Question
I have some questions about interpretation of the VEMP. - Do you determine normal/abnormal results from latency or amplitude of P13 and N23?
- If latency is the determinant, what latency delay is significant?
- I understand that to calculate results, you use amplitude. Does that refer to peak to peak amplitude (P13 to N23)?
- What management/rehabilitation suggestions do you provide patients with an abnormal VEMP?
Answer
The clinical interpretation of the VEMP has focused primarily on P1/N1 (P13/N23) amplitude measurements or threshold asymmetries between the right and left sides, although there are a few reports of prolonged P1 (P13) latencies in patients with central pathologies. Side-to-side differences in VEMP amplitude (A) are often expressed as an asymmetry ratio calculated as:
Asymmetry Ratio = 100 |(AL - AR)/(AL + AR)|where AL equals the peak-to-peak amplitude (P1/N1) on the left side and AR equals the peak-to-peak amplitude on the right side.
VEMP abnormalities vary with vestibular pathology. Abnormally increased amplitude and reduced thresholds have been reported in patients with superior canal dehiscence. In contrast, reduced amplitude or absent VEMPs have been reported in some patients with vestibular schwannoma, Meniere's disease, acoustic neuroma, and herpes zoster oticus. An attenuated or absent VEMP suggests saccular and/or inferior nerve involvement. Patients with reduced amplitude VEMPs may be candidates for vestibular rehabilitation therapy (VRT), however, the efficacy of VRT for patients with otolithic disturbances has not been determined.
Faith Akin, Ph.D. is the Director of the Vestibular/Balance Laboratory at the James H. Quillen VA Medical Center, Mountain Home TN and Assistant Professor, Departments of Communicative Disorders and Surgery, East Tennessee State University, Johnson City, TN. Her research has focused on the clinical assessment of vestibular function. She has been a funded investigator through the Rehabilitation Research and Development Service of the Veterans Health Administration for the past six years.
