Samuel Samuel MD
Salim Hayek MD, PhD
Michael Stanton-Hicks MB, BS
Interventional nerve blocks remain the mainstay treatment of chronic pain despite advances in pharmacologic and nonpharmacologic modalities. However, multiple factors (including social, emotional, financial, and legal issues) further compound the complexityofchronic pain, necessitating a multidisciplinary approach to its management. Such a discussion is beyond the scope of this chapter, which will primarily focus on interventional nerve blocks for chronic pain conditions and when the primary care physician should refer patients for these procedures. Some aspects of the techniques are described to assist the internist in determining whether a patient might tolerate the procedure. Although the internist is unlikely to be performing these techniques, it is important to understand the goals of the procedures, the potential benefits, and the possible complications.
While diagnostic regional anesthetic procedures have been applied to practically every peripheral and cranial nerve, in the interest of demonstrating that by its interruption either somatosensory, visceromotor, or sudomotor efferents abolish or change the described pain, it is probably the systematic blocking of the axial spine and sympathetic blocks that have the greatest usefulness in clinical diagnosis of chronic pain conditions.
Interventional nerve blocks can be broadly classified into three types: diagnostic blocks, prognostic blocks, and therapeutic blocks. Prognostic blocks are conducted to predict the efficacy of a neurodestructive procedure (to prevent a potentially unnecessary operation). Prognostic blocks also temporarily provide patients the sensations of a more definitive procedure, thereby allowing them to determine whether the resulting numbness might be tolerable to them.
The use of blocks for diagnosis and prognosis depends on an assumption of anatomic consistency. Nerve structures are expected to be found in predictable places and to have predictable connections, but there are important limitations to these assumptions, with most anatomic parameters showing normal variance. There is 50% accuracy in guessing vertebral level for needle placement without fluoroscopy and for this reason most nerve block techniques have no validity unless conducted under fluoroscopic guidance. The use of a high-resolution C-arm image intensifier with associated computerized image generation is considered to be essential if the results are to contribute to both diagnosis and definitive therapeutic maneuvers.
Nerve blocks are used for diagnosis and treatment of multiple pain syndromes, including low back pain, headache, abdominal pain, failed backsurgery syndrome, post-thoracotomy pain syndrome, postherpetic neuralgia, myofascial pain syndrome, pain secondary to malignancy, compression fractures, complex regional pain syndrome (CRPS) type I and type II, whiplash injuries, pain originating from vascular insufficiency, diabetic neuropathy, and the diagnosis of central pain syndrome.
Selective Nerve Root Sheath Injection
Chronic back pain, radiculopathies, and their associated disabilities represent a significant health problem. At some time in life, 70 to 85% of all people have back
pain, with an annual prevalence ranging from 15 to 45%. Symptoms are most common in middle-aged adults, with back pain equally common in men and women. Back pain is the most frequent reason for activity limitation in persons younger than 45 years of age, the second leading reason for doctor visits and absenteeism from work, and the third common cause for surgical interventions.
The primary site of back pain is the lower back in 85% of back pain sufferers. Annually, about 2% of the work force has back injuries covered by the Bureau of Workers Compensation. The total annual direct cost of treating this subgroup of patients rose from $4.6 billion in 1977 to $11.4 billion in 1994. From 1979 to 1990, rates of back surgery in the United States increased dramatically; the increase in surgical rates was especially marked for spinal fusions.
Back pain associated with radiculopathy is the main indication for selective nerve sheath injection, since the contribution of root inflammation to pain may not be certain or the level of the lesion may be unclear.
Computed tomography (CT) or magnetic resonance imaging (MRI) and electrophysiologic evaluation by electromyography may be inconsistent or may be inconclusive. Abnormal imaging findings in asymptomatic persons (prevalence as high as 40%) demonstrates the inability of abnormal anatomy to indicate a pain source. A further cause of confusion is the presence of disease at multiple levels, because the origin of pain may be any one site or a combination of sites. Finally, evaluation is especially difficult after laminectomy because imaging is impeded by the presence of hardware or the presence of scar tissue in the epidural space.
