DERMATOMAL SOMATOSENSORY EVOKED POTENTIAL DEMONSTRATION OF NERVE ROOT DECOMPRESSION AFTER VAX-D THERAPY -PART V Materials And Methods : The authors theorized that the morphology of the waveforms would be distorted or suppressed prior to VAX-D therapy given that the duration of clinical symptoms ranged from 8 weeks to 60 months for the patients in this study. Treatment sessions were given Monday through Friday with patients under treatment from 2 to 7 weeks. This amount of time may have allowed nerve root functional recovery while the patient was receiving VAX-D therapy. Our study is in contrast to previous studies in the literature which eliminated patients with poorly reproducible waveforms before surgery. Intra-operative studies have focused on latency delays or a sudden loss of the first component of the waveform as a sign of acute nerve root injury. Because VAX-D therapy is a treatment which may have cumulative benefit over time , the authors assumed that as nerve roots were decompressed, electrical transmission would improve but not necessarily return the DSSEP to a truly normal waveform.We thus placed emphasis on the reconstitution of the waveform and its overall morphology, while evaluating DSSEPs generated in this study using latency and amplitude parameters consistent with the literature as well. Additionally, the literature has emphasized side to side comparisons at each nerve root level. This study compares each nerve root before and after VAX-D therapy. Several quantitative measures of waveform quality were considered, including the amplitudes of the P1-P2 and P2-P3 portions of the waveform, their post-stimulus times of occurrence, and the presence or absence of P1, P2, and P3 “peaks” (positive or negative) in the waveform. However, for some waveforms it was not possible to distinguish with certainty between true peaks and noise artifacts. In this circumstance, the authors felt that it was more practical to consider the waveform as a whole, and decide if its quality increased or decreased significantly. The quality depends on the amplitudes, the presence or absence of P1, P2, and P3 peaks, and the ability to distinguish the waveform from the noise. The measure is subjective, so all the waveforms are shown in Figure 4, and are labeled as “better”, “worse”, or “same”. These decisions were made separately by the three authors and the technician, all of whom agree with this labeling.
Posted on: Wed, 11 Sep 2013 05:37:04 +0000
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