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Because nerve block therapy is invasive, one must respect the risk/benefit ratio when considering the use of this technique in patients with neuropathic pain (also see Chapter 43 and Chapter 44 ). The evaluation scheme should render a diagnosis for which this form of treatment is reasonable. The more specific the diagnosis, the more focused can be the anatomic approach to nerve block therapy.[75] [76] Absolute contraindications to nerve block therapy include blood-borne infection, infection at the site of proposed needle insertion, major coagulopathy, and the refusal of the patient or his/her surrogate.[75] As the patient's physical and psychosocial circumstances change, the patient must be deemed appropriate for the planned treatment before every procedure. The mere ability to provide the therapy does not mean that it is indicated. One must be cautious with procedural sedation so as not to confound the veracity of the patient's feedback about the clinical results, which is subjective, after all.
In contemporary pain management, the practitioner must be capable of managing the immediate and the delayed side effects and complications from nerve block therapy. Follow-up visits relevant to the procedure provided are necessary to arrange for the next appropriate treatment. It is particularly important to document the percentage of change in the intensity of the pain and its duration, in the patient's functional ability, and in medication use when improvement has occurred. Over time, the benefit of nerve block therapy has been critiqued and its foundation in evidence-based medicine reviewed.[77] Donner and co-workers surveyed the use of nerve block therapy for evidence of its long-term effects.[78] They concluded that blocks have a diagnostic and prognostic potential but clinical evidence of its benefits is lacking,[75] and that the interpretation of the results is crucial in directing therapy. They emphasized the use of selection criteria in choosing patients for nerve blocks and the importance of the timing of such intervention.
Straus, in economic review of the cost of interventional therapy, examined the important factor of cost versus benefit that must be considered in therapeutic planning.[79] He reported the cost of medical treatment is thought to be between $9,000 and $19,000 per patient per year. Cost minimization analysis suggests that epidural steroid injection under fluoroscopy may not be justified, whereas spinal cord stimulation and intrathecal pump placement for drug administration may be justified when these concepts are applied.
The principle guiding the use of nerve blocks in managing pain can best be shown in reference to a most common problem seen by pain medicine specialists—low back pain. This is second only to headaches as a cause of chronic pain.[80] [81] The differential diagnosis is vast, the expenses for patient evaluation and treatment exceedingly high, and the problem very prevalent. The evaluation may reveal musculoskeletal pain with prominent myofascial trigger points. Myofascial pain is a common problem with a primary cause of pain injury to muscles, bones, and joints. The myofascial pain may also be a secondary consequence of pain from a distant site that results in postural alterations with clinically significant stress/strain of muscles or supporting tissues over time.[82]
It is common to inject trigger points, identified as rope-like tight bands or focal areas of maximal tenderness to palpations in muscles, with local anesthetics.[82] In recent years, the use of botulinum toxin has been broadened to include trigger point injections.[83] DiFazio and Jabbari have detailed the use of botulinum toxin in low back pain.[84] One should not underestimate the impact of such a simple intervention. The effectiveness of this treatment proves to the patient with ongoing pain and a previous poor response to treatment that something can indeed be done about the pain. These results dramatically change the patient's attitude to a more positive demeanor, enhancing his or her compliance with other rehabilitative treatments.
Myofascial pain should be distinguished from fibromyalgia, a chronic musculoskeletal syndrome characterized by widespread pain and hyperalgesia.[85] [86] As noted by Okifuji and Turk, although the prevalence of the syndrome is only 2%, the impairment of the patient's quality of life is high as are the health care costs.[85] Fibromyalgia is characterized by fatigue, severe muscle and joint tenderness, sleep disturbance, widespread body pain, morning stiffness, paresthesias, anxiety and/or depression, and headaches. The treatment of this syndrome requires much more than mere trigger point injections! A coordinated program of NSAIDs, therapy for reflex muscle spasm (with medication or self-regulation techniques), antidepressants to increase non-REM stage IV sleep, supportive psychological therapy, and physical therapy is often beneficial.
Complaints of low back pain may be explained on the basis of radicular pain.[80] [81] Often this pain starts with a traumatic event, such as lifting a heavy object while in an awkward position. The pain can be sharp and radiates from the low back into one or both of the lower extremities, and below the knee. It may be associated with sensory, motor, and/or reflex changes and is accentuated with coughing, straining, or other activity. This must be differentiated from neurogenic claudication, facet disease, or internal disk disruption. Rather, the pathology is related to a toxic spill of inflammatory mediators from the nucleus pulposus. NSAIDs do not profoundly block the subsequent inflammation. As discussed previously, these substances sensitize neural responses such that mild mechanical irritation of the inflamed nerve root results in severe pain. There has been a long history of empiric use of epidural injections of depo-steroids in patients with complaints of back pain.[80] [81] As reviews of such therapy are published, there has been a necessary refinement of criteria for selection of patients to receive epidural steroid injections (ESIs). In their contemporary primer on low back pain, Deyo and Weinstein[87] suggested that the workup of a patient with low back pain must answer three basic questions: Is there systemic disease causing the low back pain? Are there social or psychological stresses amplifying or prolonging the pain? Is there nerve root compression indicating that surgical evaluation is necessary?
Beyond that, it is evident that ESIs are not a generic treatment for all causes of low back pain. Rather, patients with clear signs of radiculopathy are more likely to respond favorably, since the precise level of pathology in the spine can be identified and depo-steroids can be placed accordingly. The intent of ESI therapy is to provide a high dose of steroid at the level of pathology to reduce the swelling of the nerve root, block c-fibers, stabilize nerve membranes, and decrease ectopic discharges from the inflamed tissue.[88] The subsequent decrease in pain encourages participation in rehabilitative physical therapy, which by allowing the patient to stretch and strengthen the muscles of the back, decreases the incidence of abnormal postural stress being put on the injured disk and thereby stops the leak of offending mediators. Because the disks leak into the epidural space, and not the subarachnoid space, the placement of deposteroids into the latter area is not therapeutic.
Fanciullo and associates surveyed 23 spine care center practices for patients referred with spinal or radicular pain to assess how published guidelines regarding ESIs were followed.[89] Of 25,479 patients, only 7.9% had ESIs recommended. This group had radicular pain with dermatomal distribution and positive neurological findings on examination; they also had a greater incidence of pain of more than 1 year's duration, a higher incidence of previous back surgery, and more co-morbidities such as congestive heart failure, hypertension, peripheral vascular disease, and diabetes than the non-referred patients did. These factors are not necessarily associated with high success of ESIs in resolution of the patient's clinical symptoms. It is important to note that the systemic effects of the depo-steroids are not benign (i.e., fluid retention, with additional risks in patients with renal insufficiency or congestive heart failure; increased blood sugar, important in diabetics; and metabolic effects).[88] In a review of ESI practice in the United States, Cluff and colleagues state that "the ideal dose and type of steroids have yet to be determined."[90]
There has been a long-held concern about tissue toxicity from the PEG content of the depo-steroid if it crosses into the CSF. Abram recommended that a test dose be given prior to the injection of depo-steroids, especially in patients with previous back surgery in whom the epidural space may be difficult to locate.[88] Some common side effects from this procedure include the ordinary risks of bleeding and infection associated with needle-based treatment, localized tenderness from needle placement, post-dural puncture headache, paresthesias, and anxiety-related symptoms such as lightheadedness and nausea.[90] Apparently the risks to patients concurrently taking NSAIDs are minimal. Horlocker and co-workers surveyed 1035 patients who had received 1214 ESIs; 32% of these patients had taken NSAIDs within 1 week of the ESI.[91] No spinal hematomas occurred and only 5.2% of the patients had evidence of blood in the catheter or needle.
