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OBJECTIVE: To assess the clinical usefulness of an automated analysis of event-related potentials (ERPs). METHODS: Nociceptive laser-evoked potentials (LEPs) and non-nociceptive somatosensory electrically-evoked potentials (SEPs) were recorded in 37 patients with syringomyelia and 21 controls. LEP and SEP peak amplitudes and latencies were estimated using a single-trial automated approach based on time-frequency wavelet filtering and multiple linear regression, as well as a conventional approach based on visual inspection. RESULTS: The amplitudes and latencies of normal and abnormal LEP and SEP peaks were identified reliably using both approaches, with similar sensitivity and specificity. Because the automated approach provided an unbiased solution to account for average waveforms where no ERP could be identified visually, it revealed significant differences between patients and controls that were not revealed using the visual approach. CONCLUSION: The automated analysisof ERPs characterized reliably and objectively LEP and SEP waveforms in patients. SIGNIFICANCE: The automated single-trial analysis can be used to characterize normal and abnormal ERPs with a similar sensitivity and specificity as visual inspection. While this does not justify its use in a routine clinical setting, the technique could be useful to avoid observer-dependent biases in clinical research.

Neuropathic pain following peripheral nerve lesion is highly resistant to conventional pain treatments but may respond well to direct electrical peripheral nerve stimulation (PNS). In the 1980s, we treated a series of 11 peripheral neuropathic pain patients with PNS. A first outcome assessment, conducted after a 52-month follow-up, revealed that the majority of the patients were significantly improved. Here, we present the results of a second and more comprehensive follow-up, conducted after more than 20years of PNS usage. Of the six patients still using PNS, five participated in a multimodality assessment of the long-term efficacy of PNS. Home evaluations showed reduced pain ratings and improved quality-of-life during active periods of stimulation. Quantitative sensory testing confirmed the neuropathic character of the pain complaints. PNS had no significant overall effect on tactile detection, cool, warmth, cold pain and heat pain thresholds. Laser-evoked potentials showed an enlarged N2-P2 complex during active PNS. Positron Emission Tomography revealed that PNS decreased activation in the pain matrix at rest and during thermal stimulation. PNS led to increased blood flow not only in primary somatosensory cortex, but also in anterior cingulate and insular cortices, suggesting that besides activation of the dorsal column lemniscal system, other mechanisms may play a role in its analgesic effects. These data show that PNS can provide truly long-term pain relief in carefully selected patients and they provide some objective quantitative data in support of this. They encourage the planning of future prospective studies in a larger cohort of patients. ispartof: European Journal of Pain vol:15 issue:2 ispartof: location:England status: published

The assessment of the nervous system in patients with neuropathic pain is particularly challenging. Conventional electrophysiological testing, such as nerve conduction studies and somatosensory-evoked potentials, may prove normal as these techniques only evaluate large fibre function (A beta). In a clinical setting, two evaluation methods may prove useful to examine the nociceptive system or to explore small fibre function (A delta et C). First, quantitative sensory testing, derived from psychophysics, explores different sensory modalities (tactile, thermal and vibratory sensations) corresponding to different types of nerve fibres. Second, CO(2) lasers allow for powerful and selective thermal stimuli to evoke brain potentials that are specifically related to the cutaneous activation of A delta and C nociceptors. Finally, other assessments of the nervous system, such as nociceptive reflexes and microneurography, are available for use in a more experimental setting.