Article
Laser-evoked potentials: a diagnostic approach to the dorsal root
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Published: | June 13, 2005 |
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Outline
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Introduction
The functional diagnostic of the dorsal root is especially effective via nociceptive fibers on account of less intersegmental overlap compared to large diameter fibers of the mechanoreceptive afferents. Laser evoked potentials (LEP) are induced by short, painful heat stimuli. Aim of this work was to document interside differences of dermatomal LEP in healthy subjects and to describe changes of the LEP in patients with acute monosegmental dorsal root affection.
Materials and Methods
Dorsal root function was tested in 12 healthy subjects and 40 patients suffering from acute radiculopathy (one of the segments L4 to S1). Mechanosensibility and thermosensibility were clinically investigated. LEP were induced by slightly painful stimuli (80 on the affected and 80 on the contralateral unaffected dermatome). The LEP were evaluated by amplitude of the averaged electroencephalogram (eeg). In addition a subjective pain rating was recorded after each stimulus.
Results
Norm data revealed normal interside latency differences of ±16 % for the N-component and ±13 % for the P-component and normal interside amplitude differences of ±30%. Over all 22 patients showed pathological LEP-changes (amplitude decrease 30-50%: 7 patients, >50%: 8 patients, loss of LEP 3 patients, latency changes: 9 patients).
Discussion
In patients with acute radiculopathy LEP changes allow a graduation of loss of dorsal root function. It is discussed what mechanisms are responsible as concerns deafferentiation and neuropathy of the dorsal root fibers. We assume that LEP changes have prognostic relevance in patients with dorsal root affection.