Background: While chronic pain has been said to impact patient’s response to methadone maintenance
treatment for opioid dependence, the reported findings are inconsistent. These discrepancies may be a direct result of
variations in the measurement of chronic pain or definitions of response to methadone treatment. The goal of this study is
to evaluate the association between pain and substance use behaviour to determine the real impact of comorbid pain in the
methadone population. We also aim to examine sources of variation across the literature with a specific focus on the
measurement of pain.
Methods/Design: We performed a systematic review using an electronic search strategy across CINAHL, MEDLINE,
Web of Science, PsychINFO, EMBASE, and the Cochrane Library including Cochrane Reviews and the Cochrane Central
Register of Controlled Trials databases. Title, abstract, as well as full text screening and extraction were performed in
duplicate. Studies evaluating the association between chronic pain and methadone maintenance treatment response were
eligible for inclusion in this review. Using a sample of 297 methadone patients from the Genetics of Opioid Addiction
(GENOA) research collaborative, we assessed the reliability of patient self-reported pain and the validated Brief Pain
Inventory (BPI) assessment tool.
Results: After screening 826 articles we identified five studies eligible for full text extraction, of which three showed a
significant relationship between the presence of pain and the increase in substance abuse among patients on methadone for
the treatment of opioid dependence. Studies varied largely in the definitions and measurement of both pain and response
to treatment. Results from our validation of pain measurement in the GENOA sample (n=297) showed the use of a simple
self-reported pain question is highly correlated to the use of the BPI. Simply asking patients whether they have pain
showed a 44.2% sensitivity, 88.8% specificity, 84.4% PPV and 53.6% NPV to the BPI. The area under the ROC curve
was 0.67 and the Pearson χ2 was 37.3; (p<0.0001).
Discussion: The field of addiction medicine is at a lack of consensus as to the real effect of chronic pain on treatment
response among opioid dependent patients. Whether it be the lack of a single “gold standard” measurement of response, or
a lack of consistent measurement of pain, it is difficult to summarize and compare the results of these relatively small
investigations. In comparison to the BPI, use of the simple self-reported pain has lower sensitivity for identifying patients
with pain, suggesting the inconsistencies in these studies may result from differences in pain measurement. Future
validation studies of pain measurement are required to address the predictive value of self-reported pain.