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Interventional Approaches to Chronic Pain: Blocks, Stimulators, Pumps

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Interventional Approaches to Chronic Pain: Blocks, Stimulators, Pumps. Background. Neurosurgical ablative treatments for pain since 19th century but now infrequently used Ablation eclipsed by percutaneous injections or therapies that target central or peripheral pathways Nerve blocks

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background
Background
  • Neurosurgical ablative treatments for pain since 19th century but now infrequently used
  • Ablation eclipsed by percutaneous injections or therapies that target central or peripheral pathways
    • Nerve blocks
    • Spinal stimulation
    • Pumps
nerve blocks i
Nerve Blocks (I)
  • Diagnostic: local anesthetic only, to clarify mechanism or simulate effects of therapy
  • Therapeutic: anesthetize a site or pathway temporarily (local anesthetic) or “permanently” (lytic agent), or reduce inflammation (corticosteroid)
  • A block may be both diagnostic and therapeutic, eg, sympathetic block or trigger-point injection
nerve blocks ii
Nerve Blocks (II)
  • Common blocks for chronic pain include
    • Trigger-point injection
    • Tourniquet or Bier block
    • Peripheral nerve injection (eg, ilioinguinal, lateral femoral cutaneous, greater occipital)
    • Paravertebral (nerve root) injection
    • Epidural injection
    • Intra-articular (eg, facet, SI) injection
    • Sympathetic block (cervical, lumbar)
    • Plexus block (celiac, hypogastric)
nerve blocks iii
Nerve Blocks (III)
  • Case reports, preclinical data support long-lasting effects of local anesthetic blockade
    • RCTs support lytic celiac block
  • However, unclear how much clinical improvement reflects placebo effects, irrelevant cues, systemic absorption of local anesthetic, expectations
  • Side effects possible
  • Rarely successful as a “stand-alone” strategy for chronic pain
trigger point injection i
Trigger-Point Injection I
  • Essential criteria
    • Taut band palpable (if muscle accessible)
    • Exquisite spot tenderness of a nodule in a taut band
    • Pressure on tender nodule reproduces pain
    • Range of motion with stretch limited by pain
  • Confirmatory observations
    • Visual or tactile identification of local twitch response
    • Local twitch response on needling tender nodule
    • Pain/hyperesthesia in recognized pattern
    • Activity in tender nodule on EMG
trigger point injection ii
Trigger-Point Injection II
  • Trigger points may refer pain
    • Toward the periphery (eg, suboccipital, infraspinatus)
    • Proximally or medially (eg, biceps brachii)
    • Locally (eg, serratus posterior inferior)
  • Techniques
    • Needle only (no injection)
    • Local anesthetic only
    • Local anesthetic + glucocorticoid (evidence?)
    • Botulinum toxin type A
trigger point injection iii
Trigger-Point Injection III

Reproduced with permission from Simons DG, et al. Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual. Vol. 1. 2nd ed. Philadelphia, Pa: Williams & Wilkins; 1999:160.

trigger point injection iii1
Trigger-Point Injection III

Reproduced with permission from Simons DG, et al. Travell & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual. Vol. 1. 2nd ed. Philadelphia, Pa: Williams & Wilkins; 1999:159.

tourniquet or bier block
Tourniquet or Bier Block
  • Facilitates mobilization of upper or lower extremity in known or suspected CRPS
  • Same technique for sympathetically-maintained versus sympathetic-independent pain
  • Many variants: all use IV cannulation, drainage of blood (gravity, Esmarch’s bandage), proximal tourniquet (eg, systolic BP + 100), slow release after ~20 min
  • Medications: local anesthetic, many others (sympatholytic, anti-inflammatory)
peripheral nerve injection
Peripheral Nerve Injection
  • Spontaneous entrapment syndromes
    • Greater occipital (occipital neuralgia)
    • Lateral femoral cutaneous (meralgia paresthetica)
    • Ilioinguinal
  • Post-incisional or post-traumatic neuroma
    • Cranial (post-craniotomy)
    • Intercostal (post-thoracotomy)
    • Abdominal wall (trochar sites)
    • Herniorrhaphy
  • Local anesthetic + glucocorticoid
paravertebral nerve root injection
Paravertebral (Nerve Root) Injection
  • Diagnostic
    • Establish or confirm anatomic mechanism of pain (eg, atypical dermatomal distribution in disk disease or multilevel foraminal stenosis)
  • Therapeutic
    • Deposit local anesthetic plus glucocorticoid via paravertebral and/or transforaminal approach
  • Technique
    • Fluoroscopy or CT essential to validate, document needle placement
    • Radiopaque contrast outlines/tracks root
epidural injection i
Epidural Injection (I)
  • Employed for decades using various techniques, materials, and patients
    • Poor documentation of diagnosis, pain, technique, outcomes
  • Limited RCT evidence of efficacy in subpopulations, but most reports are case series
  • Techniques (glucocorticoid + local anesthesic)
    • Translaminar
    • Transforaminal
    • Caudal (useful if prior lumbar surgery, scarring)
slide14

