Further contributions to the genetic aspect of congenital sensorineural deafness in Dalmatians

Sensorineural deafness is a common congenital disorder in Dalmatians and is genetically transmitted. Different modes of inheritance have been proposed and the objective of this study was to study these by segregation analyses using maximum likelihood procedures. Data from 33 complete Dalmatian families were collected and data from 56 single Dalmatians added. This resulted in a total of 575 dogs with 357 known phenotypes. All dogs were clinically evaluated and electrophysiologically tested with brainstem auditory evoked responses.The prevalence of deafness was 16.5% (9.4% unilaterally deaf, 7.1% bilaterally deaf). Females were 4.4% more affected than males but this difference was not significant. Within the same litter, different phenotypic expressions of deafness occurred, which suggested different expressions of the disease. In addition, two data sets were analysed: the first included normal, uni- and bilaterally deaf dogs, the second had normal and deaf Dalmatians. We found that a recessive allele at a single biallelic major locus fitted our data best, although an incomplete penetrance of the recessive homozygotes was observed.     

Evoked otoacoustic emissions: An alternative test of auditory function in horses

Reasons for performing study: Deafness has been reported in horses due to a variety of causes and objective auditory assessment has been performed with brainstem auditory evoked potential testing. Evoked otoacoustic emission (OAE) tests are widely used in human patients for hearing screening, detecting partial hearing loss (including frequency‐specific hearing loss) and monitoring cochlear outer hair cell function over time. OAE tests are noninvasive, quick and affordable. Two types of OAE are commonly used clinically: transient evoked OAEs (TEOAEs) and distortion product OAEs (DPOAEs). Detection of OAEs has not been reported and OAE testing has not been evaluated for auditory assessment in horses. Objectives: To investigate whether TEOAEs and DPOAEs can be recorded in horses, and to evaluate the use of human OAE screening protocols in horses with apparently normal hearing. Methods: Sixteen systemically healthy horses with normal behavioural responses to sound were included. OAE testing was performed during general anaesthesia using commercially available equipment and the final outcome for each ear for the TEOAE test (after a maximum of 3 runs) and the DPOAE test (after one run) were compared. Results: TEOAEs and DPOAEs can be recorded in horses. Using the chosen TEOAE protocol, 96% of ears achieved a pass. Seventy percent of ears passed DPOAE testing, despite all of these ears passing TEOAE testing. Conclusions: Using the chosen stimulus and analysis protocols, TEOAEs were recorded from most ears; however, a smaller proportion of ears passed the DPOAE protocol, suggesting that this may be overly stringent and require further optimisation in horses. Potential relevance: OAE testing is rapid and easily performed in anaesthetised horses. It provides frequency‐specific information about outer hair cell function, and is a promising tool for audiological assessment in the horse; however, it has not been assessed in conscious or sedated animals.     

Brainstem auditory-evoked responses in horses with temporohyoid osteoarthropathy

Background: Facial and vestibulocochlear nerve dysfunction occurs commonly in horses with temporohyoid osteoarthropathy (THO); however, auditory dysfunction has not been thoroughly assessed.
Objective: To determine if auditory abnormalities occur in horses with THO.
Animals: Eleven diseased and 8 control horses.
Methods: This is a prospective study in which brainstem auditory-evoked responses (BAER) were recorded in 11 horses diagnosed with THO through neurologic, endoscopic, radiographic, or computed tomographic examinations. BAER findings were compared with those recorded from 8 adult control horses.
Results: All horses with THO were found to have BAER abnormalities that included complete unilateral BAER loss (82%, n = 9/11), partial unilateral BAER loss (18%, n = 2/11) on the most affected side, and contralateral partial BAER loss (46%, n = 5/11). Nine horses had bilateral THO based on diagnostic imaging findings; of these, 5 (56%) horses also had bilateral BAER abnormalities. The complete absence of BAER in affected horses was most consistent with peripheral sensorineural hearing loss. There was a significant association between complete BAER loss and neurologic and diagnostic abnormalities.
Conclusions and Clinical Importance: Auditory abnormalities such as complete or partial BAER loss are common in horses with THO. The BAER test is an objective diagnostic tool that can aid along with other diagnostic modalities in the assessment, management, and follow-up of horses with THO. Furthermore, BAER studies may help to elucidate the pathophysiology of THO in horses.     

