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Garcia-Larrea, et al. (2002). Laser-evoked potential abnormalities in central pain patients: the influence of spontaneous and provoked pain.

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    Garcia-Larrea, et al. (2002). Laser-evoked potential abnormalities in central pain patients: the influence of spontaneous and provoked pain.

    • Garcia-Larrea L, Convers P, Magnin M, Andre-Obadia N, Peyron R, Laurent B and Mauguiere F (2002). Laser-evoked potential abnormalities in central pain patients: the influence of spontaneous and provoked pain. Brain 125:2766-81. Summary: We recorded laser-evoked cortical potentials (LEPs) in 54 consecutive patients presenting with unilateral neuropathic central pain (n = 42) or with lateralized pain of non-organic origin (n = 12). A number of cases in each group had superimposed hyperalgesia or allodynia. In patients with central pain, LEPs were significantly attenuated after stimulation over the painful territory, relative to stimulation of the homologous normal territory. LEP attenuation concerned not only patients with decreased pain/heat sensation, but also those with allodynia or hyperalgesia to laser pulses. In contrast, LEPs were never attenuated in patients with non-organic forms of pain, in whom LEPs could even be enhanced to stimulation of the painful territory. Increased responses in non-organic pain were a reminder of the cognitive modulation observed in normal subjects who direct attention to a laser stimulus. Enhanced LEPs never accompanied truly neuropathic hyperalgesia or allodynia. In central pain patients with exclusively spontaneous pain, LEP attenuation was more pronounced than that observed in those with allodynia and hyperalgesia. Patients with allodynia also presented occasionally ultra-late responses (>700 ms) to stimulation of the painful side. The hypothesis that such responses may reflect activation of a slow conducting 'medial' pain system is discussed. We conclude that, as currently recorded, LEPs essentially reflect the activity of a 'lateral' pain system subserved at the periphery by rapidly conducting A-delta fibres. They are useful to document the sensorial deficits (deafferentation) leading to neuropathic pain syndromes. Conversely, in the case of deafferentation, they fail to index adequately the affective aspects of pain sensation. On practical grounds, chronic pain coupled with reduced LEPs substantiates the diagnosis of neuropathic pain, whereas the finding of normal or enhanced LEPs to stimulation of a painful territory suggests the integrity of pain pathways, and does not support a neuropathic pathophysiology. In neuropathic cases, partial LEP preservation might increase the probability of developing provoked pain (allodynia/hyperalgesia). The possible predictive value of this phenomenon, when observed before the development of pain, remains to be demonstrated. In selected contexts (pain sine materia, non-organic anaesthesia), normal or enhanced LEPs may support a psychogenic participation in the syndrome. INSERM and Laboratoire de neurophysiologie humaine du CERMEP, Lyon, France.

    This is a very interesting article. Only those with central pain know how nice it would be to be able to document that something is wrong, whether or not that method benefits central pain.

    There are aspects of clothing in society which make our dress a strong provider of social acceptance and importance. It is so common we never really think of it. Yet, if one acquires central pain, the choice of clothing may be THE or one of THE most important aspects of life, determining whether or not one is a mental and physical exile from the rest of society. It is hard to imagine someone who cannot endure light touch, but everyone with severe Central Pain knows full well what light touch means, in terms of burning, both spontaneous and evoked.

    Paradoxically, cold is a major evoker of burning central pain, so while it would be very nice if CP subjects could wear warm clothing, they are not usually able to find anything that protects from cold blasts without causing burning from light touch from fabric. Personally, only silk seems smooth enough , and in many circumstances, not even silk is tolerable.

    If laser evoked potentials will merely identify those with central pain, we will have something concrete which the medical profession will trust. It would be nice if we didn't always have to face the trust issue. Yet, as it stands, so many with minor to moderate pains focus on them so intensely that it is difficult to separate out the person who is really in agony and anguish from central pain from those who merely react strongly to some other kind of pain. Although we are sympathetic to those with low back pain, their sheer numbers and the vague, support type treatment they receive misleads doctors into thinking Central Pain is something of the same order. NO. Central Pain is like a burn patient. It really needs active care or the patient is going to be lost in the shuffle.

    Not so long ago, medicine did not realize neuropathic pain was different from nociceptive pain. The doctor, who had never received any training in medical school for CP or even heard of it, when first faced with a case of central pain sometimes felt like he was listening to someone who claimed to have been abducted by aliens. "Independent" medical examiners (ie. those chosen by insurance companies to give biased reports in favor of the insurer) were especially harsh and many still are.

    The disease is so bizarre to the uneducated that it is entirely outside their range of experience, so they either have to take the patient totally at his word or conclude the patient is a wacko. The pain is so severe that not uncommonly the patient was at a level of desperation and neglect that he actually might have been a little wacko. Perhaps "frantic" is a beter word, but a frantic person can seem wacko if the cause is invisible. Questions arose. How could burning be caused by cold, for example. Even more bizarre, how could burning contain an element of cold, or something like it? What to make of lightning pains, pins and needles, muscle pains. It was all too much to digest. Yet, the medical profession is finally beginning to deal with it intellectually, while the patient can never actually deal with it until a cure is found.

    The only thing that caused a little pause was that it was nearly always those with spinal cord injury who complained of central pain. Why would a person who already had acceptance for their motor deficits be malingering about pain, for acceptance/ It didn't make sense, so some doctors began to take it seriously. Eventually, they realized there was a huge pain problem, bigger than the paralysis for the patient. Doctors had and have a very hard time realizing this. Rehab centers had highly trained people to work on motor deficits and no one at all to help the patient who has central pain. This is a huge gap in post SCI rehab, even today.

    Doctors always feel better if there is something concrete, so they have an orientation from which to decide whether or not the patient is sick. If Laser evoked potentials will provide this kind of footing, it can only be good for CP patients everywhere.

    Maguierre has a long history of good articles on CP. He has done a real service for us. The thing is, he actually believes it exists. This is always a help when dealing with a doctor.

    CP subjects are not whiners or malingerers. They either have to become extremely brave, or else they may well wind up as a suicide. They are actually enduring huge amounts of suffering, and their lives have been hijacked by the pain. Society is indifferent, which makes it harder when accomodations to clothing abbreviations or alterations must be made. What! You don't like my shorts in church, court, or restaurant? Well, here is my LEP report. It's for real.
    Last edited by dejerine; 2 Oct 2009, 11:25 AM.