Associations between insomnia and central sensitization in cancer survivors undergoing opioid therapy for chronic cancer pain: A STROBE-compliant prospective cohort study

Several risk factors for insomnia in cancer patients have been recognized, including chronic pain and treatment with opioid. Although associations between insomnia and central sensitization were previously reported in patients with chronic non-cancer pain, those have not been elucidated among cancer survivors undergoing opioid therapy for chronic cancer pain. To investigate the associations between insomnia and central sensitization among cancer survivors undergoing opioid therapy for chronic cancer pain, consecutive patients undergoing chemotherapy with chronic cancer pain under opioid therapy on an outpatient basis were enrolled from September 2019 to August 2020 and answered questions from the Athens Insomnia Scale (AIS) for assessing insomnia. Pain characteristics, including pain intensity, neuropathic pain, central sensitization assessed using the central sensitization inventory (CSI), opioid use disorder, and pain-related psychological symptoms were also examined. Uni- and multivariate regression analyses were performed to elucidate correlations between the AIS score and these pain characteristics. Of 44 enrolled patients, 20 patients completed to answer all questions. Insomnia was identified in 9 patients (45%). Although AIS scores showed no significant associations with pain intensity, neuropathic pain, opioid use disorder, or psychological symptoms, multivariate regression analysis revealed that CSI scores showed a positive relationship with AIS scores (P = .004). Discrimination was assessed using linear regression analysis which confirmed a significant association between the AIS and CSI scores (P = .002). Insomnia appears to be associated with central sensitization in cancer survivors with chronic cancer pain under opioid therapy.