Tactile acuity (dys)function in acute nociceptive low back pain: a double-blind experiment

Research shows that chronic pain is related to cortical alterations that can be reflected in reduced tactile acuity, but whether acute pain perception influences tactile acuity has not been tested. Considering the biological role of nociception, it was hypothesized that nociceptive pain will lead to a rapid improvement in tactile acuity and that this effect is correlated with pain intensity and pain distribution. In this randomised double-blind controlled experiment (trial no. NCT03021278), healthy participants were exposed to 1 of 3 experimental conditions: acute, nociceptive low back pain induced by saline injection, a sham injection (without piercing the skin) potentially inducing nocebo pain, or no intervention. Tactile acuity was measured by a battery of tests, including two-point discrimination threshold (TPD), before, during the pain experience, and after it subsided. We found that TPD did not improve but deteriorated during pain induction in the experimental group compared with the control group (P < 0.001; η = 0.20) and changed from 56.94 mm (95% confidence interval: 53.43-60.44) at baseline to 64.22 mm (95% confidence interval: 60.42-68.02) during the pain experience. Maximum reported pain was a significant predictor (β = 0.55, P = 0.01) and accounted for 26% of the variance in TPD (P < 0.05). Other tests, point-to-point test and two-point estimation task, changed with a similar trend but did not reach significance. We concluded that acute, nociceptive pain does not improve but deteriorates tactile acuity linearly. The biological role of the observed phenomenon is unknown, and therefore, future studies should address this question.