Duration of Benefit
In diagnostic blocks, the duration of the block essentially reflects the duration of action of the local anesthetic used (short, intermediate, or long-acting). Therapeutic benefit from the block is variable, with multiple confounding variables involved; however, the average success rate after 12 months of follow-up is approximately 75-80% in patients with disk abnormality.
When used therapeutically, a mixture of local anesthetic and corticosteroid is used. Corticosteroids decrease pain due to inflammation and sensitization of nerve fibers through their anti-inflammatory action and the release of phospholipase A2 inhibitor. Corticosteroids also block nociceptive input, block the transmission in C fibers but not in A β fibers and inhibit the formation of adhesion and fibrosis.
The following are possible complications due to selective nerve root sheath injection:
Stanton-Hicks M. Nerve blocks in chronic pain therapy-are there any indications left? Acta Anaesthesiol Scand. 2001;45:1100.
Differential Epidural Block
When the location of pain makes diagnosis difficult (as in abdominal pain), differential nerve blocks can be valuable in providing the information necessary to verify a certain diagnosis and delineate a treatment plan. The test relies on the selective differential blockade of one structure, without blocking others, using specific concentration of local anesthetic and saline. The three classes of nerve fibers are as follows:
The test can be carried out using epidural, spinal anesthesia, or peripheral nerve plexus blocks and interpreted in an antegrade or retrograde fashion. In the antegrade approach, the clinician observes the gradual onset of analgesia with increasing doses of local anesthetics injected, whereas in the retrograde approach, after analgesia is achieved with a large bolus, the clinician observes the relationship between the block wearing off and the gradual return of pain. For instance, in cases of visceral abdominal pain, pain is abolished first in the antegrade approach and its relief outlasts the duration of local anesthesia in the retrograde approach. Musculoskeletal pain, on the other hand, returns as soon as dermatomal anesthesia is resolved.
Two shortcomings of this technique are that (1) the differential nerve blocks can be very time consuming and (2) occasionally, no clear-cut end points are obtained, with overlap of results making interpretation of the test difficult.
The following are possible complications of a differential epidural block:
Zygapophyseal Joint Injection (Facet Joint Injection)
The zygapophyseal (facet) joints are paired diarthrodial joints between the posterior elements of the adjacent vertebrae that can contribute drastically to the problem of low back pain. The percentage of all patients with low backpain who have a significant proportion of their pain attributable to the facet joint varies from 15 to 50% in published series.
Injection of a small amount of local anesthetic into the facet joint (0.5 mL, 0.75% bupivacaine) or interruption of the median branch nerves to the facet joints are standardized techniques for the diagnosis of zygapophyseal joint-symptoms. Because each joint is innervated by at least two medial branches, two adjacent levels should always be blocked.
Table 4-1 shows a scoring system that was developed to determine which patients will benefit from facet joint injection. Patients with a score of 60 points or higher had 100% prolonged response from a facet joint injection. A score of 40 points or higher predicted 78% prolonged response.
Table 4-1. Scorecard for Probability of Pain Relief with Facet Joint Injection.
Duration of Benefit
The duration of pain relief in diagnostic blocks probably reflects the duration of the local anesthetic used. Patients with consistent pain relief with such a block but of short duration may benefit from radiofrequency ablation of the median branch block with reported duration of up to 1 year. Another alternative to radiofrequency lesioning is pulsed radiofrequency, with reported duration of 4 months and decreased incidence of complications compared with radiofrequency ablation.
Unless there are localizing signs, the L4-5, L5-S1 are the most affected joints. The block is performed under fluoroscopy with the patient in the prone position and a pillow placed under the lower abdomen. After the back is prepared and draped, the facet joint or the junction of the transverse process with the facet joint (in case of median branch block) is identified. Using a 22-gauge spinal needle, the needle is introduced and a mixture of 0.5 mL of 0.75% bupivacaine and 20 mg of triamcinolone is injected into each of the designated joint or median branch.
