How are caloric stimulation electronystagmography (ENG) results interpreted?

Updated: Aug 06, 2019
  • Author: Angela G Shoup, PhD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Answer

In the normal vestibular system, adequate, equivalent responses should be obtained from each ear. A normal caloric response does not rule out a vestibular pathology, however, since this test only measures a response from part of the labyrinth at a very low frequency of stimulation.

Slow phase velocity is determined for each recording for use in the following calculations.

Unilateral weakness (UW) is used to evaluate symmetry, as calculated by the following equation:

%UW = [((RC + RW) – (LC + LW))/(RC + RW + LC + LW)] × 100

A negative number indicates a right unilateral weakness, and a positive number indicates a left unilateral weakness. Unilateral weakness is indicative of a peripheral vestibular lesion that involves the nerve or end-organ on the side of the weakness. In many clinics, a UW greater than 25% is significant.

Average caloric responses of 6 degrees per second or less are consistent with a bilateral weakness. Borderline bilateral weakness is noted when the average responses are between 7-9 degrees per second. Abnormally weak bilateral responses may be due to bilateral peripheral vestibular pathology or central interruption of the vestibuloocular reflex. When a borderline bilateral weakness or bilateral weakness is observed, drug effects should be excluded.

If the patient has spontaneous nystagmus, directional preponderance (DP) is evident, as calculated by the following equation:

%DP = [((LC + RW) – (RC + LW))/(RC + RW + LC + LW)] × 100

In general, a directional preponderance greater than 20-30% is considered significant.


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