Factors Predicting Long-Term Outcomes among Patients Treated with Spinal Cord Stimulation

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. Karen Julia Doblin Beth Israel Medical Center, USA