Treatment history and placebo responses to experimental and clinical pain in chronic pain patients.

BACKGROUND: Placebo analgesia refers to the reduction in pain due to the administration of an inert treatment. It is induced by expectations of pain relief which are enhanced by learning mechanisms. In healthy humans, prior positive experiences enhance the placebo response. However, the effects of patients' prior experiences with treatment on placebo responses have not yet been examined. This study investigated how verbal information, learning and treatment history influence the magnitude of placebo analgesia in chronic pain. METHODS: We administered a pharmacological placebo intervention in a sample of chronic pain patients (n = 49) who were seeking treatment in an outpatient pain clinic. Analyses were based on placebo responders. RESULTS: We found that verbal information about a potent pain-relieving effect of the intervention induced a large placebo analgesic response to both acute experimental (F(1,44) = 43.35, p < 0.001) and chronic pain (F(1,44) = 37.72, p < 0.001). However, the placebo responses to experimental and chronic pain were not significantly related (r = 0.012, p = 0.95). An additional conditioning procedure did not significantly enhance placebo analgesia. Treatment history modulated the magnitude of the placebo response: patients with a more negative pain-related treatment history reported significantly larger placebo responses to their own chronic pain (τ = 0.271, p = 0.044). CONCLUSIONS: We could show that placebo responses to both acute and chronic pain are high in pain treatment settings and that treatment history modulates this effect. Different mechanisms might underlie placebo responses to acute and chronic pain. Our findings highlight the necessity of considering placebo responses and treatment history in the treatment of chronic pain. WHAT DOES THIS STUDY ADD?: Placebo analgesia following verbal information of potent pain relief is high in chronic pain patients in a clinical setting. It is modulated by treatment history. Different mechanisms might underlie placebo analgesia to acute and chronic pain.

Suffering as an independent component of the experience of pain.

BACKGROUND: Pain has consistently been viewed as containing two dimensions, a sensory (intensity) and an emotional (unpleasantness). It has been suggested that pain involves higher order cognitive processes that go beyond unpleasantness. We therefore aimed at extending the assessment of pain by introducing an additional dimension of pain-related suffering and identifying noxious stimulation protocols that are most adequate for its psychophysical and psychophysiological characterization. METHODS: Twenty-four healthy volunteers received separate series of tonic and phasic noxious mechanical stimuli. Visual analogue scales were used to rate intensity, unpleasantness and suffering and psychophysiological measurements such as heart rate, skin conductance and corrugator electromyography were recorded. Acoustically evoked startle responses were measured in part of the assessments to obtain additional indicators of pain aversiveness. RESULTS: Spearman's correlation coefficients and partial correlations analyses as well as principal component analyses confirmed that suffering constitutes an integral component of pain processing that is distinct from intensity and unpleasantness. Tonic, rather than phasic, stimulation method was more effective in eliciting pain and suffering and under this condition startle responses where higher during long compared to short stimuli. CONCLUSIONS: These results suggest that in acute pain, suffering is a constitutive dimension that might even be more crucial in clinical states of pain.

D-amphetamine does not improve outcome of somatosensory training.

BACKGROUND: D-amphetamine has been shown to affect early stages of stroke recovery, and may have a beneficial effect on functions when administered later after stroke. OBJECTIVE: To test D-amphetamine effects on skill acquisition after the acute or subacute stages of stroke, when lesion-related structural changes have consolidated. METHODS: Sixteen healthy subjects were treated with D-amphetamine during a 4-week training of tactile frequency discrimination in a placebo-controlled, double-blind design. RESULTS: All subjects improved significantly in tactile temporal acuity. However, improvement did not differ in subjects treated with or without D-amphetamine. CONCLUSION: No beneficial effect of D-amphetamine on somatosensory training improvements was found in healthy subjects.