Although rare, complications may include infection, transient radicular pain, subarachnoid injection, backache, muscle spasm, allergic reaction, joint rupture and necrosis in case of intra-articular injection, and neuritis in the case of radiofrequency ablation.
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Saal JS. General principles of diagnostic testing as related to painful lumbar spine disorders: a critical appraisal of current diagnostic techniques. Spine.2002;27:2538.
Cervical facet joint has been shown to be the most commonly involved structure following neck injury, especially in whiplash injury. This injury represents 1 of the major causes of neck pain with an estimated incidence of 4 per 1000 population. An estimated 42% of whiplash injuries become chronic, with pain persisting in about 10% of the cases; it may also result from twisted neck and poor sleep postures.
Chronic neck pain represents about 30% of the chronic pain conditions, with a staggering impact on US society; an estimated annual cost of about $90 billion is split between treatment and work losses. This economic impact reflects the importance of recognizing and promptly treating conditions that lead to chronic neck pain.
Cervical facet joints and its innervations are slightly different than the lumbar facet joints. The atlanto-occipital (C0-1) and the atlantoaxial (C1-2) are innervated by C1 and C2 ventral rami and not the dorsal primary ramus; hence, the intra-articular injection is the only way to block these joints. Cervical facet joints from C3-T1 are supplied by medial branches of the dorsal rami above and at the same level as the joint, so either intra-articular or median branch block could be used for diagnostic or therapeutic purposes. Table 4-2 describes the distribution of pain of cervical facet joint origin.
Patients with cervicogenic headaches may benefit from facet joint medial branch block since the third occipital nerve (dorsal ramus C3) has a close anatomic proximity to and innervates the C2-3 zygapophyseal joint. This joint and the third occipital nerve appear most vulnerable to trauma from acceleration-deceleration (“whiplash”)
injuries of the neck. Pain from the C2-C3 zygapophyseal joint is referred to the occipital region but is also referred to the frontotemporal and periorbital regions.
Table 4-2. Distribution of Pain of Cervical Facet Joint Origin.
Duration of Benefit
Despite the wide variability in the duration of pain relief with cervical facet injection, some reports cite pain relief and improved range of motion for up to 12 months. In conjunction with the facet injection, other adjuvant treatment includes traction, local heat, manipulation with correction of facet subluxation, and medical treatment with nonsteroidal anti-inflammatory drugs (NSAIDs).
With the patient lying prone (some clinicians advocate a lateral or even a supine position with easier accessibility to the airway), the posterior neck is prepared and draped. Under fluoroscopic guidance, a 22-gauge spinal needle is inserted at the desired levels to be blocked; the importance of slow advancement of the needle with serial anteroposterior and lateral fluoroscopic imaging for correct needle placement and direction must be emphasized. After negative aspiration (close proximity of the vertebral artery), 0.5 mL of 0.75% bupivacaine and 20 mg of tri-amcinolone is injected.
In addition to the complications of the lumbar facet blocks, complications related to the cervical facet injection include epidural and intrathecal injection progressing to total spinal anesthesia, intravascular injection, and seizures.
Bogduk N et al. Biomechanics of the cervical spine Part 3: minor injuries. Clin Biomech (Bristol, Avon). 2001;16:267.
Freeman MD et al. A review and methodologic critique of the literature refuting whiplash syndrome. Spine. 1999;24:86.
Kwan O et al. A review and methodologic critique of the literature supporting ‘chronic whiplash injury’: part I-research articles. Med Sci Monit. 2003;9:RA203.
Peloso P et al; Cervical Overview Group. Medicinal and injection therapies for mechanical neck disorders. Cochrane Database System Rev. 2005;(2):CD000319.
Siegmund GP et al. Mechanical evidence of cervical facet capsule injury during whiplash: a cadaveric study using combined shear, compression, and extension loading. Spine. 2001;26:2095.
