Pain
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Comparative Study
Use of a novel thermal operant behavioral assay for characterization of orofacial pain sensitivity.
Orofacial pain has been well-characterized clinically, but evaluation of orofacial pain in animals has not kept pace. The objective of this study was to describe behavioral responses to facial thermal stimulation and inflammation with/without an analgesic using a novel operant paradigm. Animals were trained to voluntarily place their face against a stimulus thermode (37.7-57.2 degrees C) providing access to positive reinforcement. ⋯ These outcomes were significantly affected in the direction of increased nociception following inflammation, and these indices of hyperalgesia were reversed with morphine administration. These data reflect an orofacial pain behavior profile that was based on an animal's responses in an operant escape paradigm. This technique allows evaluation of nociceptive processing and modulation throughout the neuraxis.
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Thirty-four patients with various forms of neuropathic pain have been examined with respect to two parameters of dynamic mechanical allodynia: the effect of repetitive stimulation on pain intensity; and refractory period. Pain intensity increased with repetitive stimulation ('windup') in most patients with neuropathic pain of peripheral origin, while it was not observed in patients with central neuropathic pain. While a non-responsive period occurs after tactile allodynic elicitation in patients with trigeminal neuralgia (Kugelberg and Lindblom, 1959), it was not seen in any case of neuropathic pain, including trigeminal neuropathy. The findings have implications for diagnosis, and require pathophysiological elucidation in terms of revealed differences.
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Randomized Controlled Trial Comparative Study Clinical Trial
Duloxetine vs. placebo in patients with painful diabetic neuropathy.
The aim of this study was to examine the efficacy and safety of duloxetine, a balanced and potent dual reuptake inhibitor of serotonin and norepinephrine, in the management of diabetic peripheral neuropathic pain. Serotonin and norepinephrine are thought to inhibit pain via descending pain pathways. In a 12-week, multicenter, double-blind study, 457 patients experiencing pain due to polyneuropathy caused by Type 1 or Type 2 diabetes mellitus were randomly assigned to treatment with duloxetine 20 mg/d (20 mg QD), 60 mg/d (60 mg QD), 120 mg/d (60 mg BID), or placebo. ⋯ Significantly more patients in all three active-treatment groups achieved a 50% reduction in the 24-h Average Pain Score compared with placebo. Duloxetine treatment was considered to be safe and well tolerated with less than 20 percent discontinuation due to adverse events. Duloxetine at 60 and 120 mg/d was safe and effective in the management of diabetic peripheral neuropathic pain.
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Comparative Study
Qualitative and quantitative characterization of the thermal grill.
Concurrent applications to the skin of spatially adjacent bands of innocuous warm and cool stimuli would elicit a peculiar sensation, known as the 'thermal grill illusion'. To validate the thermal grill as a research tool, this two-phase study qualitatively characterizes this peculiar sensation and further quantitatively establishes the temperature matching of the most intense/noxious thermal grill stimulations at two different time points. The temperature combinations (degrees C) tested were: 18/18, 42/42, 18/42, 20/20, 40/40, 20/40, 22/22, 38/38, 22/38, 24/24, 36/36 and 24/36. ⋯ At the 3-second time point, the matching temperatures (+/-SD) of 20/40 and 18/42 were 45.7+/-1.8 (range 44-48) and 46.6+/-1.5 (range 44-48) degrees C, respectively, whereas the matching temperatures for the single temperature combinations were similar to the set temperatures. Importantly, at the 10-second time point, none of the combinations were significantly greater than the highest of the pair of stimuli. The time course variation in the perception of the combined stimuli suggests an adaptation occurred in central processing.