Procedures/Cranial procedures/Functional cranial procedures/Management of pain/Spinal stimulation/Spinal cord stimulation

Spinal cord stimulation

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Spinal stimulation

General

  • Has superseded the technique known as dorsal column stimulation (DCS).
  • Pain relief with SCS can be achieved with ventral stimulation and is not reliant on stimulation-induced paresthesias as with DCS.
  • Pain relief can persist even after the cessation of stimulations, and is not reversed by naloxone.
  • The exact mechanism of action is undetermined.

Indications/contraindications

  • FDA approved indications include:
    • Relief of neuropathic leg pain
      • Most common use
    • Failed back surgery syndrome: especially if LE pain > back pain
    • Complex regional pain syndrome (reflex sympathetic dystrophy”)
  • Possible indications include:
    • Diabetic neuropathy
    • Refractory angina pectoris
    • Postthoracotomy pain (intercostal neuralgia)
    • Postherpetic neuralgia
    • Painful limb ischemia from inoperable peripheral vascular disease
    • Functional: spastic hemiparesis, dystonia, bladder dysfunction

Patient selection based on the

  • Cause of the pain,
  • Rigorous psychological evaluation,
  • Medical comorbidities, including
    • Opioid dependence
    • Risk of perioperative infection.

Relative CI

  • Cancer pain
  • Patients with limited life expectancy
  • Patients with untreated depression
  • Primarily nociceptive pain
  • Patients with polysubstance abuse
  • Patients with psychosis

Mechanism

  • Effective pain relief with SCS relies on the dorsal column stimulation-induced paresthesia overlapping the pain area.
  • Some anatomical pain distributions are known to be difficult to cover with SCS-induced paresthesias and/or may also induce additional, unwanted stimulation in non-pain areas.

Technique

  • The implant trial procedure is performed with the patient awake, under local anesthetic, to confirm appropriate stimulation coverage
    • Two techniques are used to place electrodes in the epidural space:
      • Wire-like electrodes placed percutaneously with a Tuohy needle.
      • “Paddle electrodes” placed via laminotomy
    • SCS leads have been placed anywhere:
      • Anatomical targets
            • C2-4
            Shoulder;
            C4-6
            Hand;
            T7-8
            Anterior aspect of the thigh;
            T8-9
            Low back region.
            T11-L1
            Posterior aspect of the thigh, leg, and perineum.
        • For angina
          • The active electrode poles are placed between C7 and T2,
          • Usually slightly to the left (the cardiac sensory afferents enter the cord at T1-5).
        • For peripheral artero-occlusive disease affecting the lower limb,
          • T10-11 has been the most commonly effective level.
      • Midline truncal stimulation between the neck and low back for pain is often difficult to achieve
      • Posterior column stimulation evokes tingling paresthesias targeted to overlay the area of pain and electrodes are always positioned in the dorsal epidural space
    • Leads placement
      • Usually inserted under fluoroscopic guidance in the midline;
      • However, if the symptoms are lateralized, leads can be placed eccentrically toward the affected side
      • Thoracic percutaneous leads are introduced into the epidural space via a Tuohy needle puncture at some level below the conus.
        • They are threaded rostrally until the desired coverage is achieved.
        • Wide distribution can be attained
        • Thoracic paddle leads are placed by performing a laminotomy at T9–10 with the lead passed rostrally to the T8–9 vertebral body level
      • Afferents enter the dorsal columns laterally and have lower activation thresholds than do the more medial, deeper fibers from lower segments.
        • To be most effective, the difference between the perception threshold for stimulation and the amplitude at which it becomes unpleasant (discomfort threshold) should be as large as possible so that consistent, comfortable stimulation can be achieved despite changes in posture.
        • The use of narrowly spaced electrode poles and guarded cathodes (i.e. a cathode surrounded by anodes) increases the chance of including “difficult” targets such as the low back area and perineum by permitting the recruitment of deeper and smaller fibers without “overstimulating” others.
    • Stimulation Fq
      • High fq
        • Paraesthesia independent
        • Central desensitization
        • Sti the dorsal horn/medial pain pathways
      • Low Fq
        • Paraesthesia dependent
        • Closing of the Gate in Gate theory
        • Sti posterior column
    • Trial
      • After electrode placement
      • External generator is used over several days to determine if there is a response.
      • Do for 1-2 weeks
      • Not all centers do it
      • Successful trial:
        • If there is greater than 50% pain reduction on visual analog scale (VAS).
          • Responders undergo subsequent conversion to a permanent system with internalization of an IPG
  • Implanted pulse generator (IPGs)
    • 2 types
      • Primary cell devices
      • Rechargeable
    • Are placed in a subcutaneous pocket in the
      • Flank,
      • Buttock,
      • Lower abdominal quadrant.
    • The IPG can be externally reprogrammed to “fine-tune” stimulation.

