Vestibular testing by electrical stimulation in patients with unilateral vestibular deafferentation: galvanic evoked myogenic responses testing versus galvanic body sway testing.

Abstract

To investigate the agreement of a lesion site as indicated by two different vestibular tests with electrical stimulation, galvanic body sway testing (GBST) and galvanic evoked myogenic responses (galvanic vestibular evoked myogenic potential; galvanic VEMP) testing, in patients with unilateral vestibular deafferentation. Nineteen patients with unilateral vestibular deafferentation were studied, and the criteria for patient selection were as follows: (1) absence of a caloric response to ice water on the affected side in a supine position, and (2) absence of VEMP to 95 dBnHL clicks on the affected side. We assessed the postural response of the subjects to long duration galvanic stimulation (1 mA, 5 s) by measuring the lateral displacement at the center of foot pressure with a cathode electrode on the forehead, and an anode electrode on the mastoid (GBST). We also recorded the electromyographic (EMG) activities of the sternocleidomastoid muscle (SCM) to short duration galvanic stimulation (3 mA, 1 ms) (galvanic VEMP) with a cathode electrode on the mastoid, and an anode electrode on the forehead. In 18 of the 19 patients, the lesion site indicated by GBST was identical to that indicated by galvanic VEMP. Fourteen patients had abnormal results in both tests while 4 patients had normal results in both tests. One patient with acoustic neuroma had normal results in GBST but abnormal results in galvanic VEMP. These results suggest that electrical stimulation in these two tests stimulates the same area of the peripheral vestibular afferent system, although the duration of stimulation was different, and that the estimate of the lesion site indicated by these tests in patients with complete or nearly complete unilateral vestibular damages is reliable. These results suggest that short-duration galvanic stimulation as well as long-duration galvanic stimulation stimulates the vestibular system at the same level.