Pain
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Nociceptive primary afferents have the capacity to induce a state of increased excitability or central sensitization in dorsal horn neurones. This contributes to the mechanical hypersensitivity (allodynia) which occurs after peripheral tissue injury where low-mechanothreshold primary afferent activation begins to elicit pain. The relative susceptibility of dorsal horn cells with an apparent exclusive nociceptive input (nociceptive-specific (NS) or high-threshold (HT) cells) and those with a convergent input from low- and high-threshold mechanoreceptors (wide-dynamic-range (WDR) or multireceptive neurones) to sensitivity changes has been disputed. ⋯ In 3 cells, an increase in the response to A-fibre afferents occurred, a novel A-fibre response was recruited in 2 cells and the C-fibre response increased in 2 cells. Cells in the superficial dorsal horn of the rat spinal cord that are normally NS can begin, therefore, to respond to LT primary afferent mechanoreceptors after an increase in central excitability produced by activation of peripheral chemoreceptors. Sensitization of these, as well as of WDR cells, may contribute to the generation of post-injury mechanical pain and reflex hypersensitivity.
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Randomized Controlled Trial Clinical Trial
Long-term results of cervical epidural steroid injection with and without morphine in chronic cervical radicular pain.
To evaluate the long-term effectiveness of a single cervical epidural steroid injection (CESI) performed with or without morphine, 24 patients, without need of surgery, but suffering for more than 12 months from cervical radicular pain, were included in a prospective and randomised study. The cervical epidural space was injected (C7-D1; 18-ga needle) with an increasing volume (10 ml maximum) of isotonic saline solution to exacerbate the patient's radicular pain. The patients were then randomly allocated to 2 groups: the steroid group (group S, n = 14) received an equivalent volume of 0.5% lidocaine plus triamcinolone acetonide (10 mg/ml) and the steroid plus morphine group (group S + M, n = 10) received the same combination plus 2.5 mg of morphine sulphate. ⋯ Despite observing a better transient improvement the day after CESI in the S + M group, long-term results did not differ. The success rate was 78.5% in group S and 80% in group S + M providing pain relief of 86.8 +/- 14.7% and 86.9 +/- 17.9%, respectively. Pain relief remained stable with time (mean follow-up: 43 +/- 18.1 months).(ABSTRACT TRUNCATED AT 250 WORDS)
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A decrease in mechanical pressure pain thresholds, particularly over pre-designated tender points, is one of the defining characteristics of fibromyalgia syndrome (FS); however, changes in thermal pain sensitivity have not been investigated. The present study examined heat pain thresholds and cerebral event-related potentials following CO2 laser stimulation in 10 subjects with FS and 10 age-matched control volunteers. The results indicate that patients with FS exhibit a significant reduction in heat pain threshold when tested on the dorsal surface of the hand. ⋯ Patients with FS also displayed a significant increase in the peak-to-peak amplitude of the cerebral potential evoked by CO2 laser stimulation at pain threshold intensity and 1.5 times pain threshold intensity. These findings suggest a greater activation of central nervous system (CNS) pathways following noxious input. Putative explanations for the increased CNS response are discussed, including mechanisms of peripheral nociceptor sensitization, altered CNS function and the role of psychological factors.
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Nerve lesions producing extensive axonal loss can induce painful hyperalgesic states in man. The affect of axonal regeneration and end-organ reinnervation on hyperalgesia and pain is controversial. This study used two axonotmetic models, the sciatic crush injury (CI) and the sciatic chronic constrictive injury (CCI), to investigate the affects of nerve regeneration and reinnervation on hyperalgesia and presumed painful behavior in rats. ⋯ Motor function recovery occurred primarily over days 23-59 post-ligature. During this prolonged period of motor function recovery there was a resolution of the sciatic-mediated plantar surface heat hyperalgesia and the saphenous-mediated heat ANH. The above data support the hypothesis that the successful regeneration of distal axons after axonotmetic lesions can initiate the resolution of neuropathic hyperalgesia.
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Clinical Trial
The false-positive rate of uncontrolled diagnostic blocks of the lumbar zygapophysial joints.
One hundred and seventy-six consecutive patients with chronic low back pain and no history of previous lumbar surgery were studied to determine the false-positive rate of single diagnostic blocks of the lumbar zygapophysial joints. All patients underwent diagnostic blocks using lignocaine. Those patients who obtained definite or complete relief from these blocks subsequently underwent confirmatory blocks using bupivacaine. ⋯ Using the response to confirmatory blocks as the criterion standard, the false-positive rate of uncontrolled diagnostic blocks was 38% and the positive predictive value of these blocks was only 31%. Because the positive predictive value of a test is lower when the pre-test probability (prevalence) is low, and because the prevalence of lumbar zygapophysial joint pain is likely to be less than 50%, uncontrolled diagnostic blocks will always be associated with an unacceptably low positive predictive value. These features render uncontrolled diagnostic blocks unreliable for the diagnosis of lumbar zygapophysial joint pain not only in epidemiologic studies but also in any given patient.