Discography can be considered as a purely diagnostic modality for the diagnosis of back pain. Discography is only indicated to rule out or to rule in discogenic pain with concordant or nonconcordant pain in the suspected degenerated disk.
For diagnostic purposes, MRI is sensitive in detecting disk abnormalities, yet MRI is capable of detecting degenerated, desiccated disks. Therefore, discography is considered the gold standard and an invaluable adjunct for the diagnosis of discogenic pain.
Indications for discography include, but are not limited to, the following:
While the specificity may range from 20 to 90% depending on patient selection, discography results should be carefully validated and the procedure should be performed by an experienced clinician. Most clinicians will perform discography on two consecutive disks.
After placing the patient in a prone position, a postero-lateral extraspinal approach with fluoroscopic guidance to the desired disks is used. The skin is prepared and draped. The C-arm is then obliquely rotated until the facet joint “shadow” projects to about the middle of the vertebral body. A 22- or 25-gauge 6-inch needle with introducer is inserted, until it reaches the inner third of the disk. Upon confirmation of needle position using a true anteroposterior and lateral pictures, 0.5-1.5 mL of water-soluble radio-opaque contrast material is injected. The patient's response, the distribution of the dye, resistance, and volume injected are all noted and recorded.
A normal disk accommodates between 0.5 mL and 1.5 mL of contrast material; in the case of a fissured disk, there will be a path of least resistance with an increase in the capacitance of the disk and apparent abnormal spread of the contrast. However, these findings should be accompanied by concordant pain to label this study as a positive provocative discography.
Discitis represents one of the most devastating complications of discography. Thus, discography requires a surgically sterile environment with extreme caution when entering the disk, and despite lack of data to support the use of prophylactic antibiotics, most clinicians do provide a dose of antibiotics prior to the procedure.
Nausea, convulsions, and severe back pain during the procedure may occur. Meningitis, spinal headache, sub-dural or epidural abscess, intrathecal hemorrhage, arachnoiditis, nerve root injury, paravertebral muscle pain and contusions, postprocedural pain exacerbation, vasovagal reactions, allergic reactions, and damage to the disk including but not limited to herniation are other possible complications.
Anderson MW. Lumbar discography: an update. Semin Roentgenol. 2004;39:52.
Olmarker K et al. Selective inhibition of tumor necrosis factor-alpha prevents nucleus pulposus-induced thrombus formation, intra-neural edema, and reduction of nerve conduction velocity: possible implications for future pharmacologic treatment strategies of sciatica. Spine. 2001;26:863.
Willems PC et al. Lumbar discography: should we use prophylactic antibiotics? A study of 435 consecutive discograms and a systematic review of the literature. J Spinal Disord Tech. 2004;17:243.
Selective Sympathetic Blocks
Selective sympathetic blockade interrupts the efferent sympathetic fibers that are sometimes pathologically involved in a number of medical conditions, including CRPS, neuropathic pain (mononeuropathy, plexopathy), cranial neuralgia, hyperhidrosis, and many other conditions. Surgical or chemical sympathectomy is used to manage a variety of syndromes, yet relief following sympathetic blockade is not consistent, and relapses are common.
The cervical sympathetic trunk contains three ganglia: the superior, middle, and inferior cervical ganglia. In 80% of the population, the lowest cervical ganglia is fused with the upper thoracic ganglion to form the cervicothoracic ganglion. The cervicothoracic ganglion lies on or just lateral to the longus colli muscle between the base of the seventh cervical transverse process and the neck of the first rib. The cervicothoracic ganglion receives preganglionic fibers from the lateral gray column of the spinal cord. The preganglionic fibers for the head and neck emerge from the upper five thoracic spinal nerves, ascending in the sympathetic trunk to synapse in the cervical ganglion. The preganglionic fibers supplying the upper extremity originate from the upper thoracic segment between T2-T6, which in turn synapses in the cervicothoracic ganglion. The paradox of accepting Horner syndrome as a gold standard for sympatholysis of the upper extremity is still widely accepted; yet, the presence of Horner syndrome does not indicate complete sympatholysis of the upper extremity. Of the postganglionic sympathetic
supply to the upper extremity, 30% passes directly out of the thoracic outlet from the T2-T8 fibers to the brachial plexus and thus escapes the stellate ganglion (fused C7-T1 ganglia).
