Anatomy and Physiology of Pain Principles of Pain Spinal Cord Stimulation Intrathecal Drug Delivery Selective Spinal Cord Lesioning Neuroanesthesia

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bullet Many patients with chronic pain will respond to a combination of physical therapy, oral medication and other conservative therapies. Some will need surgical intervention to address the mechanical condition causing the pain, while others may require advanced interventions. Neurostimulation is an
effective alternative to destructive procedures or more costly spinal surgeries in selected patients.
bullet General selection criteria for neurostimulation
For neurostimulation to be considered as a treatment option, patients should meet the following general selection criteria:
● There is an objective basis for the patient’s pain complaint
● The patient is psychologically competent and has no psychological contraindications
● Further corrective surgeries are likely to produce complications or poor outcomes
● More-conservative therapies have failed to relieve pain or have caused intolerable adverse events
● No contraindications to surgery exist (e.g. sepsis, coagulopathy)
● No untreated chemical dependency exists
● Neurostimulation and IDD are not contraindicated
Neurostimulation is considered as the treatment of choice for patients with chronic back and leg pain frequently associated with FBSS whose pain manifests despite anatomically successful surgery, and for the treatment of patients with CRPS who are unsatisfactorily controlled on existing therapies.
Neurostimulation has also proved effective in difficult-to-treat populations where other therapies have failed.
bullet Patient selection for neurostimulation
Before a patient becomes a candidate for neurostimulation, the patient should undergo a thorough evaluation, which should include both physical
and psychological elements. In addition, all patients should undergo a trial procedure.
bullet Physical evaluation
A comprehensive history and physical examination of the patient should be completed to ensure that there is an objective basis for the pain. A complete pain history includes a general medical history with emphasis on the chronology and symptomatology of the pain. These data should include information about the onset, quality, intensity, distribution, duration, course and affective components of the pain, and details about exacerbating and relieving factors. The physical examination should also include an appropriate neurological and musculoskeletal evaluation. The effects of pain, as well as the causes of pain, should be evaluated and recorded. In addition, the physician should determine the pain type, pain pattern, and sources of pain. Determination of such pain characteristics allows the physician to select the appropriate therapy.
bullet Psychological evaluation
Most physicians agree that before considering a neuromodulation procedure, the patient should be assessed by a psychiatrist or a psychologist to rule out any psychological issues that may affect the therapeutic outcome. This psychological evaluation should take place in the early phase of the patient selection procedure.
A carefully performed psychological evaluation will have several benefits including, identifying those patients most likely to benefit from neuromodulation procedures, better preparing the patient for the neuromodulation procedure, and setting realistic expectations. It can also aid in preventing unsuitable candidates from undergoing an invasive and costly procedure and redirecting rejected candidates to more appropriate treatment programs.
bullet Neurostimulation trial procedure
Conducting a test stimulation before ‘permanent implantation’ allows patients and the pain management team to test neurostimulation for both efficacy and paraesthesia perception, which sometimes cannot be tolerated despite good pain relief. There is no consensus on either the technical approach or the length of the SCS trial. In addition, whether the trial should be carried out in hospitalized patients or on an outpatient basis is a matter of personal opinion, since there are no data to support any specific recommendations.
The criteria for a successful trial include at least a 50% reduction in pain intensity and in those centers able to measure it, a decrease in analgesic intake and a significant functional improvement. Patients that show substantial improvements in these parameters can be considered for a permanent implantation.
bullet Indications for neurostimulation
There is a large pool of evidence supporting the beneficial effects of neurostimulation. In general, neurostimulation is most effective for neuropathic pain, typically when the pain is of non-malignant origin (i.e. pain from a source other than cancer). Neurostimulation is CE marked for:
● Chronic, intractable pain of the trunk or limbs
● Neuropathic pain
● Stable pain patterns
Neurostimulation may also be used when other therapy methods are contraindicated. For example, neurostimulation may be indicated for patients for whom spinal surgery is contraindicated and for patients who may not fully profit from reoperation.
Table 1: Common indications for neurostimulation
Disorder Causes and Characteristics
Chronic back or leg pain associated with Failed Back Surgery Syndrome (FBSS), especially when pain is of a dominant neuropathic nature* ● A broad term used to describe persistent, disabling pain in the leg and/or lower back that follows one or more corrective back surgeries
● Commonly caused by injury to spinal structures, especially those of the lumbar spine
● Many patients develop their original pain from a ruptured disc, however the ensuing chronic pain is often a result of subsequent surgical procedures that cause scar tissue build up and/or neural damage
● FBSS of primarily neuropathic origin is the best indication for neurostimulation
Complex regional pain syndrome (CRPS) Type I (Also called reflex sympathetic dystrophy) ● CRPS refers to various painful conditions that can occur secondary to an injury
● CRPS Type I develops in response to a noxious event (non-nerve injury) e.g. muscle sprain, bone fracture
● Potential causes include repetitive trauma, stroke, myocardial infarction (heart attack) and excessive strain
● The pain symptoms are complex, diffuse, disproportionate to the original injury and worsen in response to limb pressure
Complex regional pain syndrome (CRPS) Type II (Also called causalgia) ● CRPS II develops in response to a nerve injury, usually to large nerves such as the median or sciatic nerve
● The pain is similar to that in CRPS Type I, however patients with Type II may also experience a formerly painless stimulus as painful, or may be hypersensitive to a stimulus, often in a hand or foot
Refractory angina ● Angina that is no longer treatable by surgical or medical intervention is known as refractory angina
● Angina is a recurring pain or discomfort in the centre of the chest that occurs when the heart’s need for oxygen increases beyond the oxygen available from the blood nourishing the heart
● It is a common symptom of coronary heart disease, which occurs when vessels that carry blood to the heart become narrowed and blocked due to atherosclerosis
● Physical exertion is the most common trigger for angina. Other triggers can be emotional stress, extreme cold or heat, heavy meals, alcohol and cigarette smoking
Peripheral vascular disease ● Caused by atherosclerotic plaque that causes the internal lining of the arteries to thicken; blood vessels become increasingly restricted and blood flow diminishes
● The most commonly affected peripheral areas are the arteries in the legs, arms, kidneys and neck
● Symptoms include dull cramping pain in the hips, thighs or calf, numbness or tingling in the legs, feet and toes, and changes in skin temperature
Postherpetic neuralgia (PHN) ● A serious, painful complication of herpes zoster, an infectious disease
● Pain is characterized by constant burning, aching sensations and episodes of ‘shooting-like’ electrical pain
Diabetic neuropathy ● A nerve disorder caused by diabetes mellitus
● It is characterized by a loss or reduction of sensation in the feet, and in some cases the hands, and by pain and weakness in the feet.
Phantom limb pain ● A painful sensation that an amputated limb is still present
● The syndrome is often associated with a painful sensation, such as burning, pricking, tickling or tingling
Spinal stenosis ● A narrowing of the spaces in the spine resulting in pressure on the spinal cord and/or nerve roots
● Pressure on the lower part of the spinal cord or on nerve roots branching out from that area may give rise to
pain or numbness in the legs
● Pressure on the upper part of the spinal cord (neck) produces similar symptoms in the shoulder
*FBSS pain that is primarily nociceptive responds to IDD. However, as most FBSS pain comprises nociceptive and neuropathic components, it can be effectively treated with either neurostimulation or IDD.

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