Pain is the most common reason for patients to seek medical attention. Chronic pain has major effects on patients physically, psychologically, and socially and is a major cause of healthcare costs, disability, and lost workdays. There are numerous therapies for the treatment of chronic pain. Although there are a few medications with FDA indications for the treatment of pain, the majority of treatments are off-label use of drugs that have modest effects on pain. Interventional therapies have been used for decades to treat chronic pain; however, there is limited evidence that they result in long-term reductions in pain. Why are these therapies continuing to be used if there is no solid evidence supporting efficacy?
Most studies done on the interventional therapies base outcome on cure rather than palliation. Ninety percent of the practice of medicine is based on palliation, as there are cures for less than 10 percent of all disease states. The interventional therapies should be viewed as palliative rather than curative, and some patients will require repeated interventional therapies for prolonged periods of time for pain relief and improved quality of life. This article will discuss the various interventional therapies used to treat chronic pain, provide the current evidence on efficacy, and provide recommendations on how these therapies can be used to the maximum benefit of the chronic pain patient.
Evidence-based Medicine and Interventional Pain Therapies
Evidence-based medicine is important to improve outcomes with all medical therapies. However, strict adherence to evidence-based medicine can also be detrimental to patient care if the treatment does not lend itself to rigorous clinical trials or if the outcomes of the research are based on a small, highly selected patient population that may not be representative of the actual population. This can result in patients being denied very effective treatments. Evidence-based medicine is intended to measure four outcomes: efficacy, safety/tolerability, ease of use, and costs. The highest level of efficacy measurement is through multicenter, double-blind, randomized, placebo-controlled trials. All of the current pharmaceuticals that have FDA approval for the treatment of pain have passed this standard. However, most of the off-label pharmaceuticals and all of the interventional therapies have not been subjected to this level of efficacy measurement.
There are obvious reasons why interventional therapies have not been evaluated with multicenter, blinded, randomized trials. These include ethical limitations and difficulties in blinding invasive therapies, cost prohibition, and difficulties in recruiting subjects for such studies. Therefore, in the absence of high-quality, efficacious trials, one relies on clinical experience to determine efficacy. Many of the interventional therapies for pain fall into this category, with small clinical trials and vast clinical experience demonstrating efficacy. Clinical experience also demonstrates safety for most, but not all, interventional therapies with reasonable ease of use and costs as compared to chronic pharmaceutical use.
Epidural Steroid Injections (ESI)
Epidural steroid injections (ESI) are one of the most commonly used interventions to manage both acute and chronic spinal radicular pain. Of all the interventional therapies for pain management, ESIs have been the most studied. A recent report from the therapeutics and technology subcommittee of the American Academy of Neurology concluded that ESIs for the treatment of lumbosacral radiculopathy did not result in pain relief beyond three months and did not impact function or the need for surgery. Since 1971, there have been 18 studies involving a total of 1,081 subjects using the interlaminar and caudal approach to the epidural space. Twelve of the 18 studies showed significant pain relief up to three months. Eight of the studies showed pain relief beyond three months. Seven of the studies were double blind, placebo controlled, and, of these, five showed significant relief of pain up to three months. So why did the American Academy of Neurology conclude that the routine use of ESIs was not indicated for the treatment of radiculopathy? Because they were evaluating the outcomes based on cure rather than palliation.
A major problem with the studies on the interlaminar and caudal approach to the epidural space is that fluoroscopy was not used thus the exact level of steroid placement was unknown. Since the advent of fluoroscopic guidance for ESIs, the use of the transforminal approach has become a more common practice, which allows precise placement of the steroid at the level of radicular symptoms. Since 1996, there have been three published double-blind, randomized, controlled trials evaluating this technique in a total of 264 subjects. All three trials demonstrated both short- and long-term reduction in pain.
With the exception of cervical transforaminal approach, the risk associated with ESIs is very low. There have been many reports of serious neurological injury, including spinal cord and brainstem infarcts, with some leading to death after cervical transforaminal steroid injections. The mechanism of this complication appears to be related to the injection of particulate steroid into the vertebral or spinal radicular artery leading to massive central nervous system infarction. However, there is some evidence that the carrier of depomedrol may be toxic to the blood brain barrier. The use of dexamethasone, a non-particulate steroid, appears to be void of this risk.
