Sensitivity of laser-evoked potentials versus somatosensory evoked potentials in patients with multiple sclerosis.
OBJECTIVE
Somatosensory evoked potentials (SEPs) play a less important role in the diagnosis of multiple sclerosis (MS) than visually evoked potentials. Since standard SEPs only reflect the dorsal column function, we now investigated spinothalamic tract function in patients with MS using laser-evoked potentials (LEPs).


METHODS
LEPs to thulium laser stimuli (3ms, 540 mJ, 5mm diameter) were recorded from 3 midline positions (Fz, Cz, Pz) in 20 patients with MS, and 6 patients with possible but unconfirmed MS. Peak latencies and peak-to-peak amplitude of the vertex potential negativity (N2) and positivity (P2) were evaluated and compared with normative values from 22 healthy control subjects. Median and tibial nerve SEPs were recorded with standard methods. Depending on the results of sensory testing, two skin areas (both hands, both feet, or one hand and foot of the same body side) were assessed in each patient.


RESULTS
In group comparisons, LEPs in patients with MS were significantly delayed and reduced in amplitude compared with healthy subjects (P<0.001) or patients with suspected but unconfirmed MS (P<0.05). In intraindividual comparisons within the patients with MS, LEP amplitude was significantly lower (P<0.01) and latencies were significantly longer (N2: P<0.01; P2: P<0.05) for a clinically hypoalgesic skin area than an unaffected control area. On a single case basis, LEPs were abnormal in 12 (60%) and SEPs in 8 (40%) of the patients with MS; combined analysis of LEPs and SEPs raised sensitivity to 75% (15 patients). LEPs were also abnormal for 7 skin areas with clinically normal nociception and thermal sensitivity, indicating subclinical lesions. Standard SEPs detected subclinical lesions in 5 areas with normal tactile sensitivity.


CONCLUSIONS
In patients with multiple sclerosis, spinothalamic tract function and LEPs were impaired more often than dorsal column function and SEPs. LEPs also detected subclinical lesions. Combined assessment of LEPs and SEPs can help to document dissemination of demyelinating CNS lesions and thus contribute to the diagnosis of multiple sclerosis.
Spiegel
Jörg
J
Institute of Physiology and Pathophysiology, Johannes Gutenberg-University, Saarstrasse 21, D-55099, Mainz, Germany.
Hansen
Christiane
C
Baumgärtner
Ulf
U
Hopf
Hanns Christian
HC
Treede
Rolf Detlef
RD
D000328:Adult; D000893:Anti-Inflammatory Agents; D016022:Case-Control Studies; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006225:Hand / Q000503:physiopathology; D006801:Humans; D006854:Hydrocortisone / Q000627:therapeutic use; D007074:Immunoglobulin G / Q000378:metabolism; D007259:Infrared Rays; D007834:Lasers; D007866:Leg / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D011930:Reaction Time; D015203:Reproducibility of Results; D012684:Sensory Thresholds; D013133:Spinothalamic Tracts / Q000503:physiopathology*
D000893:Anti-Inflammatory Agents; D007074:Immunoglobulin G; D006854:Hydrocortisone