The complications of interventional therapy are not to be lightly dismissed. In an elegant review, Fitzgibbon and associates published their comparison of 284 cases from pain medicine practices with 5125 claims related to surgery/obstetrical care in the American Society of Anesthesiologists Closed Claim Project.[92] It is evident that claims associated with the treatment of chronic pain are increasing and are mostly related to invasive therapies; ESI complications account for 40% of all chronic pain management claims. It is not known whether the change from the translaminar (midline) to the transforaminal (selective nerve root block) approach or the use of fluoroscopy to confirm correct needle placement and the spread of injectate have increased or decreased the potential complication rate.[77] [88] [93] [94] [95] [96] Botwin and co-workers reported a minor complication rate of 9.6% per injection in a retrospective cohort of 207 patients receiving 322 transforaminal lumbar ESIs.[97] Non-positional headache and increased back pain were the most common problems. In his economics-focused review, Straus emphasized the fact that the higher success rate of accurate placement, with fluoroscopy, by itself, is not evidence of benefit.[79] His cost analysis challenged the use of fluoroscopy, and he urged practitioners to strive for improved patient outcome, decreased complication rates, and documented reductions in health care costs as viable outcome targets.
The overall success rate of ESI varies from 18% to 90%,[88] [89] [90] [94] [98] [99] but there are marked variations in the numerous studies published concerning the patient population examined, the drugs used for injections, and the quality and duration of follow-up. The general consensus is that patients with radicular pain into the distal extremity with a duration of less than 6 to 12 months are prime candidates for a trial of ESIs. [75] [76] [80] [81] [88] [89] [90] [94] [98] [99]
As mentioned, the jury is still out on the decision whether the traditional translaminar approach is less
The use of intradiscal electrothermal (IDET) annuloplasty has been proposed for patients with more than 6 months of discogenic (axial, but not radicular or facet) pain, at best a moderate response to conservative therapy, and with symptoms increased by flexion or sitting.[100] [101] IDET annuloplasty is a minimally invasive procedure that destroys nociceptive fibers in the disk annulus with a controlled heat lesioning technique. Theoretically, this causes contraction of the collagen and stabilizes the disk. Saal and Saal reported that IDET annuloplasty in 58 patients, as chosen by the criteria stated previously, resulted in a significant decrease in VAS and body SF-36 scores, and increases in sitting and physical function as well as quality of life SF-36 scores.[101]
If the disk is not a major source of low back pain complaints, it is common for the patient to demonstrate facet-related pain upon evaluation.[80] The patient may complain of pain that is referred to the buttocks or thighs, but not commonly below the knee. The pain increases with extension and rotation of the spine, may be associated with reflex muscle spasm that decreases lumbosacral spine range of motion in the absence of radicular findings, and can be related to signs of degenerative changes of the facet joints on radiography. Approaches to the management of this pain include injecting the facet joint space or blocking the medial branch of the posterior primary ramus nerve to the joint.[102]
If diagnostic nerve blocks with local anesthetics prove beneficial in reducing the patient's symptoms, a radiofrequency lesion of the medial branch nerve is commonly performed. This is a heat-based, focal therapy, the randomized controlled trials for which were reviewed by Geurtz and associates.[103] They concluded that there was "moderate evidence that radiofrequency facet denervation is better than placebo."[103] In part, these middle-of-the-road results may be related to the multitude of structures in the low back that can cause similar pain (i.e., the sacroiliac joints) and the wide array of diagnoses for which medial branch blocks are attempted. This form of treatment may gain application in patients with other than facet sites of pain, such as patients with discogenic pain, CRPS, and sacroiliac joint dysfunction.[102]
In some patients with intractable low back pain that radiates into at least one extremity, spinal cord stimulation (SCS) therapy may be considered. This was first used in the late 1960s for patients with failed back surgery syndrome (FBSS).[104] This therapy involves the placement of stimulating electrodes in the epidural space, surrounding the entry level of noxious input into the spinal cord. The system, consisting of a pulse generator or radiofrequency receiver, and wires connected to the electrodes, is implanted in carefully selected patients who have passed a percutaneous trial of the SCS therapy (resulting in at least a 50% decrease in pain, a decrease in medication use, and a definite increase in function) and who have been cleared by psychology screening. The application of this modality has been broadened to include some patients with CRPS, peripheral ischemic disease, and peripheral neuropathy, because there are no addictive potential or systemic side effects.[104] [105] [106] [107] Improved outcomes are anticipated as patient selection criteria are refined, more experience is gained with the technique by more practitioners, and more advances in the technical components of the systems are promulgated.[108] Although there is a notable initial outlay cost for SCS therapy, the treatment can compete with traditional treatment in our fiscally conscious medical reimbursement environment.[79] [109]
The final inclusion in advanced pain therapies for neuropathic pain is the implantation of an intrathecal drug delivery system.[110] The use of short-term intrathecal drug therapy is a common practice in acute pain management, and an implanted system is not uncommon in cancer pain management. Drugs such as opioids, local anesthetics, clonidine, and baclofen have been used in patients with neuropathic pain. The lack of standardized outcomes for such therapy has resulted in some patients being treated as a random choice or out of desperation because of the failure of more conservative and even some extreme measures.
