Abstract
The comorbidity of chronic pain and opioid addiction is a serious problem that has been growing with the practice of prescribing opioids for chronic pain. Neuroimaging research has shown that chronic pain and opioid dependence both affect brain structure and function, but this is the first study to evaluate the neurophysiological alterations in patients with comorbid chronic pain and addiction. Eighteen participants with chronic low back pain and opioid addiction were compared with eighteen age- and sex-matched healthy individuals in a pain-induction fMRI task. Unified structural equation modeling (SEM) with Lagrange multiplier (LM) testing yielded a network model of pain processing for patient and control groups based on 19 a priori defined regions. Tests of differences between groups on specific regression parameters were determined on a path-by-path basis using z-tests corrected for the number of comparisons. Patients with the chronic pain and addiction comorbidity had increased connection strengths; many of these connections were interhemispheric and spanned regions involved in sensory, affective, and cognitive processes. The affected regions included those that are commonly altered in chronic pain or addiction alone, indicating that this comorbidity manifests with neurological symptoms of both disorders. Understanding the neural mechanisms involved in the comorbidity is crucial to finding a comprehensive treatment, rather than treating the symptoms individually.
Highlights
There is a high prevalence of comorbid chronic pain and opioid addiction, presenting a serious healthcare challenge that has become an epidemic in the United States (Rosenblum et al, 2003; Clark et al, 2008; Barry et al, 2013; Salsitz, 2016)
X2-test of overall model fit; df, degrees of freedom; p, probability level; CF, comparative fit index; RMSEA, root mean square error of approximation; Stability Index is a measure of system stability in a non-recursive structural equation model (Fox, 1980; Bentler and Freeman, 1983)
There were some connection strengths that were greater in controls than patients, as indicated by a negative z-score, effect sizes for these comparisons were small (q ≤ 0.21 for all conditions, q ≤ 0.19 for pain condition only)
Summary
There is a high prevalence of comorbid chronic pain and opioid addiction, presenting a serious healthcare challenge that has become an epidemic in the United States (Rosenblum et al, 2003; Clark et al, 2008; Barry et al, 2013; Salsitz, 2016). Chronic pain is positively associated with substance use disorder severity, psychiatric disorders, psychological distress, medical comorbidities, general physical health problems, medical care utilization, and poorer psychosocial function (Jamison et al, 2000; Rosenblum et al, 2003; Potter et al, 2004; Trafton et al, 2004; Arnow et al, 2006; Tunks et al, 2008; Dominick et al, 2012; Burke et al, 2015; Howe et al, 2015). These comorbid factors are associated with relapse into substance use (Potter et al, 2010) and poor treatment outcomes
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