The acoustic reflex latency test: clinical application.

Acoustic reflex latency is the time interval between onset of an intense auditory stimulus and onset of middle-ear muscle contraction. The hypothesis was proposed that a retrocochlear lesion involving the afferent (VIIIth nerve) portion of the reflex arc should result in a prolongation of the reflex latency. A clinical procedure, the Acoustic Reflex Latency Test (ARLT), its protocol, methods and equipment were developed in order to test this hypothesis clinically. Absolute latency values and interaural latency differences (ILD) were established on 4 populations which included normals, cochlear lesions due to Ménière's disease, cochlear lesions of variable etiology, and 11 cases of surgically confirmed acoustic tumor. Results reveal a dramatic prolongation of latency in the presence of retrocochlear lesions (all tumors). The test was found to be most effective when 1. both ipsilateral and contralateral measurements were made, 2. stimulus frequencies of 100 Hz and 2000 Hz were employed and 3. both Absolute Latency and ILD were considered. The ARLT, while utilizing an indirect method of measurement, is a valid, cost-effective, and simple clinical procedure, yielding relative latency values and requiring only minor modifications of standard impedance equipment. The ARLT appears to have a higher efficiency rate than BERA, while providing comparable diagnostic information at a considerable saving of time, cost and personnel.