Complications

  • Overall risk of device-related complications is 32%.
  • Potential complications include:
    • Lead migration: 13%.
      • More common in percutaneous and cervical stimulators
    • Lead breakage: 9.1%
    • Infection: 3.5% incidence.
      • Treated with electrode and/or IPG removal and antibiotics
    • Hardware malfunction: 2.9%
    • Unwanted stimulation: 2.4%
    • Less common complications:
      • CSF leak,
      • Radicular pain,
      • Intermittent interference with cardiac pacemakers,
      • Neurologic deficit .

Outcome

  • Measure of success is
    • Primary goal
      • A sustained reduction in pain > 50%.
    • Secondary goals may include:
      • Improved health-related quality of life,
      • Reduction in pain medication requirement,
      • Increased functional capacity
      • Return to work.
  • In a retrospective report on 410 patients with SCS implantation for a variety of indications followed for a mean of 96 months, successful therapy was achieved in 74%

Specific syndromes treated

Persistent spinal pain syndrome/Failed back surgery syndrome (FBSS)
  • SCS improves pain control over either PT or medical management alone for FBSS.
  • At 24 months, SCS is as effective as reoperation in treating radicular pain, with no difference in ADLs or work status.
  • NICE guidelines 2008
    • Supportive of the cost-effectiveness of conventional SCS to manage FBSS patients in combination with a pain management programme if required
    • Indication
      • Adults with chronic pain of neuropathic origin who:
        • Continue to experience chronic pain (measuring at least 50 mm on a 0–100 mm visual analogue scale) for at least 6 months despite appropriate conventional medical management, AND
        • Who have had a successful trial of stimulation as part of the assessment
    • Contraindication
      • Adults with chronic pain of ischaemic origin except in the context of research as part of a clinical trial.
    • Trial prior to implantation
      • Advantages and disadvantages to a trial of SCS before proceeding to permanent implant (including false negative or false positive trial),
      • The trial lead should be left in place for a week to 10 days to assess whether or not SCS is beneficial for the patient (a successful trial results in pain reduction by more than 50% and increased function and quality of life).
      • The trial lead is then removed, while the patient awaits implantation of the permanent lead and internal pulse generator (IPG).
        • There is variation in practice, as some units will perform a trial for longer and complete the trial with connection of IPG, if the trial is successful.
        • The insertion of an IPG and connection to the epidural electrode is usually performed by the pain physician, although some centres collaborate with spinal surgeons, who insert the permanent implant.
  • Evidence
      • PROCESS trial (Prospective Randomized Controlled Multicenter Trial of the Effectiveness of Spinal Cord Stimulation):
      • N 100 FBSS patients
      • Treatment arms
        • SCS + conventional medical management (CMM) (n52) vs.
        • CMM alone (n48)
      • Inclusion criteria
        • >18 years or older
        • Suffering from predominant neuropathic pain of radicular origin in the legs (radiating in dermatomal segments L4 and/or L5 and/or S1) with or without associated less severe back pain were included.
        • The intensity of pain was at least 50 mm on a visual analogue scale for at least 6-months after at least one anatomically successful surgery for a herniated disc.
        • All patients had a documented history of nerve injury (i.e., root compression by herniated disc, compatible with the pain complaint).
        • The neuropathic nature of the pain was confirmed according to the routine clinical practice of each investigator and included mapping the pain distribution, examining sensory/motor/reflex changes.
      • Primary outcome
        • Improved leg pain at least >50mm on VAS
      • At 6 moths
        • SCS Had better QoL
        • SCS higher total health care cost 4x more than CMM
      • At 24-month
        • The primary outcome was achieved in
          • 37% of patients SCS + CMM Pts
