Interventional Approaches to Chronic Pain: Blocks, Stimulators, Pumps

1. Interventional Approachesto Chronic Pain:Blocks, Stimulators, Pumps

2. 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

3. 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

4. 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)

5. 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

6. 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

7. 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

8. 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.

9. 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.

10. 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)

11. 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

12. 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

13. 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)

14. 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.

15. 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.

16. 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

17. Layering of Contrast in Epidural Space (C5-6 Epidural)

18. 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

19. C 3-4 Facet Injection (Lateral View)

20. S1 Root Block (Trans-Sacral)

21. 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

22. Lumbar Sympathetic Block (Lateral View)

23. 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

24. Celiac Block (Lateral View)

25. CT-Guided Celiac Block

26. 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)

27. 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…

28. 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…

29. 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

30. 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.

31. “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.

32. 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

33. 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?

34. 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.

35. 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

36. 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

37. 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)

38. 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