Methods and Instruments to Evaluate Cognitive Function in Chronic Pain Patients: A Systematic Review.

Objective: We aimed to systematically review the methods and instruments used to evaluate cognitive function in chronic pain (CP) patients.

Methods: A sensitive search strategy was designed using five databases. Based on the objectives and methodology, we selected cross-sectional studies on adults with chronic non-cancer pain in which cognitive function was assessed using validated instruments. The characteristics of the subjects, control groups, and other variables that might affect cognitive function, and the instruments used, were extracted from each article.

Results: In the 42 articles identified, 53 instruments were used to assess cognitive function. Chronic pain criteria were defined in 83.3% of the articles and more than half (57.1%) included single diagnosis samples, with fibromyalgia being the most frequent studied (75%). Patients with prior cognitive impairment were excluded in 61.9% of the studies, and a control group was included in 64.3% of the studies. In most cases potential confounding variables were evaluated. More than 14% of the studies used self-report measures, and 73.8% used neuropsychological instruments, particularly for assessing attention (30%) and memory (27.5%). None of the instruments were specifically validated for pain patients and only five studies analyzed the psychometric properties of the instruments.

Conclusions: Various instruments and methods were used to assess cognitive function in CP patients, particularly fibromyalgia patients, but also other cohorts with well-defined CP. The instruments used had been validated, but not for pain populations, thus they require specific adaptation and validation to be used in CP patients. Certain recommendations are made in order to improve the evaluation of cognitive function in these patients.