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

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Many patients with chronic pain will respond to a combination of physical therapy, oral medication and other conservative therapies. However, when non-interventional therapies lack effectiveness, oral analgesics cause intolerable side effects and further corrective surgeries fail to give adequate pain relief, intrathecal drug delivery (IDD) is an effective alternative.
General selection criteria for intrathecal drug delivery
As with neurostimulation, for IDD to be considered as a treatment option, patients should meet the following general selection criteria:
● There is an objective basis for the patientís 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
IDD has proven efficacy in patients with intractable nociceptive pain where other therapies have failed, for example when oral analgesics have not been effective or cause intolerable side-effects. IDD has been used to successfully treat FBSS patients where pain is predominantly in the lower back, in multiple sites, or of a dominant nociceptive nature. IDD has also been used in cases where neurostimulation or a neurostimulation trial was unsuccessful and in difficult cancer pain and visceral pain cases.

Patient selection for intrathecal drug delivery
As with neurostimulation, before a patient becomes a candidate for IDD, the patient should undergo a thorough evaluation, which should include both physical and psychological elements. In addition, all patients should undergo a trial procedure.

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.

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 effect 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 and better preparing the patient for the neuromodulation procedure. It can also aid in preventing unsuitable candidates from undergoing an invasive and costly procedure and in redirecting rejected candidates to more appropriate treatment programs.
Intrathecal drug delivery trial procedure
The IDD trial period consists of an initial titration period, followed by an evaluation period in the patientís home environment. Dose titration must be carried out in the hospital. For this, small intrathecal doses of medication are administered in a patient-controlled manner by the use of a patient-controlled analgesia pump. The patient can increase the dose until an acceptable level of pain relief is achieved. The aim of the titration period is to find an optimal balance between pain relief and prevention of the occurrence of side effects. Once an optimal dose is established, the patient is further tested on an outpatient basis. This permits the assessment of the efficacy of IDD in the patientís home, and provides important information on improvements in quality of life and daily functioning. Ideally, the trial period should last between 3 to 4 weeks.

Indications for Intrathecal drug delivery
IDD is perceived to be most effective for nociceptive pain. In general, IDD is indicated for:
● Chronic, intractable pain of malignant or non-malignant origin
● Nociceptive or mixed pain
● Stable or changing pain patterns
In addition, IDD may be indicated for patients with non-malignant, intractable pain that is unresponsive to other treatments, patients who have undergone an unsuccessful neurostimulation trial, or for patients who experience intolerable adverse events from systemic opioid treatment.

Table 1: Common indications for intrathecal drug delivery

Disorder Causes and characteristics
Chronic back or leg pain associated with Failed Back Surgery Syndrome (FBSS), when pain is of a dominant nociceptive nature* ● A broad term used to describe persistent, disabling pain in the leg and/or lower back that follows one or more corrective surgeries
● FBSS primarily of a nociceptive origin is the most frequently used indication for IDD
Complex regional pain syndromes (CRPS) ● CRPS refers to various painful conditions that can occur secondary to an injury
● CRPS with diffuse nociceptive pain and CRPS-associated dystonia are the most frequently used indications for IDD
● CRPS in cases where neurostimulation was unsuccessful may also be indicated for IDD
CRPS II ● An intensely unpleasant burning pain felt in a limb where there has been partial damage to the sympathetic and somatic sensory nerves
Cancer ● Any malignant tumor which arises from the abnormal or uncontrolled division of cells that then invade and destroys the surrounding tissues
Pancreatitis ● An inflammatory disease of the pancreas that involves permanent, progressive destruction of pancreatic tissue
● It causes chronic abdominal pain which is usually stabbing and burning in nature
Osteoarthritis ● A disease of joint cartilage, associated with secondary changes in the underlying bone, which may cause pain and impair the function of the affected joint
● It may result from trauma and is most common in those past middle age
● Commonly occurs in the hip, knee and thumb joints
● A rheumatic disease involving several to many joints, either together or in a sequence
● Causes pain, stiffness, swelling, tenderness and loss of function
● The loss of bony tissue, resulting in bones that are brittle and liable to fracture
● The chronic pain of osteoporosis is usually caused by fractures
● Common bone fractures include hip fractures, wrist fractures, and fractures of vertebrae (compression fractures)
● Characterized by pain in the lowermost segment of the spine with radiation of the lower sacral and perineal areas
● The condition usually occurs after a fall in which the patients falls on the coccyx
● 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 component, it can be effectively treated with either neurostimulation or IDD. **Neurostimulation using retrograde SCS is also used in this indication

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