Neurostimulation in Chronic Pain Patients
Chronic pain, left untreated, produces a myriad of adverse physical and psychosocial effects. Often, chronic pain patients cannot work, and the preoccupation with pain can result in depression and a deterioration of family life. The estimated annual costs for chronic pain, including direct medical expenses, lost income, lost productivity, compensation payments, and legal charges are estimated to be fifty to one hundred billion dollars annually.1
Recalling the definition of pain developed by Margo McCaffery in 1968; “Pain is whatever the experiencing person says it is, existing whenever he says it does.”2 No matter what the cause, chronic pain—defined as persisting or recurring for more than six months—is real and unrelenting.
Treating chronic pain requires, at a minimum:
- Proper diagnosis along with the establishment of therapeutic goals. Physicians must evaluate the patient’s history, physical findings and diagnostic testing. The therapeutic goals must be realistic.
- The physician must expect and demand patient compliance with medication protocols along with active physical rehabilitation.3,4
However, even with highly motivated and compliant patients, there are many instances where treatment goals are not being achieved. The physician must be able to step back, re-evaluate treatment protocols and goals, treatment and compliance issues, and be willing to consider other treatments. These other treatments may require referral to other specialists, and may include:
- therapeutic nerve blocks
- surgical interventions
The goal of surgical intervention is to obtain pain relief by surgically removing a pain generating lesion, such as a mechanical spinal pathology that is verifiable by imaging and diagnostic nerve blocks. However, surgical (minimally invasive) intervention may also include implantable pain therapies such as neurostimulation and intrathecal drug delivery. Neurostimulation is a reversible therapy which can be tested prior to implantation.
Mode of Operation
Neurostimulation is a reversible, cost-effective method of pain relief that had been introduced in 1967 for patients with chronic, intractable pain of the trunk and limbs. It has been widely used since the 1970s. Since its introduction, both patient selection criteria and the devices have been continuously improved.3 Neurostimulation can be accomplished by both fully implantable and external radio-frequency powered systems. Some systems have multiple stimulating leads. External radio-frequency systems are indicated if the stimulation parameters required for pain control are too high for the battery of an implantable system. They are also the only systems approved for peripheral nerve stimulation.
Neurostimulation delivers low-voltage electrical stimulation to the spinal cord or peripheral nerves resulting in parasthesia of the area of pain. The procedure involves the implanting a lead or leads near the level of the spinal cord that corresponds to the area or areas of pain and is connected by an extension to an implanted device or an implanted receiver that is powered by an external transmitter.
For spinal cord stimulation (SCS), the screening test requires a temporary lead to be implanted at the spinal level corresponding to the area(s) of pain. This is attached to an external stimulator to validate the effectiveness of the proposed therapy. This test allows the patient to experience the effect of neurostimulation in controlling pain. It allows the patient to make an informed decision prior to pursuing the treatment.
Peripheral neurostimulation requires an anesthetic nerve block to determine if the pain is confined to a specific nerve branch. If the nerve branch(s) is involved, the screening test can continue prior to implanting the receiver.
A cost-effectiveness screening test should be performed prior to any implantation procedure. Generally, a screening test is considered successful if the patient experiences at least a fifty percent (50%) reduction in pain.5 The screening test is an approach to select the appropriate therapy and assure that patients do not submit to a surgical procedure that may not be effective.
Indications For Neurostimulation
Neurostimulation can play an important role in the treatment of chronic pain patients and has been shown to be a cost-effective intervention for difficult patients with chronic pain.5-7 When other treatments are either ineffective or no longer effective, neurostimulation can offer advantages in appropriately selected patients:
- reduced pain
- reduced need for opiate analgesics
- reduced side effects from opiate analgesics
- improved ability to perform activities8-10
Proper patient selection is extremely important. Patients should be evaluated based upon the following criteria:
- There is an objective basis for pain.
- Non-surgical intervention therapies (including oral medication) have failed.
- No untreated chemical dependency exists.
- Psychological clearance has been obtained.
- No contraindications to surgery or therapy are present (such as sepsis).
The origin and pattern of the patient’s pain helps guide the selection of the appropriate implantable therapy. In general, neurostimulation is indicated for aiding in the management of neuropathic pain and pain in the extremity. These would include:
- phantom limb or stump pain
- post-herpetic neuralgia
The implantable neurostimulator may also be very effective in:
- failed back syndrome
- complex regional pain syndrome (CRPS)
- painful neuropathies
Contraindications for Neurostimulation
Patients with significant untreated drug habituation problems, issues of secondary gain, or other obvious psychological problems are poor candidates for implantable neurostimulation therapy. Patients must also meet the diagnostic criteria for appropriate surgical interventions. A screening test should be performed for those patients who have received psychological clearance prior to the surgical implantable procedure.
Contra-indications to the use of neurostimulation devices are: