Vestibular Electrical Evoked Potential (VEEP) Findings in Normal Controls and in Patients with Vestibular Dysfunction (P02.251)

Abstract

Objective: To report results of human VEEP studies in normal controls compared to patients with peripheral or central vestibular dysfunction. Background The VEEP has been described in animal models (cat and guinea pig) and more recently in humans. In contrast to other evoked potentials, a unique linear relationship between current strength and latency has been reported with VEEP responses in normal individuals. Design/Methods: Normal control subjects (n=5) and patients with vestibular dysfunction (n=3) were studied with electrical stimulation over the mastoid in one mA increments from threshold to no higher than 20 mA. Evoked potentials were recorded with standard signal averaging techniques. Results: In normal controls, mastoid stimulation at 2.5mA yielded Cz-A1/2 VEEP responses of median latency 10.2ms (range 6.0-13.3; SD 4.9). These responses progressively increased in latency from 8.6 to 22.6ms (mean latency increase of 1.3ms/mA) as current strength was increased in 10 steps (1mA/step) from threshold. VEEP responses differed significantly in stimulation threshold, morphology, amplitude and latency from mastoid dermatomal somatosensory evoked potentials (SEPs), great auricular sensory nerve action potentials (SNAPs), and frontalis compound muscle action potentials (CMAPs). Neither acoustic stimuli nor white noise masking affected the VEEP. In 3 patients with vestibular dysfunction (one each with acoustic neuroma, Meniere disease and multiple sclerosis as the cause) VEEP late response latencies were absent or markedly asymmetric, with recordable responses showing a median latency of 12.2ms (range 11.2-12.7; SD 0.4); none demonstrated the linear increasing current strength-latency pattern seen in normals. Conclusions: 1) VEEP studies produced reproducible responses in normal controls; 2) VEEP responses cannot be attributed to auditory or somatic sensory nerve responses; 3) VEEP current strength-latency curves showed a linear increase in normals in contrast to absent, flat, and/or decreasing patterns in patients with vestibular dysfunction. Supported by: Mayo Foundation. Disclosure: Dr. Smith has nothing to disclose. Dr. Cevette has nothing to disclose. Dr. Stepanek has nothing to disclose. Dr. Cocco has nothing to disclose. Dr. Pradhan has nothing to disclose. Dr. Brookler has nothing to disclose. Dr. Zapala has nothing to disclose. Dr. Ross has nothing to disclose.