Psychophysical tests as predictors of back pain chronicity in primary care.

UNLABELLED: If persons at risk of developing chronic pain could be identified early in a pain episode, treatment could be tailored on the basis of risk. Responses to psychophysical tests differ in persons with chronic pain vs pain-free controls and thus appear promising as indicators of susceptibility to chronic pain. In a cohort of 157 patients making their first primary care visit during a back pain episode, we explored the relationships of psychophysical test responses (pressure pain thresholds at low back and thenar sites, cold pressor pain ratings, conditioned pain modulation, and mechanical temporal summation) to baseline measures of pain and psychological distress and assessed whether test responses predicted clinically significant back pain 4 months later. Examiner-standardized pressure pain thresholds were significantly (P < .05) correlated with baseline back pain severity and diffuseness of bodily pain (Pearson correlations = -.21 to -.35). Lower baseline pressure pain thresholds significantly predicted back pain at 4 months (odds ratio [95% confidence interval]: low back, .66 [.44, .96]; thenar, .62 [.40, .92]); however, after controlling for participant age and sex, these associations were no longer significant. Cold pressor pain, conditioned pain modulation, and mechanical temporal summation were not significant predictors of 4-month back pain in either model. PERSPECTIVE: Some psychophysical test responses have been found to differ in persons with chronic pain vs pain-free controls. In this prospective study, psychophysical test responses had limited utility for predicting which primary care back pain patients would have clinically significant chronic pain 4 months later.