Evidence of specific cognitive deficits in patients with chronic low back pain under long-term substitution treatment of opioids.

BACKGROUND: There is a growing number of patients worldwide being treated with long-term opioids for chronic non-cancer pain, although there is limited evidence for their effectiveness in improving pain and function. Opioid-use related adverse effects, especially in cognitive functioning in these patients, are rarely evaluated.

OBJECTIVES: The present study investigated the cognitive functions of patients with chronic back pain who underwent long-term opioid treatment in comparison with those patients without opioid usage and healthy controls.

STUDY DESIGN: A prospective, nonrandomized, cross-sectional study.

SETTING: Multidisciplinary pain management clinic, specialty referral center, University Hospital in Germany.

METHODS: In a prospective cross-sectional design, 37 patients with chronic back pain who underwent long-term opioid therapy (OP) were compared with 33 patients with chronic back pain without opioid therapy (NO) and 25 healthy controls (HC). Assessment of primary outcome included cognitive function such as information processing speed, choice reaction time, pattern recognition memory, and executive function. Other data included pain, back function, depression and anxiety, use of medication, and education status. The relationship between cognitive functions and anxiety/depression was analysed.

RESULTS: Both patient groups needed significantly longer time in information processing when compared to HC (Group 1: 41.87 ± 20.47 Group 2: 38.29 ± 19.99 Group 3: 30.25 ± 14.19). Additionally, OP patients had significantly reduced spatial memory capacity, flexibility for concept change, and impaired performance in working memory assessment compared to NO patients and HC. The impaired cognitive outcomes were significantly associated with pain intensity, depression scores, and medication use.

LIMITATIONS: Limitations include small number of patients with heterogeneous opioid therapy and the nonrandomized observational nature of the study.

CONCLUSIONS: Our findings give a differential view into the cognitive changes from chronic back pain with and without long-term opioids treatment. Chronic back pain itself impairs some distinct cognitive functions. Long-term opioid therapy adds further cognitive impairment.