As with nerve blocks and SCS therapy, intrathecal drug management is an invasive therapy for which patients must be carefully selected. Generally, the patient should have an identified pathology for which no further surgery is indicated and for which conservative therapy has failed. Psychological screening is of great benefit in revealing patients with subtle substance abuse issues, irresponsible healthcare behaviors, rigid attitudes about ever being functional again, and unrealistic expectations of the therapy. As the potential for the delivery of analgesic treatment by this route is so vast, research must continue so drugs with potent clinical effects, a lack of side effects, and no neurotoxicity will become more available.[111]
A major realm of pain medicine practice for which nerve block therapy is common includes patients with clinically significant involvement of the sympathetic nervous system (SNS).[75] [76] [77] [78] A common diagnosis is complex regional pain syndrome (CRPS), also called reflex sympathetic dystrophy. This entity involves the somatic, sympathetic, and somato-motor nervous systems, but the exact explanation of the interaction of these symptoms has not been defined. CRPS can follow minor trauma that does not result in demonstrable tissue damage (such as strains, sprains, infections) (type I), or injury to major nerves (type II), viscera, or the CNS.[112] The intensity of the symptoms do not correlate with the severity of the
Clinical signs and symptoms include burning pain, allodynia or hyperalgesia, edema, changes in blood flow (vasomotor) and sweating (sudomotor) in the affected limb(s) and muscle-joint changes, tremors, weakness, and dystonia.[115] Criteria for the diagnosis of CRPS have been published, but no system has achieved the desired uniformity of application or the necessary sensitivity and specificity. [116] Also, because specific diagnostic tests are lacking, the diagnosis is made by extracting findings from the history and physical examination.[115]
Treating the cause of the CRPS does not constitute its management. A common treatment for CPRS has been to interrupt the alleged somatic-sympathetic interaction by performing nerve blocks of the SNS (also see Chapter 44 ), although the rationale for this is challenged by consideration of the contemporary mechanisms of sympathetically mediated pain.[75] [76] [117] The therapeutic or diagnostic effect of the specific technique of sympathetic blockade should not be confounded with sensory or motor block. Cervicothoracic (i.e., stellate) ganglion block is performed with up to 10 mL of local anesthetic at the C6 level with an anterior paratracheal insertion site.[75] [76] The admitted unreliability of assessing the adequacy of the subsequent block clinically challenges the conventional wisdom that only a positive response is necessary for this block to be considered diagnostic of CRPS.[117] [118] Lumbar sympathetic blocks are performed at the L2, L3, and L4 levels or with a single needle at L2 or L3.[75] [76] [119] A 22-gauge needle is advanced, usually under fluoroscopic guidance, to the anterolateral border of the chosen vertebral body level (a test injection of x-ray dye will confirm proper needle placement), and 10 to 15 mL of local anesthetic are injected.