Brain stem auditory potentials evoked by clicks in the presence of high-pass filtered noise in dogs

This study evaluates the effects of a high-frequency hearing loss simulated by the high-pass-noise masking method, on the click-evoked brain stem-evoked potentials (BAEP) characteristics in dogs. BAEP were obtained in response to rarefaction and condensation click stimuli from 60 dB normal hearing level (NHL, corresponding to 89 dB sound pressure level) to wave V threshold, using steps of 5 dB in eleven 58 to 80-day-old Beagle puppies. Responses were added, providing an equivalent to alternate polarity clicks, and subtracted, providing the rarefaction-condensation potential (RCDP). The procedure was repeated while constant level, high-pass filtered (HPF) noise was superposed to the click. Cut-off frequencies of the successively used filters were 8, 4, 2 and 1 kHz. For each condition, wave V and RCDP thresholds, and slope of the wave V latency-intensity curve (LIC) were collected. The intensity range at which RCDP could not be recorded (pre-RCDP range) was calculated. Compared with the no noise condition, the pre-RCDP range significantly diminished and the wave V threshold significantly increased when the superposed HPF noise reached the 4 kHz area. Wave V LIC slope became significantly steeper with the 2 kHz HPF noise. In this non-invasive model of high-frequency hearing loss, impaired hearing of frequencies from 8 kHz and above escaped detection through click BAEP study in dogs. Frequencies above 13 kHz were however not specifically addressed in this study.     

N3 potentials in response to high intensity auditory stimuli in animals with suspected cochleo-saccular deafness

We describe a previously un-reported vertex-negative potential evoked by high intensity click auditory stimuli in some dogs and cats with suspected cochleo-saccular deafness. Brainstem auditory evoked potential tracings from 24 unilaterally or bilaterally deaf animals, 22 dogs and 2 cats, among which 21 belonged to breeds with high prevalence of suspected or histologically confirmed cochleo-saccular deafness, were studied retrospectively. Values for latency, amplitude and threshold of this potential in dogs were 2.15+/-0.23 ms, 0.49+/-0.25 microV, and 91.9+/-4.7 dB NHL, respectively (mean+/-SD). Latency and threshold values in cats were in the mean+/-2 SD range of the dog values. Sensitivity to click stimulus polarity and to click stimulus delivery rate pointed towards a neural potential instead of a receptor potential. The vertex-negative wave observed in these animals shares all characteristics with the N3 potential described in some deaf humans with cochlear deafness, where it is presumed to arise from saccular stimulation. The combined degeneration of cochlea and sacculus usually reported in deaf white dogs and cats suggest that N3 may have a different origin in these species.     

Treatment of Age‐Related Hearing Loss in Dogs with the Vibrant Soundbridge Middle Ear Implant: Short‐Term Results in 3 Dogs

Background: Age‐related hearing loss (ARHL), or presbycusis, is the most common form of acquired hearing loss in dogs. Middle ear implants have been used successfully in people with ARHL who cannot benefit from conventional hearing aids. Hypothesis: Audibility improves in dogs with ARHL after implantation of the Vibrant Soundbridge (VSB) middle ear implant. Animals: Three Beagle dogs with ARHL, mean age 11.1 years. Methods: The dogs were assessed pre‐ and postoperatively by brainstem‐evoked response audiometry (BERA), otoscopy, and computed tomography scans of the ears. A VSB middle ear implant was implanted unilaterally. Three months later the functionality of the implants was assessed by auditory steady‐state responses (ASSRs), after which the dogs were euthanized for histopathological examination. Results: The VSB was implanted successfully in all dogs. Recovery from surgery was uneventful, except for transient facial nerve paralysis in 2 dogs. ASSRs showed that hearing improved after activation of the implants with a mean of 20.7, 13, and 16.3 dB at 1, 2, and 4 kHz, respectively. The implantation procedure did not affect residual hearing (with inactive implants) as measured by BERA. Conclusions and Clinical Importance: Implantation of the VSB resulted in lower ASSR thresholds, but only at the higher gain settings of the audioprocessor. As in humans, a more powerful audioprocessor is required to treat sensorineural hearing loss exceeding 20 dB in dogs. A substantial improvement in patient‐owner communication will have to be demonstrated in future studies before the procedure can be recommended in clinical practice.