Distraction by a cognitive task has a higher impact on electrophysiological measures compared with conditioned pain modulation.

BACKGROUND: Conditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS). Using painful cutaneous electrical stimulation (PCES) as TS and painful cold water as CS, the pain relief was paralleled by a decrease in evoked potentials (PCES-EPs). We now aimed to compare the effect of CPM with cognitive distraction on PCES-induced pain and PCES-EP amplitudes. METHODS: PCES was performed using surface electrodes inducing a painful sensation of 60 (NRS 0-100) on one hand. In a crossover design healthy subjects (included: n = 38, analyzed: n = 23) immersed the contralateral hand into 10 °C cold water (CS) for CPM evaluation and performed the 1-back task for cognitive distraction. Before and during the CS and 1-back task, respectively, subjects rated the pain intensity of PCES and simultaneously cortical evoked potentials were recorded. RESULTS: Both CPM and cognitive distraction significantly reduced PCES-EP amplitudes (CPM: 27.6 ± 12.0 µV to 20.2 ± 9.5 µV, cognitive distraction: 30.3 ± 14.2 µV to 13.6 ± 5.2 µV, p < 0.001) and PCES-induced pain (on a 0-100 numerical rating scale: CPM: 58 ± 4 to 41.1 ± 12.3, cognitive distraction: 58.3 ± 4.4 to 38.0 ± 13.0, p < 0.001), though the changes in pain intensity and PCES-amplitude did not correlate. The changes of the PCES-EP amplitudes during cognitive distraction were more pronounced than during CPM (p = 0.001). CONCLUSIONS: CPM and cognitive distraction reduced the PCES-induced pain to a similar extent. The more pronounced decrease of PCES-EP amplitudes after distraction by a cognitive task implies that both conditions might not represent the general pain modulatory capacity of individuals, but may underlie different neuronal mechanisms with the final common pathway of perceived pain reduction.

Conditioned pain modulation using painful cutaneous electrical stimulation or simply habituation?

BACKGROUND AND AIMS: Cold pressor test was recently reported to significantly reduce painful cutaneous electrical stimulation (PCES)-induced pain and corresponding evoked potentials (PCES-EPs), but whether this reduction is an effect of conditioned pain modulation (CPM) remains unknown. To what extent these findings are confounded by habituation is also unknown. We thus compared the effect of CPM and habituation on PCES-induced pain and PCES-EPs and analysed whether increased attention by a random change of electric stimulation would intensify this possible habituation effect. METHODS: Three custom-built concentric surface electrodes were used to induce a pain intensity of 60 on a 0-100 numerical rating scale (NRS) among 29 healthy subjects (age 20-35y, 16 females). PCES-EPs (including P0N1 and N1P1 amplitudes, N1 latencies) were assessed over Cz. Group A received 14 min of electrical stimulation with constant intensity followed by 14 min of electrical stimulation with variable intensities, group B vice versa. Afterwards, subjects perceived cold-water pain (10 °C) contralaterally as conditioning stimulus to assess CPM. Statistical analysis was conducted with ANOVA and t-test. RESULTS: In both groups, N1 latencies remain unchanged, but the intensity of PCES-induced pain (12 ± 17%; p < 0.01) and N1P1 amplitudes of PCES-EPs (10 ± 16%; p < 0.05) decreased significantly during the 14-min PCES with constant current intensity. CPM also significantly reduced pain ratings (36 ± 19%; p < 0.001) and amplitudes (37.2 ± 15.8%), p < 0.001). A significant decline of P0N1 amplitudes occurred only during CPM (18 ± 61%; p < 0.001). CONCLUSION: We found a significant effect of habituation on PCES-induced pain and PCES-EPs, although the effect of CPM was significantly larger and could not be explained by habituation alone. SIGNIFICANCE: Painful cutaneous electrical stimulation leads to moderate habituation of pain and evoked potential amplitudes, but the conditioned pain modulation effect using this method is significantly larger, which might indicate a different mechanism in central processing.

Bilateral somatosensory cortex disinhibition in complex regional pain syndrome type I.

OBJECTIVE: In a previous study, we found bilateral disinhibition in the motor cortex of patients with complex regional pain syndrome (CRPS). This finding suggests a complex dysfunction of central motor-sensory circuits. The aim of our present study was to assess possible bilateral excitability changes in the somatosensory system of patients with CRPS. METHODS: We measured paired-pulse suppression of somatosensory evoked potentials in 21 patients with unilateral CRPS I involving the hand. Eleven patients with upper limb pain of non-neuropathic origin and 21 healthy subjects served as controls. Innocuous paired-pulse stimulation of the median nerve was either performed at the affected and the unaffected hand, or at the dominant hand of healthy controls, respectively. RESULTS: We found a significant reduction of paired-pulse suppression in both sides of patients with CRPS, compared with control patients and healthy control subjects. CONCLUSION: These findings resemble our findings in the motor system and strongly support the hypothesis of a bilateral complex impairment of central motor-sensory circuits in CRPS I.

[Pain in the left hand especially pronounced in the ring finger and small finger]. / Schmerzen der linken Hand mit Betonung am Ring- und Kleinfinger.

A case is described of a female patient, who presented with permanent stabbing and burning pain in the ring finger and small finger of the left hand. Because of this pain neurolysis of the sulcus ulnaris had been carried out 4 months previously, which did not result in an improvement but led to a spreading of the symptoms to the whole hand. Diagnostic three-phase skeletal scintigraphy and neurography were performed. In 1999 breast cancer was diagnosed and surgically treated. Oncological follow-up 2 months before presentation revealed no conspicuous findings.Readers are encouraged to make their own diagnosis on the basis of the clinical findings and to discuss the case online (http://blogs.springer.com/DerSchmerz).

Repetitive training of a synchronised movement induces short-term plastic changes in the human primary somatosensory cortex.

The aim of our study was to assess possible short-term plastic changes in the human primary somatosensory cortex (S1) induced by a repetitive synchronised movement of the right thumb and shoulder. We therefore performed a source localisation of somatosensory evoked potentials after median nerve stimulation in twelve healthy subjects before and after 1 h of motor training. We found a significant medial shift of the N20 dipole on the left hemisphere after training, whereas the dipole location on the right hemisphere remained unchanged. However, no significant correlation was seen between the dipole shift and the improvement in motor performance. We conclude that repetitive synchronised movements are able to induce plastic changes in the contralateral S1, which might be mainly due to the synchronised proprioceptive input.