Pain
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Parietal, insular and anterior cingulate cortices are involved in the processing of noxious inputs and genesis of pain sensation. Parietal lesions may generate central pain by mechanisms generally assumed to involve the 'medial' pain system (i.e. medial thalamic nuclei and anterior cingulate cortex (ACC)). We report here PET and fMRI data in a patient who developed central pain and allodynia in her left side after a bifocal infarct involving both the right parietal cortex (SI and SII) and the right ACC (Brodmann areas 24 and 32), thus questioning the schematic representation of cortical pain processing. ⋯ Conversely, both PET and fMRI data argue in favour of plastic changes in the 'lateral discriminative' pain system. Particularly, allodynia was associated with increased activity anteriorly to the infarct in the right insula/SII cortex. This response is likely to be responsible for the strange and very unpleasant allodynic sensation elicited on the left side by a non-noxious stimulation.
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Perioral electrical stimuli cause inhibitory reflex responses in single motor-units (SMU) and surface electromyographic (EMG) recordings from voluntary contracted human jaw-closing muscles. Tonic experimental masseter pain has recently been shown to reduce the inhibitory reflex response in surface EMG recordings but the effect on SMU activity has not been described. In this study, motor-unit action potentials were recorded with wire electrodes inserted into the left masseter in eleven subjects. ⋯ Tonic masseter pain did not change pre-stimulus SMU firing characteristics but the mean ISI for the first post-stimulus discharge (158.2+/-9.2 ms) was significantly decreased compared to the pre-pain (175.8+/-11.3 ms, P<0.05) and post-pain conditions (172. 6+/-11.6 ms, P<0.05). The post-stimulus firing probability was significantly increased and the relative amplitude of the estimated IPSP significantly decreased during tonic masseter pain compared to pre-pain and post-pain conditions. In conclusion, this study indicates that tonic masseter pain has a net excitatory effect on the inhibitory jaw-reflexes, which could be mediated by presynaptic mechanisms on the involved motoneurons.
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Randomized Controlled Trial Clinical Trial
Intraarticular morphine versus dexamethasone in chronic arthritis.
Intraarticular morphine inhibits pain after knee surgery without overt toxicity. This study examined intraarticular morphine in chronic arthritis. We undertook a randomized double-blind comparison between intraarticular morphine (3 mg), dexamethasone (4 mg) and saline (3 ml) in 44 patients with chronic inflammatory arthritis or osteoarthritis of the knee. ⋯ No patient displayed untoward side effects. Synovial leukocyte counts were lower after morphine than after saline. In conclusion, intraarticular morphine produces analgesia of similar magnitude to dexamethasone and it may have antiinflammatory actions in chronic arthritis.