Diagnosis of sensorineural hearing loss by ipsilateral masking of brain stem auditory evoked potentials

The Authors show their original technique for the differential diagnosis of cochlear and retrocochlear hearing loss which employs ipsilateral masking of the A.B.R. in order to define the difference in V wave latency between a standard technique (clicks at 21 pps without noise) and a sensitized technique (clicks at 21 pps with noise at S/N of +40). This difference in latency has been named Sensitizing Latency Difference (SLD). Sixty normal subjects, 85 patients with cochlear hearing loss and 6 with retrocochlear hearing loss, were studied. The obtained data showed a SLD value: in normal hearing of: a) 0.31 msec. (+/- 0.14 SD) from 18 to 40 years old; b) 0.36 msec. (+/- 0.26 SD) from 41 to 60 years old; c) 0.48 msec. (+/- 0.21 SD) over 60 years old; in patients with cochlear hearing loss 0.12 msec. (+/- 0.14 SD) in 2 subjects affected by retrocochlear hearing loss a value superior to 1.5 msec. in the other 4 cases the V waves disappeared during recording of the sensitized test. A differential value of 1 msec. between cochlear and retrocochlear hearing loss was established by the Authors who with this value correctly identified all the patients with retrocochlear hearing loss and 97.8% of the subjects with cochlear hearing loss. An incorrect diagnosis of the hearing loss origin (false positives) was made in 2.2% of the patients with cochlear hearing loss. In conclusion, the Authors feel that the SLD evaluation, in consideration of its large clinical utility and of the high reliability of obtained data, is a particularly useful test in making a differential diagnosis between cochlear and retrocochlear hearing loss.