The efficacy of stellate ganglion block in conditions such as phantom limb pain, postherpetic neuralgia, and Me-niere disease have yielded questionable results.
Duration of Benefit
The duration of relief with diagnostic blocks is variable; however, there is evidence that repeated blocks may overall decrease the level of sympathetically mediated pain. Radiofrequency ablation of the stellate ganglion is generally avoided to prevent a permanent Horner syndrome.
This block can be performed either blind or by using fluo-roscopy. The advantages of fluoroscopy include visualization of the C7 transverse process (which if targeted carries a higher incidence of pneumothorax and intra-arterial injection) and visualization of the local anesthetic spread. Intravenous access is mandatory in this procedure, which may be associated with rare but potentially critical, emergent complications. The patient is placed supine with a small roll or pillow between the shoulder blades to improve extension of the neck. The patient is asked to open his or her mouth in order to relax the neck muscles. After palpation of the cricoid cartilage to determine the level of the C6 transverse process, the carotid pulse is felt and the sheath is then displaced laterally. A 22-gauge, short beveled 5-cm needle is then advanced between the ster-nocleidomastoid muscle and the trachea until bone is encountered (C6 tubercle); the needle is withdrawn 3 to 5 mm to avoid injecting the substance into the longus coli muscle. A test dose of 0.5 to 1.0 mL is injected to exclude intravascular injection, since as little as 0.5 mL of local anesthetic could result in seizure and loss of consciousness. This is followed by injection of 8 to 12 mL of local anesthetic (local anesthetic concentration can be reduced because autonomic C-fibers are small with no myelin).
Potential complications include the following:
Birklein F. Complex regional pain syndrome. J Neurol. 2005;252:131.
Marples IL, Atkin RE. Stellate ganglion block. Pain Rev. 2001;8:3-11.
Pather N et al. The anatomical rationale for an upper limb sympathetic blockade: preliminary report. Surg Radiol Anat. 2004;26:178.
Schurmann M et al. Assessment of peripheral sympathetic nervous system function for diagnosing early post-traumatic complex regional pain syndrome type 1. Pain. 1999;80:149.
The psoas major muscle and fascia separate the sympathetic chain and ganglia from the somatic nerves at the L2 to the L5 levels; the lumbar sympathetic chain contain both preganglionic and postganglionic fibers to the pelvis and the lower extremities. The sympathetic chain and ganglia are situated close to the anterolateral side of the vertebral bodies at the lumbar level; the best site for the needle tip placement would be the lower one-third of the L2 or the upper third of the L3 body. The rami communicantes course in a fibrous tunnel around the vertebral body; thus, caution is necessary when using a paramedian approach for neurolytic sympathectomy because the neurolytic agent could backtrack and cause ipsisegmental somatic painful neuritis.
Fluoroscopy is used for optimum needle placement. Accurate diffusion of the local anesthetic is based on the
optimal spread of the contrast material. After temperature probes are attached to the feet of the patient to monitor skin temperature, the skin on the patient's back is prepared and draped. The skin is then infiltrated with local anesthetic 7 to 10 cm lateral to the spinous process of L3. A22-gauge, 6- to 8-inch needle is directed toward the upper or middle third of the L3; the correct positioning of the needle anterior to the psoas fascia is verified using a loss-of-resistance technique. Correct placement of the needle is identified by injecting nonionic contrast showing a linear spread along the anterolateral aspect of the vertebral body. The contrast material is followed by injecting 15 to 20 mL of local anesthetic (may use bupi-vacaine 0.375%) while monitoring the increase in the lower extremity temperature.
