The current of the galvanic test is supposed to stimulate the vestibular system, but the exact location of stimulation has not been identified. Electrocochleography can determine the cochlear or retrocochlear hearing impairment due to the SP change and the threshold of AP and CM can be compared.
Patients with sensory hearing impairment and canal paresis were examined by electrocochleography (transtympanic method) and the galvanic body sway test (GBST, monopolar and monoaural method).
The following results were obtained.
1) Five of the eight patients with the cochlear type of hearing impairment showed a normal threshold of GBST (under 1mA), and all six patinets with the cochlear nerve type showed an abnormal threshold (1.1mA to 2mA) or no response with 2mA.
2) Two patients with the lesions in the brain stem, which could not be recognized N2 to N5 waves in Brain Stem Response, showed an abnormal GBST.
3) Eight patients who showed canal paresis and had diminished caloric nystagmus showed a normal GBST even when there was retrocochlear hearing impairment.
4) Eleven patients showed too marked cochlear damage CM to speculate the damage of the cochlear nerve (AP). The results of their GBST were normal in six and abnormal in five cases.
According to these results, the stimulus site of GBST is speculated to be the vestibular nerve, proximal to Scarpa's ganglion, and the sites of the lesion causing hearing impairment and canal paresis are suspected to be almost the same.