A 3-month-old, intact male French bulldog was suspected of deafness. The dog was irresponsive to environmental noises generated out of sight, but normal responses were noted for visual stimuli. No abnormalities were observed on the neurological, otoscopic, radiographic, and blood examinations. To diagnose the apparent deafness, brainstem auditory evoked potential (BAEP) was recorded in the presented dog together with a normal dog. While the BAEP from the control dog showed a normal wave consisting of 5 peaks, absence of all peaks was noted in the suspected deaf dog. Therefore the dog was definitively diagnosed as bilaterally congenital sensorineural deafness.

The objective of this study was to evaluate any otopathologic changes in temporal bone specimens from dogs with deafness related to cochleosaccular (Scheibe) dysplasia (CSD). We used the canine temporal bone collections of the Otopathology Laboratory at the University of Minnesota and of the Massachusetts Eye and Ear Infirmary at Harvard University in Boston. Our morphometric analysis included measuring the areas of the stria vascularis and the spiral ligament and counting the number of spiral ganglion cells. In addition, we noted the presence of the organ of Corti and cochlear hair cells, assessed the location of Reissner's membrane and the saccular membrane, and counted the number of both Type I and Type II vestibular hair cells in the macule of the saccule and vestibular ganglion cells. In the group of specimens from dogs with cochleosaccular dysplasia, we observed generalized degeneration in the cochlea and a significantly decreased number of Type I and Type II vestibular hair cells and vestibular ganglion cells. As hereditary deafness is presently untreatable with known therapeutic methods, dogs with cochleosaccular dysplasia should not be considered for breeding. Future therapeutic approaches, such as stem cell therapies, should be designed to target all the elements of the cochlea in addition to the saccule as it was found that both are affected in dogs with CSD.

Bilateral deafness with concurrent vestibular dysfunction was first reported in the Doberman pinscher in 1980. Here, we identify a coding mutation in the MYO7A gene that is perfectly associated with the disorder. The lack of visual deficits in affected dogs suggests that, like rodents but unlike humans, MYO7A is not required for retinal function. DNA testing of the mutation will enable dog breeders to manage the incidence of this genetic defect.

Brain stem auditory evoked potential (BAEP) testing with air-conducted click stimuli can be used to diagnose sensorineural deafness in dogs if conductive deafness can be ruled out. Detection of conductive deafness can be performed by recording BAEP elicited by a vibratory stimulus transducer placed against the skull. Air- and bone-conducted BAEP were compared in dogs, varying bone stimulator placement, click polarity, and stimulus intensity. Optimal bone stimulator placement was determined to be over the mastoid process, followed by the mandible and the zygomatic arch. Condensation polarity clicks gave responses preferable to those elicited by rarefaction or alternating polarity. Bone-conducted BAEP peak latencies were significantly longer than air-conducted latencies after correction of the latencies for the air conduction time accompanying air-conducted stimuli. Significant differences between stimulus modalities were not seen for BAEP peak amplitudes or interpeak latencies. Latency-intensity and amplitude-intensity regressions had similar effects for both modalities: latencies decreased and amplitudes increased as stimulus intensity increased.