In both of these types of sympathetic blockade, the regional anatomy involved in the technique predicts the potential side effects and complications from errant needle placement or drug administration. These possibilities are very important if neurolytic agents (e.g., 6% to 10% aqueous phenol or 50% to 100% absolute alcohol) are used for lumbar sympathetic block. Genitofemoral neuralgia has been a reported complication in 8% to 10% of patients after neurolytic blockade of the lumbar sympathetic chain.[119] [120]
As with the exact utility of SNS blocks in CRPS, the use of chemical sympathectomy for neuropathic pain has been challenged.[117] [118] [120] Based upon a Cochrane database review, chemical sympathectomy was shown to have only a temporary effect, and that on the cutaneous allodynia component of the patient's clinical presentation.[117]
With serial local anesthetic blocks, a staircase pattern of improvement is sought, meaning that pain is reduced more and for a longer period of time with each block. Progress with the all-important rehabilitative physical therapy is enhanced when pain is reduced and joint range of motion restored. Improved functional recovery is the ultimate goal of treatment. If benefits are not progressive but definitive with each block (i.e., temporary effects are obtained with serial blocks), consideration may be given to radiofrequency ablation or thoracoscopic/surgical sympathectomy. [76] [115]
The most contemporary treatment offered for patients with enduring CRPS is spinal cord stimulation (see earlier). This popular treatment has not yet passed rigorous scrutiny as to its utility in such patients, even though it is touted to inhibit A-β fiber-mediated hyperexcitability of dorsal horn neurons, reduce SNS outflow, and increase peripheral blood flow.[121] Van Hilten and associates reported that the administration of intrathecal baclofen to patients with CRPS-related dystonia showed benefit in the upper extremity but not the lower extremity.[122] Rauck and co-workers have shown that epidural clonidine infusion may be beneficial in selected patients. [123] Suresh and colleagues reexamined the use of intravenous regional techniques, their application using lidocaine and ketorolac proving to be at least moderately effective in children and adolescents.[124]
Blockade of the celiac plexus, another technique involving the SNS, is notable for its continued use in patients with intractable pain due to cancer of the pancreas or other upper abdominal viscera.[76] [80] [125] [126] Successful block of the celiac plexus denervates the abdominal organs from the gastroesophageal junction to the splenic flexure of the large intestine. The exact utility of this technique in patients with chronic, non-cancer pain has yet to be determined. Its consideration in such patients merits a serious review of the risks and benefits, especially when the use of neurolytic agents is contemplated.
Further along the sympathetic chain, the technique of blocking the superior hypogastric plexus has evolved.[127] This bilateral, retroperitoneal plexus is located at the L5-S1 level (the sacral promontory) close to the bifurcation of the common iliac vessels. It innervates the pelvic viscera and its blockade has application in patients with cancer and non-cancer pain. The union of the bilateral sympathetic chains into a single, retroperitoneal plexus is called the ganglion impar, or the ganglion of Walther. It is located anterior to the coccyx at the sacrococcygeal junction.[127] This blockade denervates the lower pelvic organs and the perineum.
It should be emphasized that patients suitable for neurolytic blocks must be carefully selected and that the technique must be impeccable, so as not to obviate the advantages of nerve block therapy (generally, outpatient procedures with less risk of surgery, being repeatable, being increasingly available, and with a positive effect allowing a reduction of other treatments).[75] [76] [77] Factors that influence the decision to use neurolytic regional analgesia techniques include the patient's general medical condition (i.e., coagulation and immune status); the location and rapidity of progression of the pain generator; the type of pain; the patient's goals for treatment; his/her life expectancy; the inherent risks of the specific procedure; the
Theoretically, patients who are best suited for neurolytic blocks have a localized source of pain (the pain from which is decreased with a diagnostic block); absence of coagulopathy, blood-borne infection and infection at the proposed needle insertion site; satisfaction with the informed consent that details the risks and benefits of the procedure; and an attitude that will allow them to tolerate the potential sensory/motor/continence impairment/neuropathic pain.[128]
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