Chronic pain is defined as any pain lasting for more than three to six months. Millions of people suffer from chronic pain every year, with tremendous costs to our country for health care, rehabilitation, lost work productivity, and the emotional and financial burden it places on patients and their families. The goal of any treatment protocol in management of chronic pain is to decrease pain and improve functional status. Care is often long-term, with frequent reassessment and therapy adjustment. Management involves a multidisciplinary integrated approach including medication, physical therapy, behavioral therapy, and vocational evaluation and training. Since medication use can be limited by side effects,interventional techniques are a necessary part of any multidisciplinary approach. Interventional techniques include trigger point injections and implantable devices, such as spinal cord stimulators or intrathecal drug delivery systems. Singly or in combination with other options, they can be quite effective in pain control and increase
the chances of returning patients to active life.
Interventional Techniques
Pain signals are transmitted from a peripheral site, or site of injury, to the cortex in a complex manner involving several orders of neuronal connectivity and several pain modulating pathways. Trigger point injections, nerve blocks, sympathetic blocks, epidural steroid injections, spinal cord stimulators, and intrathecal therapies target different steps of the pain pathways. Trigger point injections: A myofascial trigger point is “a cluster of electrically active loci, each of which is associated with a contraction knot and a dysfunctional motor endplate in skeletal muscle” (Simons, Travell, and Simons 1999). Trigger points usually affect postural and masticatory muscles and present as poorly-localized muscular pain or headache. They can be active or latent. Latent trigger points affect almost half of the population by adulthood. These are activated by sudden overloading contraction, viral infection, cold, fatigue, or increased emotional stress. Local anesthetic injection into these trigger points has been shown to decrease pain in clinical conditions like chronic headaches, myofascial pain syndrome, and fibromyalgia (Hong and Hsueh 1996). The possible complications from these injections are local site infection, hematoma formation or sometimes increase in pain.
Somatic nerve blocks:
Somatic nerve blocks are used in managing pain for both acute and chronic painful conditions. The somatic nerve to be blocked depends on the site involved and the type of chronic pain syndrome. Specific complications related to these blocks are permanent peripheral nerve damage and inadvertent intravascular injection of the local anesthetics.
Sympathetic nerve blocks:
Sympathetic nervous system hyperactivity can cause painful syndrome (CRPS). Some pain fibers also traverse the sympathetic tract to the spinal cord.
Epidural steroid injections:
Epidural steroid injections have modest benefit in neck, low back pain, and radicular pain (Benoist, Boulu, and Hayem 2011). Epidural steroids decrease nerve root inflammation and irritation caused by herniated disc or inflamed synovial facet joint. Most studies suggest modest benefits for variable periods of two weeks to perhaps three months. The short-term benefit from epidural steroid injections and the natural history of radicular pain may complement each other in regard to patient clinical improvement.
Radio-frequency ablation (RFA) or neurolytic nerve blocks:
Neurolytic blockade and RFA are valuable tools designed to produce prolonged interruption of neural transmission. The common rationale for neurolytic block,
prolonged relief of intractable pain, is used most often in patients with malignancy. Its role in non-malignant conditions is not clear and is individualized on case-to-case basis. RFA uses high frequency current (pulsed or ablative) to modulate the neural transmission. Clinically, it is most commonly used for cervical or lumbar facet pain (Dreyfuss et al. 2000) and trigeminal neuralgia (Taha and Tew Jr. 1996) but can also be used for sympathetic block, occipital neuralgia, and other chronic painful conditions.
Spinal cord stimulators (SCS) and peripheral nerve stimulators:
Spinal cord stimulators are effective in radicular and neuropathic pain,
e.g., CRPS in extremities. SCS and physical therapy used together improve quality of life and reduce pain in 50% of properly selected patients (North et al. 2005). Similarly, peripheral nerve stimulators are effective in patients with neuralgias, e.g., greater occipital or ilio-inguina / iliohypogastric neuralgia (Mobbs, Nair and Blum 2007; Schwedt et al. 2007). Complications specifically related to permanent implants include the risk for infection, epidural hematoma, lead migration and dural puncture.
Epidural and intrathecal drug delivery systems:
Delivering medications directly adjacent or into the spinal canal decreases the amount needed to produce analgesia and decreases the systemic side effects of high doses of narcotics. There are several newer medications, e.g., zicotinide (Prialt, an NSAID), that are effective for epidural and intrathecal use in conditions resistant to all other pain medications. Possible complications with intrathecal drug delivery system include local infection, meningitis, CSF seroma, catheter granuloma, catheter migration, respiratory depression, post-dural puncture headache, and epidural hematoma.
Summary
Pain procedures are quite safe; large numbers are performed in everyday clinical practice. Catastrophic events such as permanent nerve damage, epidural hematoma, epidural abscess, and paraplegia, occur only infrequently. However, even in the era of evidence-based practice, it is difficult to develop consistent criteria for pain intervention effectiveness, as evidence for many commonly-performed procedures is not available in the literature. In practice, pain reduction does not necessarily translate into improved function, although we often observe a broad spectrum of response to an intervention. It is imperative to consider risk and benefit of each intervention for each patient, individualizing the plan of care based on the individual’s comorbidity, motivation, and psychology.
The authors are past or present members of the UPMC St. Margaret Pain Medicine Center, University of Pittsburgh, 200 Delafield Road Suite 2070, Pittsburgh PA 15215. Dr. Cope has been the Director of the Pain Medicine Fellowship at the University of Pittsburgh Medical Center since the fall of 1997. Dr. Zhao leads the interventional pain management clinic at the VA Medical Center in Washington DC. Dr. Toshiwal is currently a Pain Medicine Fellow at the University of Pittsburgh Medical Center and may be contacted at grtosh@gmail.com
