Dispersion of the Somatosensory Evoked Potential (SEP) in Multiple Sclerosis

A fast Fourier transform technique was used to quantitate the dispersion of the somatosensory evoked potential elicited by median nerve stimulation. The evaluation was proportional to the log of the SEP spectral energy between 380 and 1000 Hz. This was linearly scaled to a range of numbers between zero and five representing minimal mal to severe degrees of dispersion, respectively. In 21 controls, dispersion measured 1.5 ±0.6 with an upper normal limit of 2.5. In 24 MS suspects, dispersion ranged between 0.3 and 3.9. A Bayesian decision-maker, based only on spectral energy, correctly classified all of the control group and 63 percent of a patient group with definite, probable, or suspected MS. Dispersion of the SEP, when used along with other factors such as latency and shape, adds to overall diagnostic accuracy.