Pain
-
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.
-
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.
-
The communication of pain requires a sufferer to encode and transmit the experience and an observer to decode and interpret it. Rosenthal's (1982) model of communication was applied to an analysis of the role of facial expression in the transmission of pain information. Videotapes of patients with shoulder pain undergoing a series of movements of the shoulder were shown to a group of 5 judges. ⋯ The results indicated that although observers can make coarse distinctions among patients' pain states, they (1) are not especially sensitive, and (2) are likely to systematically downgrade the intensity of patients' suffering. Moreover, observers appear to make insufficient use of information that is available in patients' facial expression. Implications of the findings for pain patients and for training of health-care workers are discussed as are directions for future research.
-
Comparative Study
Spinal nociceptive transmission in the spontaneously hypertensive and Wistar-Kyoto normotensive rat.
Background and noxious heat-evoked responses of wide-dynamic-range (WDR) and high-threshold (HT) lumbosacral spinal dorsal horn neurons were recorded in spontaneously hypertensive rats (SHRs), Wistar-Kyoto normotensive rats (WKYs), lifetime captopril-treated SHRs, SHRs with bilateral cervical vagotomy, SHRs with bilateral sino-aortic deafferentation (SAD), and SHRs with either a single or repeated administration of naloxone methobromide (NMB). Stimulus-response functions (SRFs) were generated for neurons using 15 sec of heating of the foot at temperatures ranging from 38 to 52 degrees C. Comparisons were made of neuronal response thresholds, slopes of the SRFs, mean discharge frequency during heat stimulation, arterial blood pressure (ABP), and heart rate (HR). ⋯ However, repeated administration of NMB in SHRs resulted in a parallel, leftward shift in SRFs of both WDR and HT neurons. In all strains and treatments studied, there were no significant differences in background activities of these neurons that might contribute to the observed outcomes. In conclusion, the hypoalgesia reported in human essential hypertensives and animals with chronic hypertension may be due to a significant attenuation in spinal nociceptive transmission.(ABSTRACT TRUNCATED AT 400 WORDS)
-
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.