Brain stem auditory-evoked response abnormalities in 14 dogs with confirmed central nervous system lesions

Rapid hearing threshold assessment with modified auditory brainstem response protocols in dogs

Introduction

Auditory brainstem response (ABR) is the gold standard for hearing testing in dogs. ABR is commonly used in puppies to diagnose congenital sensorineural deafness. Long test times limit the use for a more comprehensive hearing screening in veterinary practice. This study aimed to establish a super-fast hearing screening protocol in dogs.

Methods

Hearing thresholds were routinely measured with a mobile device designed for newborn hearing screening in 90 dogs. We introduced modifications of the ABR protocol, e. g., a binaural test mode, higher stimulus rates, a broadband chirp stimulus, and an algorithm for automatic peak V detection in a stepwise fashion. Hearing thresholds were then measured with fast protocols utilizing either 30 Hz click or 90 Hz broadband chirp stimuli with 80, 60, 40, 30, 20, 10, 0 and -10 dBnHL stimulation intensities. Interrater reliability, agreement between click and chirp hearing thresholds and correlations with clinical characteristics of the dogs were assessed.

Results

Using all innovations, the test time for hearing threshold assessment in both ears was reduced to 1.11 min (mean). The chirp stimulus accentuated both, peak V and the subsequent trough, which are essential features for judgement of the hearing threshold, but preceding peaks were less conspicuous. Interrater reliability and agreement between click and chirp hearing threshold was excellent. Dogs >10 years of age and dogs with abnormal hearing score or otitis score had significantly higher hearing thresholds than younger dogs (p ≤ 0.001) or dogs without abnormalities (p < 0.001).

Conclusion

The results demonstrate that modifications in ABR protocols speed-up test times significantly while the quality of the recordings for hearing threshold assessment is maintained. Modified ABR protocols enable super-fast hearing threshold assessment in veterinary practice.

Clinical presentation, diagnosis, treatment, and outcome in 8 dogs and 2 cats with global hypoxic-ischemic brain injury (2010-2022)

BACKGROUND

Global hypoxic-ischemic brain injury (GHIBI) results in variable degrees of neurological dysfunction. Limited data exists to guide prognostication on likelihood of functional recovery.

HYPOTHESIS

Prolonged duration of hypoxic-ischemic insult and absence of neurological improvement in the first 72 hours are negative prognostic indicators.

ANIMALS

Ten clinical cases with GHIBI.

METHODS

Retrospective case series describing 8 dogs and 2 cats with GHIBI, including clinical signs, treatment, and outcome.

RESULTS

Six dogs and 2 cats experienced cardiopulmonary arrest or anesthetic complication in a veterinary hospital and were promptly resuscitated. Seven showed progressive neurological improvement within 72 hours of the hypoxic-ischemic insult. Four fully recovered and 3 had residual neurological deficits. One dog presented comatose after resuscitation at the primary care practice. Magnetic resonance imaging confirmed diffuse cerebral cortical swelling and severe brainstem compression and the dog was euthanized. Two dogs suffered out-of-hospital cardiopulmonary arrest, secondary to a road traffic accident in 1 and laryngeal obstruction in the other. The first dog was euthanized after MRI that identified diffuse cerebral cortical swelling with severe brainstem compression. In the other dog, spontaneous circulation was recovered after 22 minutes of cardiopulmonary resuscitation. However, the dog remained blind, disorientated, and ambulatory tetraparetic with vestibular ataxia and was euthanized 58 days after presentation. Histopathological examination of the brain confirmed severe diffuse cerebral and cerebellar cortical necrosis.

CONCLUSIONS AND CLINICAL IMPORTANCE

Duration of hypoxic-ischemic insult, diffuse brainstem involvement, MRI features, and rate of neurological recovery could provide indications of the likelihood of functional recovery after GHIBI.

Cytological and microbiological characteristics of middle ear effusions in brachycephalic dogs

Background

Middle ear effusion is common in brachycephalic dogs with similarities to otitis media with effusion in children. Association with the cranial and eustachian tube morphology and bacterial infection is suspected in both species.

