Original article
Clinical usefulness of laser-evoked potentials

https://doi.org/10.1016/j.neucli.2003.10.009Get rights and content

Abstract

In contrast to the function of the visual or auditory pathways which are electrophysiologically accessible by visual or auditory evoked potentials, the somatosensory pathway cannot be investigated as a whole by conventional somatosensory evoked potentials (SEP), because these only reflect function of large fibers, dorsal columns, medial lemniscus and their thalamo-cortical projections mediating sensations like touch and vibration. The other half of the somatosensory system, signaling temperature and pain perception, uses a different set of afferents and different central pathways, the function of which is accessible by laser-evoked potentials (LEPs). LEP can document lesions of the spinothalamic tract and (lateral) brainstem and of thalamo-cortical projections conveying thermo-nociceptive signals. In the peripheral nerve, LEP can help distinguish between large and small fiber neuropathies. The rapid heating of the skin by infrared laser pulses can easily be applied to non-glabrous skin in any dermatome. In recent years, many clinical studies have demonstrated that LEP can supply evidence for establishing clinical diagnoses when deficits of the nociceptive system are present. This review outlines principles and recording techniques for LEP in patients and compiles typical LEP findings in patients with lesions due to different diseases at various levels of the nociceptive pathways. Limitations for the use of LEP are pointed out, too, like the uncertainty of lesion location along these pathways and the fact that LEP can reliably show correlates of reduced nociceptive function but only rarely of enhanced transmission (like in hyperalgesia).

Résumé

Contrairement aux fonctions visuelles ou auditives, facilement accessibles sur le plan électrophysiologique via les potentiels évoqués correspondants, les voies somesthésiques ne peuvent pas être explorées complètement avec les potentiels évoqués somesthésiques (PES), car ceux-ci ne reflètent que la fonction des fibres de plus gros calibre, les cordons postérieurs, le lemniscus médian et les projections thalamo-corticales sous-tendant des sensations comme le toucher et la vibration. L'autre moitié du système somesthésique, qui a la charge de signaler les sensations de douleur et de température, utilise des groupes différents de fibres afférentes dans la périphérie et des projections différentes au niveau central, dont la fonction est accessible par les potentiels évoqués par pulsation laser (PEL). Les PEL détectent les lésions du système spinothalamique dans la moelle et le tronc cérébral latéral, ainsi que celles des projections thalamo-corticales conduisant les signaux thermo-nociceptifs. Dans le système périphérique, les PEL aident à distinguer les neuropathies concernant les fibres de gros ou de petit calibre. La stimulation laser entraîne un réchauffement cutané très rapide, qui peut être appliqué à la peau poilue sur pratiquement tous les dermatomes. Des nombreuses études cliniques ont montré l'importance des PEL comme aide au diagnostique clinique en cas de déficit patent ou suspecté du système nociceptif. Cette revue s'intéresse d'abord aux principes et techniques de l'enregistrement des PEL chez le patient, et compile des résultats typiques chez des patients porteurs de lésions à différents niveaux des voies thermo-nociceptives. Nous signalons également certaines limites de ce type d'examen, comme les incertitudes quant à la localisation topographique des lésions détectées, ainsi que le fait que les PEL montrent de façon fiable des signes de diminution des fonctions nociceptives, mais témoignent rarement des augmentations de la transmission douloureuse (comme l'hyperalgesie).

Section snippets

General considerations

The visual and auditory pathways are projecting one modality only, and can thus be easily tested using visual and auditory evoked potentials (VEP, AEP). Pain pathways are a part of the somatosensory system. Therefore, neurophysiological studies of pain pathways may be expected to be related to the recording of somatosensory evoked potentials (SEP). However, the somatosensory system includes more than one modality and cannot electrophysiologically be tested by only one type of evoked potential.

Stimulation

In normal skin, the sensation evoked by laser stimuli near pain threshold is comparable to a weak pinprick or pulling a single hair follicle. In order to obtain reproducible evoked potentials, it is necessary to use suprathreshold stimuli, which are usually perceived as slightly stinging and/or burning [13], [57], and are less uncomfortable than the standard electrical nerve stimuli used for SEP recording. Within the range of 7–50 ms stimulus duration and 3–9 mm beam diameter, pain threshold is

Pathological LEP changes

The anatomical specificity of the peripheral and central thermoreceptive and nociceptive pathways represents the major rationale of a clinical use of the LEP method. Many groups documented disturbances of pain and temperature sensitivity by abnormal LEP that are typically missed by the standard SEP method in a variety of pathologies (Table 2). Evidence strongly indicates, and will be reviewed below, that LEP usefully supplement standard electrical SEP when minus-signs of the pain and

Topodiagnosis of lesions using LEP

As shown in the previous section, LEP can document lesions anywhere along the nociceptive pathway (Fig. 3). Although all dermatomes are accessible, the absence of an LEP in a patient cannot necessarily provide the exact level of the lesion without additional clinical, electrophysiological or imaging data. The absence of an LEP may be due to a lesion anywhere between the cortex and the dermatomal level of the spinal cord where the stimulation is done, or even in the periphery. It is important to

Conclusions

Standard SEP are of limited value in patients, who present with a dissociated sensory loss of pain and temperature sensitivity and preserved tactile and proprioceptive sensitivity. The technique of LEP recording allows the assessment of the functional status of the nociceptive pathways within the somatosensory system. According to the anatomy of the nociceptive pathways, this type of a sensory deficit occurs predominantly with peripheral, spinal, or brainstem lesions. LEP abnormalities consist

Acknowledgments

Supported by the Deutsche Forschungsgemeinschaft (Tr 236/13-2) and NIH (NS 38493).

References (92)

  • M. De Tommaso et al.