When performing a neurolytic block, a solution of phenol 6% in Conray-420 dye (to add visibility while injecting the neurolytic agent) is used. The injection is performed while the C-arm is in the lateral position to detect any retrograde spread of the dye with resultant somatic neuritis.
Possible complications associated with lumbar sympathetic block include the following:
The celiac plexus is located retroperitoneally in the upper abdomen at the level of T12-L1 vertebrae. This plexus innervates most of the abdominal viscera, including the stomach, liver, biliary system, pancreas, spleen, kidneys, adrenals, and small and large bowel through the splenic flexure. The celiac plexus receives pregan-glionic sympathetic contribution from the greater (T5-T10 spinal roots), lesser (T10-T11), and least splanchnic (T11-T12) nerves, which relay in the celiac ganglia after running in the posterior mediastinum and traversing the crura of the diaphragm; postganglionic fibers run along the course of blood vessels to innervate the abdominal viscera. The ganglia receive parasympathetic contribution from the vagus nerve. The celiac ganglia are formed by the right and left splanchnic nerves with a network of interconnecting fibers and a great anatomic variability.
Celiac plexus block has proved both efficient and safe for the treatment of inoperable pancreatic cancer, with patients experiencing sustained pain relief for up to 24 weeks following neurolytic blocks; patients also required fewer medications with resultant decreased side effects related to the medications. This effect extended to other intra-abdominal malignancies of the upper abdomen. Some of the factors that may affect the efficacy of the block include the anatomic site of the tumor, with cancer head of pancreas showing more favorable responses compared with cancer body or tail. As a rule of thumb, celiac plexus block should be implemented early to maximize the benefits to the patient and to avoid technical difficulties related to the late spread of the tumor. The efficacy of celiac plexus block for chronic pancreatitis pain has been less established with studies yielding different results. Patients over 45 years of age and those who had never undergone pancreatic surgery were more likely to experience pain relief.
Multiple techniques have been described for the celiac plexus block, including the classic retrocrural approach, the transaortic approach, and the anterior approach.
Following are potential complications of celiac plexus block injections:
Cunha JE et al. Surgical and interventional treatment of chronic pancreatitis. Pancreatology. 2004;4:540.
Gress F et al. Endoscopic ultrasound-guided celiac plexus block for managing abdominal pain associated with chronic pancreatitis: a prospective single center experience. Am J Gastroenterol. 2001;96:409.
The superior hypogastric plexus mediates most of the nociceptive afferents from the pelvic organs. It receives preganglionic sympathetic fibers from the aortic plexus and the L2, L3 sympathetic nerves; it also receives preganglionic parasympathetic fibers from S2 and S3. The superior hypogastric plexus is continuous with the in-termesenteric plexus and is located retroperitoneally, inferior to the origin of the inferior mesenteric artery. It lies anterior to the lower part of the abdominal aorta, its bifurcation, and the middle sacral vessels; it is located anterior to the L5-S1 vertebrae.
Despite the paucity of data on the long-term efficacy of the superior hypogastric block, its use as a diagnostic block for chronic nonmalignant pelvic pain syndrome is well established. Conceptually patterned after celiac plexus block, hypogastric plexus block can be used to delineate the source of pain in such conditions as endometriosis, adhesions, interstitial cystitis, and irritable bowel disease. In malignant pelvic pain, sympathetic blocks should be intended as adjuvant techniques to reduce analgesic consumption and not as a panacea, given that multiple pain mechanisms are often involved because progression of disease is able to change the underlying pain mechanisms. Patients who respond favorably to diagnostic blocks have a higher success rate with neurolytic blocks.
Due to the proximity of the iliac vessels, intravascular injection and vascular injury are possible complications. Other potential complications include epidural, subarachnoid, and intraperitoneal injection as well as discitis with the transdiscal approach.
de Oliveira R et al. The effects of early or late neurolytic sympathetic plexus block on the management of abdominal or pelvic cancer pain. Pain.2004;110:400.
