Pain
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This in-depth study examines the relationships between patient, stimulator and outcome variables in a large number of chronic pain patients utilising TENS on a long-term basis. 179 patients completed a TENS questionnaire designed to record age, sex, cause and site of pain and TENS treatment regime. Of these 179 patients, 107 attended our research unit for assessment of the electrical characteristics of TENS during self-administered treatment. Although a remarkable lack of correlation between patient, stimulator and outcome variables was found to exist, the analysis revealed much information of importance: 47% of patients found TENS reduced their pain by more than half; TENS analgesia was rapid both in onset (less than 0.5 h in 75% patients) and in offset (less than 0.5 h in 51% patients); one-third of patients utilised TENS for over 61 h/week; pulse frequencies between 1 and 70 Hz were utilised by 75% of patients; 44% of patients benefitted from burst mode stimulation. The clinical implications of these findings are discussed.
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Repetitive stimulation of small diameter primary afferent fibres produces a progressive increase in action potential discharge (windup) and a prolonged increase in the excitability of neurones in the spinal cord following the stimulus. Previous studies have demonstrated that windup is the consequence of the temporal summation of slow synaptic potentials and that the slow potentials and windup are reduced by pretreatment with N-methyl-D-aspartic acid (NMDA) antagonists. We have now examined whether primary afferent induced hypersensitivity states in flexor motoneurones are also dependent on the activation of NMDA receptors and whether windup is a possible trigger for the production of the central hypersensitivity. ⋯ When the the MK-801 and the D-CPP were administered once a state of central facilitation had been induced by prior treatment with mustard oil, they returned the facilitated reflex to its pretreatment level. These results indicate that NMDA receptors are involved in the induction and maintenance of the central sensitization produced by high threshold primary afferent inputs. Because central sensitization is likely to contribute to the post-injury pain hypersensitivity states in man, these data have a bearing both on the potential role of NMDA antagonists for pre-emptive analgesia and for treating established pain states.
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In a prospective open study we tested the Edmonton injector (EI), a device designed by our group for subcutaneous injection of narcotics. In 25 patients, the EI was used for patient-controlled analgesia (PCA); mean duration of treatment was 28 +/- 10 days. Mean equivalent daily dose of morphine was 160 +/- 85 mg. ⋯ Narcotics were administered every 4 h and extra doses were administered on a 'PRN' basis. Waiting time for a 'PRN' dose in 8 patients before starting the EI was 18 +/- 7 min; after the EI was started, it was 3 +/- 4 min (P less than 0.01). We conclude that the EI is safe, effective and inexpensive, and that it will be particularly useful in smaller hospitals and developing countries.
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Spinal cord stimulation has evolved over the past 20 years into an easily implemented technique, with low morbidity, for the treatment of intractable, chronic pain in properly selected patients. We report our experience with a series of 62 patients implanted between 1983 and 1987, with percutaneous and laminectomy electrodes, and with single- and "multi-channel" (programmable, multi-contact) devices. Fifty had chronic, intractable low back and leg pain ("failed back surgery syndrome," lumbar arachnoid fibrosis), five had spinal cord injuries, and seven "peripheral" pathology or stump pain. ⋯ Univariate and multivariate analysis of patient characteristics and technical factors as predictors of outcome demonstrated significant advantages for female patients, and for patients implanted with "multi-channel" devices. With these devices, electrode geometries with central cathode(s) flanked by rostral and caudal anode(s) were favored disproportionately. Technical improvements in implanted spinal cord stimulation devices, in particular the development of multi-contact percutaneous electrode arrays and supporting programmable electronics, have significantly improved clinical results.
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Comparative Study
A comparison of two-point discrimination threshold of tactual, non-painful stimuli between chronic low back pain patients and controls.
Differences in pain sensitivity between chronic pain patients and healthy controls have been reported. Seltzer and Seltzer extended this line of research in studying the sensitivity to non-painful stimuli. They reported that the 2-point discrimination threshold of chronic pain patients was higher than that of control subjects. ⋯ Therefore, in the present study we tried to replicate the findings in a group of chronic low back pain patients using a design that was believed to be methodologically stronger. Replication failed: no evidence was found for the hypothesis that chronic pain patients are less sensitive to non-painful stimuli. Further studies on various defined types of acute and chronic pain patients are required.