          • 2% of patients CMM only
      • Patients were allowed to cross over. After crossover
        • The primary outcome is achieved in (P=0.02).
          • 47% of patients who had SCS plus CMM versus
          • 7% of patients (1 of 15) in the CMM
      In another randomized prospective study, patients with persistent or recurrent radicular pain
      • Inclusion
        • Post lumbosacral surgery
      • Arms
        • Reoperation
        • SCS.
      • Outcome
        • On an average of 3-year follow up, the SCS group required less opiate analgesics.
        • Of 19 patients in the SCS group compared to only 3 of 26 patients reoperated had self-reported pain relief and satisfaction (P < 0.01),
        • There was no difference in ADLs and work status.
        • Patients in the SCS group were less likely to crossover to undergo reoperation (5 of 24 patients from the SCS group versus 14 of 26 patients in the reoperation group, P= 0.02).21
      In a study evaluating the cost effectiveness of SCS, the initial cost of SCS is offset by future reductions in healthcare resource utilization. Taylor 2004
      • The medium to long term costs of SCS seem to be economically favorable compared to other therapies for FBSS.22
Complex regional pain syndrome
  • SCS may be effective for treating CRPS during the first couple of years, but no significant benefit was evident at 5-year follow-up.
  • CRPS is a chronic pain condition marked by continuous disabling intense aching or burning pain. Type I is nonspecific soft-tissue pain with no known nerve injury. Type II (p.501) follows a nerve injury. Spontaneous pain, hyperpathia and allodynia disproportionate to the inciting stimulus are hallmarks of CRPS. The pathophysiology leading to disproportional pain response is unknown and treatment options are limited.
  • In a randomized clinical trial
    • Patients with CRPS Type I were randomized to receive SCS plus physical therapy (PT) (36 patients) or PT alone (18 patients).
    • 24 of 36 patients had successful SCS trial and underwent implantation.
    • At 6 months, in the group that received SCS plus PT, pain intensity reduced by 2.4cm on the visual-analogue scale as opposed to an increase of 0.2cm in the PT only group (P < 0.001).
    • In addition, 39% of patients in the SCS group had “much improved” globally perceived effect vs. 6% (P=0.01).
    • The health-related quality of life only improved in the SCS group.
    • At 2-year follow-up, pain intensity in the SCS group reduced by 2.1 vs. 0.0cm in the PT group compared to baseline (P < 0.001) and global perceived effect was “much improved” in 43% vs. 6% (P = 0.001).24
    • However, these benefits were no longer significant in 5 years.
Peripheral vascular disease
  • SCS does help with pain due to inoperable limb ischemia
  • It may or may not improve healing of pressure ulcers.
  • A review of six controlled studies of nearly 450 patients, SCS+ medical treatment VS medical treatment alone.
    • Although there was no significant difference in ulcer healing,
    • The use of analgesics was less
    • Limb salvage after 12 months was significantly higher in the SCS group (relative risk = 0.71)
Angina pectoris
  • SCS was as effective as CABG in controlling refractory angina and protecting against MIs.
    • Due to
      • Increase in blood flow.
      • Redistribution of local blood flow
  • SCS improves exercise capacity by an unknown mechanism.
  • In a prospective study of 104 patients who underwent SCS placement for refractory angina pectoris (average follow-up ≈ 13 months),
    • 73% had>50% reduction of weekly anginal episodes compared to baseline.
Diabetic neuropathy
  • SCS to aid with refractory pain from diabetic neuropathy.
  • Further study is needed.
  • No good clinical data are available. A few studies with small numbers of patients suggest SCS can provide significant pain relieve in most patients with diabetic neuropathy who have failed conservative management.
  • A small prospective, open-label study reported 9 of 11 patients with diabetic neuropathy that failed conservative treatment. At 6 months.
    • Pain score on visual analogue scale decreased from 77 to 34.
    • Microcirculatory perfusion did not change significantly from baseline