Erdine S et al. Transdiscal approach for hypogastric plexus block. Reg Anesth Pain Med. 2003;28:304.
Mercadante S et al. Pain mechanisms involved and outcome in advanced cancer patients with possible indications for celiac plexus block and superior hypogastric plexus block. Tumori. 2002;88:243.
Ganglion impar is a single retroperitoneal structure that represents the most caudad ganglia of the sympathetic chain. It is also known as the ganglion of Walther. The location of the ganglion is typically midline, anterior to the sacrococcygeal junction, where it represents the confluence of the two sympathetic chains on each side to form a single structure in the midline. However, the exact location of the ganglion is variable.
Most of the long-term efficacy data are reported with malignant perineal pain, with reported efficacy of complete relief in 50% of the patients and 60 to 90% pain relief in the remaining 50% of patients in one series. Cryoablation and neurolysis as a means for long-term relief of cancer-related pain should be considered in the armamentarium of pain procedures as a useful adjunct to oral pharmacologic therapy.
With the patient in a prone position, the area is prepared and draped. After making a skin weal, a 20-gauge 1.5-inch needle is inserted through the sacrococcygeal ligament and advanced until the tip is just posterior to the rectum. For diagnostic purposes, 5 to 8 mL of local anesthetic (1% lidocaine or 0.375% bupivacaine) is injected. For neurolysis, 4 to 8 mL of 10% phenol is used.
This is a relatively safe block; however, potential complications include rectal perforation, infection, and bleeding.
Han KR et al. Effects of neurolysis of the ganglion impar on the hyperhidrosis in the buttock and perineum. J Korean Pain Res Soc. 2001;11:114.
Oh CS et al. Clinical implications of topographic anatomy on the ganglion impar. Anesthesiology. 2004;101:249.
Epidural Corticosteroid Injection
Epidural corticosteroid injection is intended to deliver the medications in the vicinity of the inflamed nerve root; the therapeutic effects of epidural corticosteroids are attributed to an inhibition of synthesis or release of proinflammatory substances. Corticosteroids block phospholipase A2, which inhibits the conversion of phos-pholipids to arachidonic acid. NSAIDs work by a different mechanism, inhibiting the cyclooxygenase pathway. Failure of NSAIDs to produce pain relief, therefore, does not preclude the use of corticosteroids. Local infiltration of betamethasone at a nerve root compression model showed significant decrease in the expression of substance P, which proposes a possible direct effect of corticosteroids on pain mediators as well. Epidural installation of corticosteroids is not hampered by the decrease in local blood flow, which is frequently seen with com-pressive lesions. This can explain the decreased efficacy of orally administered corticosteroids, since the effectiveness is presumed proportional to the local concentration of the corticosteroids.
Despite the widespread use and acceptance of epidu-ral corticosteroid injection, it remains controversial, especially outside the United States. The question about whether there are long-term benefits for patients remains unanswered.
When epidural corticosteroid injections were given on an outpatient basis to persons with low back pain and sciatica, repeated injections improved the success rate and provided a safe, cost-effective means of treatment without the necessity of hospital admission. Most patients received a series of three epidural corticosteroid injections with progressive improvement after the second and third injection, which is a common pattern of practice in many pain management centers. The reported success rates varied greatly ranging anywhere from 18 to 90%. Selective nerve root injections of corticosteroids were significantly more effective than those of bupivacaine alone. Caudal epidural corticosteroid injections using triamci-nolone was superior to placebo, with reported better pain control and mobility at 4 weeks.
The choice of the patient and the technique used is pivotal when epidural corticosteroid injection is considered. Patients who report superior pain relief include those with a higher educational background, a primary diagnosis of radiculopathy, and pain duration of less than 6 months. Those patients involved in litigations, who were unemployed, had constant back pain, and were symptomatic for 6 to 24 months historically had higher failure rates.
