C-tactile touch perception in patients with chronic pain disorders

Abstract

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.

Keywords: C-tactile fibers; Neuropathic pain; Pleasant touch; Postherpetic neuralgia.

Figure 1.

Perceived quality of stroking in dependence of test side and group. One dot represents the rating of one individual per test side and velocity. Ratings are averaged over the 3 repetitions of velocity and rounded for visualization purpose. Significant effects are highlighted by asterisk, y-axis shows values of perceived pleasantness, intensity, and pain on visual analogue scales for pleasantness (−10 to 10: very unpleasant to very pleasant), intensity (0–10: not at all intense to very intense), and pain (0–10: not at all painful to very painful).

Figure 2.

Perceived pleasantness of stroking in relation to the stroking velocity. Group averaged ratings are presented for each test side and group. Effect sizes of the quadratic term are indicated and significant effects are highlighted by asterisk. Error bars indicate the 95% confidence interval, y-axis shows values of perceived pleasantness on a visual analogue scale for pleasantness (−10 to 10: very unpleasant to very pleasant). CRPS, complex regional pain syndrome; PHN, postherpetic neuralgia.

Figure 3.

Z-transformed QST data of patients with PHN and CRPS on the contralateral and affected test side. Z-values are displayed on the y-axis, the dashed lines indicate the range of 2 SD above/below the mean normative values as indicated in the manual. Each patient is visualized with one color. Z-values were calculated in reference to the individual sex, age, and location. To represent “gain of function” and “loss of function,” the Z-scores for CDT, WDT, TSL, HPT, PPT, MPT, and MDT were multiplied by (−1) (Rolke et al. 2006). Reference values were taken from the following studies: Pfau DB et al. (2014). Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): reference data for the trunk and application in patients with chronic postherpetic neuralgia. PAIN 155:1002–1015 and Rolke R, et al. (2006). Quantitative sensory testing in the German Research Network on Neuropathic Pain (DFNS): standardized protocol and reference values. PAIN 123:231–243.^, CDT, cold detection threshold; CRPS, complex regional pain syndrome; HPT, heat pain threshold; MDT, mechanical detection threshold; MPT, mechanical pain threshold; PHN, postherpetic neuralgia; PPT, pressure pain threshold; QST, quantitative sensory testing; TSL, thermal sensory limen; WDT, warm detection threshold.

Figure 4.

Dynamic mechanical allodynia (DMA) and paradoxical heat sensations (PHSs) of patients with PHN and CRPS on the contralateral and affected test side. Raw values are displayed, PHSs are displayed as occurrence of 3 tests, and PHS is only displayed for patients with pain on the trunk and feet. PHS values were multiplied by (−1) according to the concept that PHS represent a loss of thermodiscriminative function (Rolke et al. 2006). CRPS, complex regional pain syndrome; PHN, postherpetic neuralgia.