Hypothesis/objectives

To determine cytological and bacteriological features of middle ear effusions in dogs, provide information on histological features, and further assess the dog as a model of the human disease.

Animals

Sixteen live dogs, 3 postmortem cases of middle ear effusion, and 2 postmortem controls.

Methods

Prospective; clinical investigation using computed tomography, magnetic resonance imaging, video‐otoscopy, myringotomy; cytological assessment of 30 and bacteriology of 28 effusions; histology and immunohistochemistry (CD3 for T‐lymphocytes, Pax5 for B lymphocytes and MAC387 for macrophages) of 10 middle ear sections.

Results

Effusions were associated with neurological deficits in 6/16 (38%) and concurrent atopic dermatitis and otitis externa in 9/16 (56%) of live cases. Neutrophils and macrophages predominated on cytology (median 60 [range 2%‐95.5%] and 27 [2%‐96.5%]) whether culture of effusions was positive or not. In histology sections, the mucosa was thickened in affected dogs but submucosal gland dilatation occurred in affected and unaffected dogs. There was no bacterial growth from 22/28 (79%) of effusions. Bacteria isolated from the other 6 (21%) were predominantly Staphylococcus pseudintermedius (4/6, 67%).

Conclusions and Clinical Importance

Clinical, morphological, and cytological findings in middle ear effusions of dogs and people suggest similar pathogeneses. Middle ear effusion of dogs could be a useful model of human otitis media with effusion. Such comparisons can improve understanding and management across species.

Evaluation of central vestibular syndrome in dogs using brainstem auditory evoked responses recorded with surface electrodes

ABSTRACT The present study aimed to analyse the wave morphology, amplitude, latency, and intervals of the brainstem auditory evoked responses (BAERs) in dogs with central vestibular syndrome (CVS) recorded with surface electrodes. Ten dogs with CVS were examined by mono- and binaural stimulation, using the Neuropack electrodiagnostic system, with stimulus intensities of 90 dBSPL. BAERs examinations revealed morphological changes of waves I, II, III, and V and decreased amplitudes of all waves in 7/10 dogs. P values obtained were = 0.014 for wave I amplitude, 0.031 for II, and III and 0.032 for V. Comparing the latencies of waves I, II, III, and V generated by right and left monoaural stimulation in dogs with CVS, we did not observe significant differences (P>0.05). No statistical differences were observed for BAERs latencies of the waves recorded after binaural and monaural stimulation (left or right). As far as we know, this is the first study of BAERs using surface electrodes, obtained from dogs with CVS.

Neurologic Deficits Including Auditory Loss and Recovery of Function in Horses with Temporohyoid Osteoarthropathy

BACKGROUND

Auditory loss is a common deficit in horses with temporohyoid osteoarthropathy (THO), however, recovery of function is unknown.

HYPOTHESIS/OBJECTIVES

To investigate neurologic function with emphasis in audition in horses with THO after treatment. To describe anatomical alterations of the petrous temporal bone that might result in auditory loss.

ANIMALS

Twenty-four horses with a clinical diagnosis of THO.

METHODS

Prospective study. A brainstem auditory evoked response (BAER) study was done as part of the criteria for inclusion in horses with a clinical diagnosis of THO from the years of 2005 to 2014. Physical and neurologic status and BAER findings were recorded. Brainstem auditory evoked response variables were compared by using Wilcoxon sign test. Fisher's exact test was also used. Significance was set at P < 0.05.

RESULTS

The most common signs included auditory loss (100% of horses), vestibular and facial nerve dysfunction (83%), and exposure ulcerative keratitis (71%). Concurrent left laryngeal hemiparesis was observed in 61% of horses through endoscopy. Auditory dysfunction was bilateral in 50% of the cases (complete and partial), and unilateral affecting more commonly the right ear (R = 8, L = 4). Short- and long-term follow-up revealed persistent auditory loss in all horses based on abnormal response to sound, and further confirmed through a BAER in 8 horses.