The choice of the technique should be symptom oriented. Patients with unilateral radicular symptoms are
good candidates for transforaminal epidural cortico-steroid injections, whereas the interlaminar or caudal approach is more appropriate for patients with axial back pain resulting from degenerative spinal stenosis or for patients with bilateral radicular symptoms.
The transforaminal approach is showing very encouraging results, with long-term success rates of 71 to 84%. The advantages of this approach include decreased risk of dural puncture and delivery of the medications in the anterior epidural space very close to the irritated nerve root. Transforaminal approach is particularly beneficial in large disk herniation, foraminal stenosis, and lateral disk herniations.
Different approaches to the epidural space have been described. Traditionally, two techniques have been used: the interlaminar and the caudal approaches. The trans-foraminal approach as mentioned above is a novel approach that has proved effective in the hands of experienced clinicians.
Regardless of the technique used, the use of fluoroscopy seems to play a crucial role as far as corticosteroid delivery and minimizing risks. Epidural corticosteroid injections have been demonstrated to be very safe, although inhibition of the hypothalamic-pituitary axis is possible. It is generally considered safe to repeat the injections. In a national survey, the average number of epidural cor-ticosteroid injections a single patient received was 5 to 7 per year; this survey included both academic as well as private practice pain centers.
Central neuraxial injections generally can result in the following:
Neurolytic Nerve Blocks
Visceral cancer pain can be very difficult to treat; neurolytic sympathetic blocks can be effective. In one study despite optimized systemic analgesic therapy (SAT), patients with unresectable pancreatic cancer treated with SAT only did not have as effective pain control as a comparable group that received neurolytic celiac plexus block.
Because of possible side effects that can adversely alter the quality of life, candidates for neurolysis should have limited life expectancy.
Solutions used for neurolytic block include phenol or ethyl alcohol. Phenol, in a concentration of 5 to 6%, has the advantage of being painless on injection, as well as the fact that it can be mixed with contrast material.
Ethyl alcohol is usually used in an undiluted form (95% and above). Alcohol injection may be painful secondary to irritation of the perineurium; therefore, some clinicians inject local anesthetic prior to the neurolytic block.
The most ominous complication related to alcohol neurolytic blocks includes alcohol-induced neuritis, which can occur during sympathetic blocks secondary to retrograde spread of the neurolytic agent injuring the somatic nerves. Therefore, neurolytic blocks should only be performed by an experienced interventional pain specialist. Pain related to alcoholic neuritis subsides within weeks to months in most cases.
Local Anesthetic Toxicity
Since local anesthetic is used in all the above-mentioned blocks, it is important to be aware of the possible complications related to local anesthetic overdose and toxicity, including neurotoxicity, cardiac toxicity, allergies, and methemoglobinemia.
Neurotoxicity can range from mild toxicity (including ringing in the ears, circumoral numbness, metallic taste, lightheadedness, and confusion) to severe toxicity (progressing from grand-mal seizures to coma and death).
Local anesthetics cause a dose-dependent inhibition of cardiac contractility and conduction, which may result in cardiovascular collapse and cardiac arrest. Guidelines of maximum dosage should be strictly followed, and in-travascular injection should be avoided.
Allergy to local anesthetics is very rare; however, allergy to aminoester local anesthetics has been reported. These drugs are derivatives of p-aminobenzoic acid, which is known to be allergenic.
A unique systemic side effect associated with a specific local anesthetic is the development of methemoglobine-mia after the administration of large doses of prilocaine. In most cases, this condition does not necessitate treatment and usually resolves spontaneously; however, intravenous administration of methylene blue can be used.
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Wong GY et al. Effect of neurolytic celiac plexus block on pain relief, quality of life, and survival in patients with unresectable pancreatic cancer: a randomized controlled trial. JAMA. 2004;291:1092.
Wong HK et al. Effects of corticosteroids on nerve root recovery after spinal nerve root compression. Clin Orthop Relat Res. 2002;(403):248.