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Future ambulation prognosis as predicted by somatosensory evoked potentials in motor complete and incomplete
S R Jacobs1, N K Yeaney, G J Herbison
1Department of Rehabilitation Medicine Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA, USA.
Objective:
The purpose of this prospective study was to determine the efficacy of tibial somatosensory evoked potentials (SEPs) in predicting ambulation in tetraplegic individuals.
Design:
This was a prospective study of a cohort of cervical spinal cord-injured patients who had SEPs recorded within 72 hours to 2 weeks post-SCI and whose ambulation outcome was followed up to 2 years post-SCI.
Setting:
Regional Spinal Cord Injury (SCI) Center.
Patients:
All male and female subjects admitted to the center from 1988 to 1991 between the ages of 15 and 60 years who demonstrated C4 through T1 complete and incomplete acute SCIs were asked to participate in this study.
Measurements:
The tibial nerve cortical SEPs were graded as either present or absent. The waveforms were also graded as less than 0.5 microV or > or = 0.5 microV. Quadriceps strength plus touch and pin sensation were tested within 72 hours to 2 weeks post-SCI. Ambulation was rated as absent, exercise, household, or community. The ambulatory and clinical status were assessed monthly for 3 months, and then at 6, 12, 18, and 24 months post-SCI. Statistical analysis using the two-tailed Fisher's exact test was performed relating the initial clinical and SEP data to ambulation outcome up to 24 months post-SCI.
Results:
All 13 subjects with a right and/or left quadriceps manual muscle test (MMT) greater than 0/5 became ambulatory. Of the 9 subjects with an initial bilateral quadriceps MMT = 0/5, only 1 recovered enough lower limb function to ambulate (p = .0001). One of the 7 subjects with absent touch sensation in the lower limbs became ambulatory, whereas 14 of the 15 subjects with touch sensation present became ambulatory (p = .002). All 7 subjects with absent pin sensation in the lower limbs were nonambulatory, and 14 of 15 subjects with pin sensation present became ambulatory (p < .0001). Of the 9 subjects with bilaterally absent cortical SEP waveforms, 2 became ambulatory. Twelve of the 13 subjects with a cortical SEP wave present became ambulatory (p = .0015). Of the 10 subjects with a cortical SEP wave amplitude less than 0.5 microV, only two became ambulatory, whereas all 12 subjects with an amplitude > or = 0.5 microV became ambulatory (p = .00014). In no subject did the SEP predict future ambulation where the clinical examination did not also predict recovery of ambulation.
Conclusion:
Both the early postinjury clinical evaluation and the SEP predicted ambulation outcome to a significant degree, but the SEP offered no additional prognostic accuracy over that provided by the clinical examination.