Given the low risk of ESIs, it is reasonable to offer patients who want to avoid surgery repeated injections no more often than every three months if they demonstrate prolonged pain relief. However, patients with severe radicular pain unresponsive to ESIs will likely benefit from early surgical intervention. The SPORT study shows that early recovery in such patients is quite good; however, at one year there was no difference in outcome between those that received early surgery and those that were managed conservatively.
Treatment of Facet Joint and Sacroiliac Joint Pain
Facet pain has been estimated to account for as high as 47 percent of low back pain and 63 percent of cervical pain. Blockade of the medial branches to the facet joints can be diagnostic for pain arising from these structures. Many patients who respond to medial branch blocks will benefit from radiofrequency lesioning. A randomized sham study of radiofrequency lesioning for cervical facet pain in 24 patients resulted in an average duration of pain relief of 263 days in the treatment group as compared to 80 days in the sham group. A randomized sham study of this technique for low back pain was performed in 31 patients. At 12 months, seven patients in the treatment group continued to report pain relief as compared to two patients in the sham group.
Sacroiliac joint pain is a common cause of chronic low back pain with an estimated incidence of up to 30 percent. The injection of corticosteroid into the joint can result in significant relief; however, there are no clinical studies evaluating the long-term benefit.
Spinal Cord Stimulation (SCS)
Spinal cord stimulation (SCS) involves placing electrodes in the posterior epidural space over the dorsal columns of the spinal cord. Stimulation of the dorsal columns produces pleasant parasthesias over large areas of the body corresponding with the level of the dorsal column stimulated. Spinal cord stimulation is usually reserved for extremity pain but newer technologies are allowing stimulation of pain located in the trunk such as the low back and thoracic region.
The most common indication of SCS is for patients who have failed back surgery. Re-operation on these patients has been shown to have poor outcomes, and SCS is a reasonable alternative. Studies have demonstrated a 50–70 percent success rate (defined as >50 percent reduction in pain) with a three-to-seven year follow-up. Most failures after two years of therapy are usually due to fibrosis around the contact, which inhibits the flow of the electrical current. Newer technology allows for the current to be fractionated resulting in the ability to steer the current through the impendence created by the fibrosis. This will likely result in better long term outcomes.
Spinal Drug Delivery
The spinal cord dorsal horn is rich in receptors and ion channels that are involved in pain transmission. By delivering drugs directly into the spinal fluid that target these mechanisms, pain can be reduced using a fraction of the dose required for systemic delivery with fewer side effects. For terminally ill patients, this can be achieved with a percutanous catheter and external pump. For the long-term delivery of intraspinal medications, an implanted pump is required that is refilled percutaneously every 30–90 days.
Most studies evaluating the efficacy of spinal drug delivery report on retrospective chart reviews that show good to excellent pain relief in 60–90 percent of subjects. A recent randomized controlled trial of implanted spinal drug delivery compared to medical management in over 200 cancer pain patients showed that significantly more patients who received the spinal infusion reported successes and fewer drug side effects.
Ziconotide, a non-opioid, is the first FDA approved drug for intrathecal use in almost two decades. It was subjected to rigorous multicenter, randomized, controlled trials in over 1,200 subjects and showed a significant decrease in pain over placebo.
Although there are high up-front costs of implanted spinal drug therapy, cost analysis shows that at 22–25 months there are cost savings associated with this therapy.
Conclusion
Pain is often multi-factorial with both physical and psychological components driving the pain. As a single modality, interventional therapies are less effective than when integrated into a multidisciplinary model of pain management. Some patients will do well with interventional therapies alone; however, many patients will require that this therapy be used with other treatments, such as pharmacologic, psychologic, and rehabilitative approaches. There is evidence that the interventional therapies result in prolonged pain relief. However, like almost all other therapies for pain, they should be viewed as palliative, not curative. For some, it is a lifelong treatment. For others it is a short-term treatment that may buy the patient time until they receive treatments directed at long-term pain relief.
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