Trans-Ligamental Injection

Reproduced with permission from Covino BG, Scott DB. Handbook of Epidural Anaesthesia and Analgesia. New York, NY: Grune & Stratton, Inc; 1985:90.

slide15

Sacral Extradural Injection

Reproduced with permission from Eriksson E, ed. Illustrated Handbook in Local Anaesthesia. 2nd ed. London, Eng: Lloyd-Luke (Medical Books) Ltd; 1979:135.

epidural injection ii
Epidural Injection (II)
  • Applied for symptomatic relief in
    • Disk protrusion with radiculopathy
    • Spinal stenosis (circumferential or foraminal)
    • Acute pain, local inflammation of vertebral fracture ( subsequent vertebroplasty)
    • ? Acute herpes zoster, using local anesthetic alone
  • May facilitate rehabilitation, avert surgery when applied within multidisciplinary framework
intra articular injection
Intra-Articular Injection
  • Facet, large joints, sacroiliac most common
  • Diagnostic
    • Clarify clinical impression of a “facet syndrome” or “SI joint pain”
    • (Facet:) simulate results of potential spinal fusion or denervation of medial branch of dorsal ramus
  • Therapeutic (local anesthetic + glucocorticoid)
    • Reduce inflammation, pain
    • Increase mobility, facilitate rehabilitation
  • Controversy as to efficacy and effectiveness
sympathetic block
Sympathetic Block
  • Diagnostic
    • Superior cervical (“stellate”) ganglion
    • Lumbar
    • Note need for (but insurers’ reluctance to pay for) placebo controls
  • Therapeutic
    • CRPS of upper, lower extremity
    • Facial neuralgias
  • Technique
    • Local anesthetic
    • Neurolytic
plexus block celiac hypogastric
Plexus Block (Celiac, Hypogastric)
  • Visceral nociceptive afferent pathways are heterogeneous: sympathetic (eg, celiac), parasympathetic (eg, hypogastric)
  • Meta-analysis indicates efficacy of celiac block for abdominal cancer pain, but case series show little benefit (<10%) in chronic pancreatitis
  • Case series of hypogastric block for perineal pain
  • Technique
    • Fluoroscopy or CT essential for safety, documentation
    • Reversible block with local anesthetic
    • Neurolysis with alcohol, phenol
spinal cord stimulation
Spinal Cord Stimulation
  • Background: peripheral electrical stimulation for pain control since prehistory; recent “gate theory”
  • Retrospective, uncontrolled case series show that SCS can reduce intensity of neuropathic pain
  • Biases in existing literature (lack of blinding, heterogeneity of interventions/assessments, small numbers) confound its interpretation
  • Recent 6-month RCT: “with careful selection of patients and successful test stimulation, SCS is safe, reduces pain and improves HRQOL in chronic RSD” (Kemler MA, et al. N Engl J Med. 2000; N = 36)
possible risks scs or pump
Possible Risks (SCS or Pump)
  • Non-specific: electrical, mechanical (migration, separation of electrode or catheter) failure
  • Route-specific: infection, fibrosis, extrusion
  • Drug-specific (pump): neurotoxicity, sedation, constipation, hypotension…
  • For opioids (pump): constipation, urinary retention, nausea, impotence, nightmares, pruritus, edema, sweating, fatigue…
implanted pumps for pain
Implanted Pumps for Pain
  • Spinal anesthesia ~100 y
  • Selective spinal opioid analgesia ~25 y
  • Early chronic use of opioid PCEA supplanted by intrathecal cannulation
  • Single agents: opioids, local anesthetics, NSAIDs, clonidine, cholinomimetics, calcium channel blockers, GABA-A and -B, peptides, NMDA antagonists, adenosine
  • Combinations: opioid-opioid, opioid-local anesthetic, morphine-clonidine…
theoretical benefits of it rx i
Theoretical Benefits of IT Rx (I)
  • “Targeting” offers dosage reductions
  • Only route possible for certain drugs
  • Fewer side effects from decreased and spatially restricted dosage
  • Greater efficacy from targeted, higher concentrations (eg, in neuropathic pain) and locally applied combinations
theoretical benefits of it rx ii
Theoretical Benefits of IT Rx (II)
  • Nociceptive activity provokes persistent functional and morphologic changes
  • Pain, especially chronic pain, is a disease
  • Spinal analgesic therapy = “dorsal horn amnesia”*
  • “Combination analgesic chemotherapy”*

