C-tactile touch perception in patients with chronic pain disorders.

INTRODUCTION: Slow brushing over the skin activates C-tactile nerve fibers that transmit pleasant tactile experiences in healthy subjects, leading to an inverted U-shaped velocity dependence of ratings: C-tactile optimal stroking stimulations are rated as more pleasant than slower or faster stimulations. Chronic pain diseases such as postherpetic neuralgia (PHN) and complex regional pain syndrome show altered C-fiber innervation density, sensory loss, and pain sensitization. OBJECTIVES: We aimed to investigate whether C-tactile function is affected in painful conditions. METHODS: We assessed psychophysically C-tactile function and sensory perception thresholds in 16 patients with PHN, 19 patients with complex regional pain syndrome, and 22 healthy controls. RESULTS: Assessment of C-tactile function showed a significantly altered perceived pleasantness of CT stimulation between healthy controls and patients with chronic pain. In specific, tactile stimulation was perceived less pleasant on the affected and contralateral side when compared with controls. In patients with PHN, velocity-dependent pleasantness ratings could not be obtained, suggesting highly impaired C-tactile function with functional loss of pleasant touch perception. CONCLUSIONS: In conclusion, this is the first report of impaired C-tactile function in patients with PHN. Reduced pleasantness resulting from gentle touch can reflect defective C-fiber function or result from central nervous system effects in a chronic pain state.