Impact of psychological characteristics on spinal cord stimulation outcome

INTRODUCTIONReduced efficacy of spinal cord stimulation (SCS) may be attributed to technical factors, resulting in loss of target area paraesthesia and analgesic efficacy. It has been suggested that the impact of psychological factors should be taken into consideration when investigating SCS efficacy. A systematic review observed a lack of consistent evidence to suggest any particular psychological factors linked with SCS efficacy.1 Depression was suggested by the majority of the studies included in this review as a possible impacting factor; however it was concluded that successful treatment could modify the level of depression if it was a state in reaction to the pain rather than a trait characteristic. The most common psychological factor associated with the onset and continuation of chronic pain is catastrophising, alongside a lack of perceived internal control. It can therefore be hypothesised that certain psychological factors, specifically coping strategies may interact with the experience of pain and response to SCS. The aim of this prospective study was to identify psychological characteristics that may impact on the efficacy of SCS.METHODSSeventy-five patients were initially recruited and 56 patients (31 female and 25 male) were followed-up for 12-months. Outcome measures were assessed at baseline, six-months and 12-months following SCS implantation included visual analogue scale (VAS), Oswestry disability index (ODI), hospital anxiety and depression (HAD) scale and the pain coping strategies questionnaire (PCSQ).RESULTSStatistically significant improvements were observed for the VAS (p<0.001), ODI (p=0.011), anxiety (p=0.042), and depression (p=0.010) in the HAD scale and for the subscales reinterpreting pain sensation (p=0.018), control over pain (p=0.001), and ability to decrease pain (p<0.001) of the PCSQ. We observed that depression and autonomous coping (control over pain, ability to reduce pain, and catastrophizing) may impact sensory aspects such as pain intensity (Table 1) and disability scores affecting the outcome of SCS treatment. Age at time of implant and duration of pain prior to implant were also found to impact SCS efficacy.DISCUSSIONThere is good support for psychological factors affectingpain from both clinical work and neuroimaging, and also for SCS affecting pain at higher centers, including the anterior cingulate cortex. It is therefore reasonable to hypothesize that the pain relief achieved and psychological outcome are linked. Our focus was on constitutional psychological factors and their impact upon outcome. We can only conjecture as to the possible mechanisms. A neurochemical basis could explain less responsiveness due to greater diffuse noxious inhibitory control.CONCLUSIONPsychological characteristics such as depression and autonomous coping strategies may influence and predict the long-term efficacy of SCS. Also age at time of implant and duration of pain prior to implant were found to impact SCS outcome. Support for patients with low autonomous coping strategies and long-standing depression prior to implant may prove efficacious to long-term SCS outcome.REFERENCE1. Sparkes E, Raphael JH, Duarte RV, et al. Pain 2010; 150: 284-289.