Correlation analysis of somatosensory evoked potential waveforms: clinical applications.

OBJECTIVE: To assess the validity of the correlation coefficient (CC) as a diagnostic tool in evaluating somatosensory evoked potential (SEP) waveforms. DESIGN: SEP waveforms were recorded over the spine and scalp in response to tibial nerve stimulation at the ankle for 30 patients. SETTING: A general community, ambulatory, private referral center. PATIENTS: Patients were all ambulatory and were selected randomly from among existing patient records at the medical center. MAIN OUTCOME MEASURE: The test for validity uses the CC to verify reproducibility. The test for side-to-side symmetry uses the CC to obtain a measure of similarity between left and right tibial scalp responses. For both tests, a table is presented with CCs for normal subjects. If the CC for each patient falls below the appropriate critical value from the table, then the CC is taken to be abnormal; p values are provided at specific levels in this table. RESULTS: A new data base for the means and critical values of CCs with corresponding p values is established for normal subjects. Most of the patient data reveal significant CC nonreproducibility and lack of symmetry in tibial scalp SEP waveforms. CONCLUSION: The CC provides objective and quantitative waveform information that complements latency and amplitude measurements in the clinical interpretation of tibial scalp SEP waveforms.

Correlation analysis of somatosensory evoked potential waveforms.

Somatosensory evoked potential (SEP) waveforms were recorded over the spine and scalp in response to tibial nerve stimulation at the ankle for 28 subjects. The scalp data were analyzed with the correlation coefficient (CC) to determine the reproducibility of the signals and to identify side-to-side symmetry. The test for reproducibility uses the CC to verify validity, a low CC implying that the data are defective. The symmetry test uses the CC to obtain a measure of similarity of the responses to stimulation from opposite sides of the body. Statistics are presented showing the normal ranges of the CC values and their standard deviations. We conclude that the CC can provide objective and quantitative waveform information that complements latency and amplitude measurements in the clinical interpretation of tibial SEP waveforms.