Tactile discrimination, but not tactile stimulation alone, reduces chronic limb pain.

Chronic pain is often associated with reduced tactile acuity. A relationship exists between pain intensity, tactile acuity and cortical reorganisation. When pain resolves, tactile function improves and cortical organisation normalises. Tactile acuity can be improved in healthy controls when tactile stimulation is associated with a behavioural objective. We hypothesised that, in patients with chronic limb pain and decreased tactile acuity, discriminating between tactile stimuli would decrease pain and increase tactile acuity, but tactile stimulation alone would not. Thirteen patients with complex regional pain syndrome (CRPS) of one limb underwent a waiting period and then approximately 2 weeks of tactile stimulation under two conditions: stimulation alone or discrimination between stimuli according to their diameter and location. There was no change in pain (100 mm VAS) or two-point discrimination (TPD) during a no-treatment waiting period, nor during the stimulation phase (p > 0.32 for both). Pain and TPD were lower after the discrimination phase [mean (95% CI) effect size for pain VAS = 27 mm (14-40 mm) and for TPD = 5.7 mm (2.9-8. ), p < 0.015 for both]. These gains were maintained at three-month follow-up. We conclude that tactile stimulation can decrease pain and increase tactile acuity when patients are required to discriminate between the type and location of tactile stimuli