    Heat pain thresholds and cerebral event-related potentials following painful CO2 laser stimulation in chronic tension-type headache

    Pain

    (2003)
  • D. Devos et al.

    Normative values for upper and lower limbs

    Neurophysiol Clin

    (2000)
  • S.J. Gibson et al.

    Altered heat pain thresholds and cerebral event-related potentials following painful CO2 laser stimulation in subjects with fibromyalgia syndrome

    Pain

    (1994)
  • M. Granot et al.

    Simultaneous recording of late and ultra-late pain evoked potentials in fibromyalgia

    Clin Neurophysiol

    (2001)
  • J.D. Greenspan et al.

    Pain sensitivity alterations as a function of lesion location in the parasylvian cortex

    Pain

    (1999)
  • R. Kakigi et al.

    Physiological study of the spinothalamic tract conduction in multiple sclerosis

    J Neurol Sci

    (1992)
  • R. Kakigi et al.

    Physiological functions of the ascending spinal tracts in HTLV-I-associated myelopathy (HAM)

    Electroenceph Clin Neurophysiol

    (1992)
  • R. Kakigi et al.

    Pain-related somatosensory evoked potentials following CO2 laser stimulation in man

    Clin Neurophysiol

    (1989)
  • M. Kanda et al.

    Pain-related and cognitive components of somatosensory evoked potentials following CO2 laser stimulation

    Electroenceph Clin Neurophysiol

    (1996)
  • P. Kropp et al.

    Prediction of migraine attacks using a slow cortical potential, the contingent negative variation

    Neurosci Lett

    (1998)
  • V. Kunde et al.

    Topography of middle-latency somatosensory evoked potentials following painful laser stimuli and non-painful electrical stimuli

    Electroenceph Clin Neurophysiol

    (1993)
  • V. Legrain et al.

    Nociceptive processing in the human brain of infrequent task-relevant and task-irrelevant noxious stimuli. A study with event-related potentials evoked by CO2 laser radiant heat stimuli

    Pain

    (2003)
  • J. Lorenz et al.

    Middle and long latency somatosensory evoked potentials after painful laser stimulation in patients with fibromyalgia syndrome

    Electroenceph Clin Neurophysiol

    (1996)
  • W. Magerl et al.

    C- and A-fiber components of heat-evoked cerebral potentials in healthy human subjects

    Pain

    (1999)
  • A. Ragazzoni et al.

    Electric and CO2 laser SEPs in a patient with asymptomatic syringomyelia

    Electroenceph Clin Neurophysiol

    (1993)
  • A. Romaniello et al.

    Assessment of nociceptive trigeminal pathways by laser-evoked potentials and laser silent periods in patients with painful temporomandibular disorders

    Pain

    (2003)
  • R. Siedenberg et al.

    Laser-evoked potentials: exogenous and endogenous components

    Electroenceph Clin Neurophysiol

    (1996)
  • J. Spiegel et al.

    Sensitivity of laser-evoked potentials versus somatosensory evoked potentials in patients with multiple sclerosis

    Clin Neurophysiol

    (2003)
  • J. Spiegel et al.

    Clinical evaluation criteria for the assessment of impaired pain sensitivity by thulium-laser evoked potentials

    Clin Neurophysiol

    (2000)
  • A.D. Towell et al.

    Sensory and cognitive components of the CO2 laser evoked cerebral potential

    Electroenceph Clin Neurophysiol

    (1993)
  • R.-D. Treede et al.

    Dissociated secondary hyperalgesia in a subject with a large-fibre sensory neuropathy

    Pain

    (1993)
  • R.-D. Treede et al.

    Late somatosensory evoked cerebral potentials in response to cutaneous heat stimuli

    Electroenceph Clin Neurophysiol

    (1988)
  • R.-D. Treede et al.

    Laser-evoked potentials for assessment of nociceptive pathways in humans. Toward a rational experimental and clinical use

    Pain Forum

    (1998)
  • A. Truini et al.

    Laser-evoked potentials in post-herpetic neuralgia

    Clin Neurophysiol

    (2003)
  • M. Valeriani et al.

    Short-term plastic changes of the human nociceptive system following acute pain induced by capsaicin

    Clin Neurophysiol

    (2003)
  • M. Valeriani et al.

    Reduced habituation to experimental pain in migraine patients: a CO2 laser evoked potential study

    Pain

    (2003)
  • T. Weiss et al.

    The influence of semantic priming on event-related potentials to painful laser-heat stimuli in migraine patients

    Neurosci Lett

    (2003)
  • Q. Wu et al.

    Hyperalgesia with reduced laser evoked potentials in neuropathic pain

    Pain

    (1999)
  • M. Yamamoto et al.

    Pain-related somatosensory evoked potentials in dementia

    J Neurol Sci

    (1996)
  • R. Zaslansky et al.

    The P300 in pain evoked potentials

    Pain

    (1996)
  • G. Antonini et al.

    Sensory involvement in spinal-bulbar muscular atrophy (Kennedy's disease)

    Muscle Nerve

    (2000)
  • L. Arendt-Nielsen et al.

    Involvement of thin afferents in carpal tunnel syndrome: evaluated quantitatively by argon laser stimulation

    Muscle Nerve

    (1991)
  • R. Baron et al.

    Postherpetic neuralgia. Are C-nociceptors involved in signalling and maintenance of tactile allodynia?

    Brain

    (1993)
  • U. Baumgärtner et al.

    Laser-evoked potentials in the assessment of pain in BPD. XII

  • A. Beydoun et al.

    Laser evoked potentials: correlation with pain and temperature deficits due to stroke

    Neurology

    (1994)
  • R. Biehl et al.

    Pain ratings of short radiant heat pulses

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