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The response rate to conventional treatment among individuals with chronic pain is poor (Sachy, 2010). While 75% of patients with chronic pain sought medical care, only 56% reported good pain relief (Shi, Langer, Cohen, & Cleland, 2007). Implantable therapies, such as spinal cord stimulation (SCS) and intrathecal pain pumps, are used in the treatment algorithm when opioids and other therapies fail to produce adequate pain relief (Golovac, 2010; Meyerson & Linderoth, 2006). SCS, also referred to as dorsal column stimulation (DCS), is an implantable device involving the positioning of an electrode in the epidural space of the spinal cord at the level of the nerve roots innervating the painful area (Brook, Georgy, & Olan, 2009). An electrical current from the electrode brings about paresthesia, a sensation that suppresses pain (Kemler, Barendese, De Vet, Van den Wildenberg, & Van Kleef, 2006). The device itself uses no medication, making SCS an attractive alternative option for many patients since their pain is largely unresponsive to their present medication regimen (Casasola, 2010). This treatment modality offers patients with chronic intractable pain another way to increase functional ability and productivity and ultimately offers a chance to regain health and improve quality of life (QOL) (Kemler et al., 2006).
SCS can reduce pain levels by 50% or more, allowing decreases in pain medication in more than 60% of patients (Verilli, Mitchell, Vivian, & Sinclair, 2009). However, despite advances in surgical technique and system technology, 25% to 50% of patients who have undergone a successful screening process report loss of analgesia within 12 to 24 months of permanent implantation (Atkinson, Brooker, O’Callaghan, Salmon, Semple, & Majedi, 2011; Doleys, 2006).
Patient selection has been identified as the key to the long-term success with implantable therapies (Brook, Georgy, & Olan, 2009). The selection process is based on choosing patients with an underlying desire to get better and who also have etiologies that have been shown to benefit from SCS. The criteria for selection is usually based on several factors, including the exact pathology and type of pain generator, the amount of pain that is neuropathic, and the patient’s motivation and participation (Mekhail, Cheng, Narouse, Kapural, & Deer, 2010). Another very important factor is the timely application of therapy with the best results occurring within the first three years of the onset of pain (Mekhail et al., 2010).
Pain may become more established over time (Kumar, Wilson, Taylor, & Gupta, 2006) and the development of tolerance can be challenging for SCS long-term efficacy (Golovac, 2010; Kumar, Buchser, Linderoth, Meglio, & Van Buyten, 2007). However, long-term relief from implantable therapies may also be related to patient characteristics, such as educational level, age, type of pain, and sex (Atkinson et al., 2011; Doleys, 2006; Golovac, 2010). This article has the following objectives: a) Identify patient characteristics (age, sex, type of pain, and educational level) that may be predictive of long-term outcomes with SCS; b) Explain neuromodulation and its role in pain relief; c) Identify distinguishing features of neuropathic versus nociceptive pain; d) Identify the role of sex hormones in pain perception; and e) Explain the role of technology in interventional pain modalities.
Key Terms in this Chapter
Dorsal Column: The dorsal column gives rise to nerve roots, which are critical in pain transmission going from the spinal cord to the brain. The dorsal column is where injury, damage, and trauma become pain.
Complex Regional Pain Syndrome (CRPS): CRPS is defined as a clinical condition resulting from trauma to an area of the body. Four criteria are basic to the definition: diffuse pain not corresponding to the distribution of a peripheral nerve, diminished function of the affected area, stiffness of the involved joints, and characteristic skin and soft tissue changes, such as swelling, rubor, and warmth in the early stages to atrophy, stiffness, and coldness as the syndrome progresses ( Kumar et al., 1997 ).
Modulation: Modulation is the activation of descending pathways, which exert inhibitory effects on the cells responsible for pain transmission ( Moffat & Rae, 2010 ).
Nociception: Nociceptive pain involves normal processing of stimuli and is usually responsive to pain medications.
Plasticity (Neuroplasticity): Plasticity is the brain’s ability to reorganize itself by forming new neural connections throughout life. Neuroplasticity allows the neurons (brain cells) to compensate for injury and disease and to adjust their activities in response to new situations or changes in their environment (Latremoliere & Wolf, 2009 AU127: The in-text citation "Latremoliere & Wolf, 2009" is not in the reference list. Please correct the citation, add the reference to the list, or delete the citation. ; Apkarian, Hashmi, & Baliki, 2011 AU128: The in-text citation "Apkarian, Hashmi, & Baliki, 2011" is not in the reference list. Please correct the citation, add the reference to the list, or delete the citation. ).
Neuropathic Pain: Neuropathic pain syndromes include those in which normal pain pathways have been damaged, such as CRPS, radiculopathy, and peripheral neuropathies. Neuropathic pain is initiated when there is dysfunction or damage to the nervous system.
Dysthesia: Dysthesias are abnormal painful sensations produced by damage to nerve pathways usually in an area of sensory loss. Dysthesias are commonly described as ‘pins and needles,’ burning or tingling sensations.
Tolerance: Tolerance is defined as the gradual loss of pain relief for reasons not related to mechanical problems.
Allodynia: Allodynia occurs when a nonpainful stimulus is felt as painful in spite of normal-appearing tissues and is common in many neuropathic conditions.
Gate Control Theory of Pain: The Gate Control Theory of Pain explains the biological processes involved in pain perception. It uses three systems which interact to produce the pain response. Specialized cells in the spinal cord act as a gate control system that modulates the transmission of nerve impulse from peripheral fibers (body) to central cells (brain) (Melzack, 1965 AU126: The in-text citation "Melzack, 1965" is not in the reference list. Please correct the citation, add the reference to the list, or delete the citation. ).