P1-latency interroot comparison enhances the validity of scalp-recorded somatosensory-evoked potentials to diagnose nerve root dysfunction in sciatica.
METHODS
A prospective validity study was done of scalp-recorded somatosensory-evoked potentials as a diagnostic procedure to show lumbosacral radiculopathy in 100 consecutive patients with unilateral or bilateral sciatica.


OBJECTIVE
To determine the validity gained by the use of P1-latency interroot comparison to show P1-latency prolongation.


BACKGROUND
The validity of scalp-recorded somatosensory-evoked potentials in diagnosing lumbosacral radiculopathy has been debated and is uncertain.


METHODS
Sensory nerves representing nerve roots L4, L5, and S1 were stimulated bilaterally. Height-corrected P1-latency, two new P1-interroot comparison-based criteria, and absence of P1 were studied. The gold standard was defined as clinically-involved nerve roots with radiologic nerve root compression. The false-positive nerve root compression rate was determined, and the gold standard was corrected accordingly. Clinically relevant cut-off values were defined by multilevel likelihood ratio analysis.


RESULTS
The positive and negative likelihood ratios of P1-latency prolongation were 6.79 and 0.53, respectively, for the gold standard, and 10.57 and 0.21, respectively, for the corrected gold standard. The validity was not reduced when scalp-recorded, somatosensory-evoked potentials were blinded to the radiologic results. Absence of P1 was associated to the gold standard and the corrected gold standard. Compared with the combined use of P1-latency interside difference and height-corrected latency, the combination of P1-interroot comparison and height-corrected P1-latency increased the sensitivity by 20% for the gold standard and 32% for the corrected gold standard, and when absent P1 was added, the overall sensitivity was 53% for the gold standard and 81% for the corrected gold standard. The corresponding specificity was 92%, and in asymptomatic nerve roots it was 98%.


CONCLUSIONS
The P1-interroot comparison permits the use of scalp-recorded somatosensory-evoked potentials as a contributory "rule in" procedure in patients with sciatica.
Pape
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Department of Neurology, Ullevål City Hospital, University of Oslo, Norway.
Eldevik
O P
OP
D000293:Adolescent; D000328:Adult; D000368:Aged; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008161:Lumbosacral Region / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D009192:Myelography / Q000592:standards; D009408:Nerve Compression Syndromes / Q000000981:diagnostic imaging / Q000503:physiopathology; D011129:Polyradiculoneuropathy / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D011446:Prospective Studies; D012015:Reference Standards; D015203:Reproducibility of Results; D012535:Scalp; D012585:Sciatica / Q000000981:diagnostic imaging* / Q000503:physiopathology*