*See Carr DB, Cousins MJ. Spinal route of analgesia. Opioids and future options. In: Neural Blockade in Clinical Anesthesia and Management of Pain. 3rd ed. Philadelphia, Pa: Lippincott-Raven; 1998:915-983.

algogenic neuropoiesis
“Algogenic Neuropoiesis”
  • Transformation of neuronal morphology and function as the result of nociception*
  • “Poiesis” = organized creation, growth
  • A highly organized process (Ca++, second messengers, oxidative stress, novel gene expression, growth factors, apoptosis)

*See Walker S, et al. Anesth Analg. In press.

it analgesia evidence
IT Analgesia: Evidence
  • Abundant preclinical proof of IT analgesia using various agents, singly or in combination
  • Narrative reviews from 1980s–1990s summarize clinical effectiveness and conclude IT analgesia generally is safe, well-tolerated, effective for acute or chronic cancer and noncancer pain
it evidence limitations i
IT Evidence: Limitations (I)
  • Level 5 clinical evidence (uncontrolled case reports/series)—like >90% of all pain literature
  • Inclusion based upon failure of prior therapy but unclear whether/how therapy optimized
  • Nonuniform or unknown Dx, pain/QOL scores
  • Side effects vs effects: “different dimensions”
  • Limited psychologic, toxicologic data
  • Effect of drug redistribution?
it evidence limitations ii
IT Evidence: Limitations (II)
  • No controls = UNDEFINABLE relative efficacy!
  • Without data on relative efficacy, algorithms/guidelines follow “practice-based evidence”
  • For evidence-based practice, RCTs or CCTs are necessary to control for expectations, psychosocial and placebo/nocebo effects
  • “Consort” statement needed for pain trials
  • “Need for additional large published controlled studies… highlighted” by review of Bennett et al*

*See Bennett G, et al. J Pain Symptom Manage. 2000;20:S37-S43.

intrathecal opioids prospects
Intrathecal Opioids: Prospects
  • Opportunity for translational research on “dorsal horn amnesia”
  • Need for uniformity, control groups
  • Requirement for appropriately powered trials: “size does matter”
  • Control for drug interactions
  • Long-term follow-up
  • Clinical consensus drives initial opioid use alone, but may be better to start with combinations
prudent practice
Prudent Practice
  • Any nerve block, no matter how deftly and carefully performed, can lead to sudden complications related to intraneural, intraspinal, or intravascular injection
  • Anyone who considers performing a nerve block should provide monitoring, vigilance during and afterwards, and resources for prompt resuscitation
a thought
A Thought
  • Interventional approaches often are reserved for patients with well-established problems, failure of other Rx, and pronounced disability
  • Do we miss an opportunity for early, cost-effective preventive treatment by reserving interventions for those least likely to benefit?
  • Established neuropoiesis, entrenched pain behavior, proven self-advocacy in disabled role may explain data on low likelihood of return to work
  • “Youth is a wonderful thing; what a crime to waste it on children” (George Bernard Shaw)
conclusions
Conclusions
  • Best to reserve blocks, other invasive Rx for when other modalities fail?
  • Substantial risks and benefits of SCS, IT Rx
  • Stand-alone interventions less likely to succeed than multidisciplinary ones
  • Irresistible force (evidence-based medicine) now is meeting immovable object (case reports, customary practice)
  • Needed: outcomes data on effectiveness and large RCTs re: efficacy
ad