The cognitive impact of chronic low back pain: Positive effect of multidisciplinary pain therapy.

OBJECTIVES: Little is known about the affected cognitive problems in chronic low back pain patients. For this patient cohort research mostly focused on memory of pain, rather than cognitive difficulties related to pain. Chronic pain may be associated with specific (yet undefined) cognitive deficits that affect everyday behaviour. We set out to compare the cognitive function of patients with chronic low back pain (cLBP) in the course of multidisciplinary pain treatments before and after therapy.

METHODS: Thirty-three patients with cLBP and 25 healthy controls between 20 and 70 years were recruited into the study. The inclusion criteria for patients were: (1) a history of at least 12 weeks of chronic myofascial low back pain without radicular pain sensation before enrolment; (2) grade II and higher chronicity according to von Korff; (3) no opioid medication. The patients recruited had a mean pain duration of 7.13±7.16 years and reported a mean pain intensity of 6.62±2.04 (visual analogue score, VAS). Their mean back function according to the Funktionsfragebogen Hannover (FFbH, a questionnaire comparable with the Health Assessment Questionnaire) was 52.39±20.23%. At three time points (before therapy, 3 weeks and 6 months after therapy) the study subjects were assessed prospectively with a battery of visual memory tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB). These included choice reaction time (CRT), pattern recognition memory (PRM) and spatial span (SSP). In parallel, the Trail-Making Test (TMT-A, TMT-B) and the Wechsler Adult Intelligence Scale (WAIS-III) were used to evaluate intelligence and cognitive flexibility.

RESULTS: At the beginning of MDPT (T1), it took patients with cLBP significantly longer than HC to complete TMT-A (38.29±19.99s vs 30.25±14.19s, p=0.047) and TMT-B (72.10±26.98s vs 55.99±22.14s, p=0.034). There were no significant differences between patients and HC in CRT, PRM and SSP. Three weeks (T2) and 6 months (T3) after MDPT, TMT-A reaction time of patients significantly improved by 6.5s and 8.1ms (38.3 ±19.9s vs 31.8±12.3s, p=0.02 and 31.8±12.3s vs 30.2±8.9s, p=0.021, respectively). The patients' working memory was also better 6 months after MDPT (48.8±11.1% at T1, 51.2±11.9% at T2, 57.1±10.9% at T3, p=0.008). Significant correlations among pain, depression/anxiety, medication and neuropsychological tests were found.

CONCLUSIONS: These findings show that patients with cLBP have slowed speeds of information processing and working memory, but no alteration in attention and recognition memory. There are clearly interactions of cognitive function with pain, depression, anxiety, and medication. MDPT may improve the impaired cognitive function of patients with cLBP.

IMPLICATION: Health professionals should contemplate the results from this study when planning therapy strategies especially when prescribing pain medications such opioids to patients with chronic low back pain.