CONCLUSIONS AND CLINICAL IMPORTANCE

Auditory dysfunction appears to be a permanent neurologic deficit in horses diagnosed with THO despite overall neurologic improvement.

Brainstem auditory evoked responses in an equine patient population: part I--adult horses

Background

Brainstem auditory evoked response has been an underused diagnostic modality in horses as evidenced by few reports on the subject.

Hypothesis/Objectives

To describe BAER findings, common clinical signs, and causes of hearing loss in adult horses.

Animals

Study group, 76 horses; control group, 8 horses.

Methods

Retrospective. BAER records from the Clinical Neurophysiology Laboratory were reviewed from the years of 1982 to 2013. Peak latencies, amplitudes, and interpeak intervals were measured when visible. Horses were grouped under disease categories. Descriptive statistics and a posthoc Bonferroni test were performed.

Results

Fifty‐seven of 76 horses had BAER deficits. There was no breed or sex predisposition, with the exception of American Paint horses diagnosed with congenital sensorineural deafness. Eighty‐six percent (n = 49/57) of the horses were younger than 16 years of age. The most common causes of BAER abnormalities were temporohyoid osteoarthropathy (THO, n = 20/20; abnormalities/total), congenital sensorineural deafness in Paint horses (17/17), multifocal brain disease (13/16), and otitis media/interna (4/4). Auditory loss was bilateral and unilateral in 74% (n = 42/57) and 26% (n = 15/57) of the horses, respectively. The most common causes of bilateral auditory loss were sensorineural deafness, THO, and multifocal brain disease whereas THO and otitis were the most common causes of unilateral deficits.

Conclusions and Clinical Importance

Auditory deficits should be investigated in horses with altered behavior, THO, multifocal brain disease, otitis, and in horses with certain coat and eye color patterns. BAER testing is an objective and noninvasive diagnostic modality to assess auditory function in horses.

Brainstem auditory evoked responses in an equine patient population. Part II: foals

Background

Reports of the use of brainstem auditory evoked response (BAER) as a diagnostic modality in foals have been limited.

Hypothesis/Objectives

To describe BAER findings and associated causes of hearing loss in foals.

Animals

Study group 18 foals (15 neonatal, 3 nonneonatal), control group (5 neonatal foals).

Methods

Retrospective. BAER records from the Clinical Neurophysiology Laboratory were reviewed from the years of 1982 to 2013. Peak latencies, amplitudes, and interpeak intervals were measured when visible. Clinical data were extracted from the medical records. Foals were grouped under disease categories. Descriptive statistics were performed.

Results

Ten neonatal foals had complete absence of BAER bilaterally and 5 had findings within reference range. Abnormalities were associated with common neonatal disorders such as sepsis, neonatal encephalopathy, neonatal isoerythrolysis, and prematurity. BAER loss also was observed in foals with specific coat color patterns such as completely or mostly white with blue irides or lavender with pale yellow irides. An American Miniature foal with marked facial deformation also lacked BAER bilaterally. One nonneonatal foal with an intracranial abscess had no detectable BAER peaks bilaterally, and 2 older foals, 1 with presumed equine protozoal myeloencephalitis and the other with progressive scoliosis and ataxia, had BAER within normal limits.

Conclusions and Clinical Importance

In neonatal foals, BAER deficits commonly are complete and bilateral, and associated with common neonatal disorders and certain coat and eye color patterns. Sepsis, hypoxia, bilirubin toxicity, and prematurity should be investigated as potential causes of auditory loss in neonatal foals.

Brainstem auditory evoked potential testing in Dalmatian dogs in Brazil

The brain stem auditory-evoked potential (BAEP) is an electrophysiologic test that detects and records the electrical activity in the auditory system from cochlea to midbrain, generated after an acoustic stimulus applied to the external ear. The aim of this study is to obtain normative data for BAEP in Dalmatian dogs in order to apply this to the evaluation of deafness and other neurologic disorders. BAEP were recorded from 30 Dalmatian dogs for a normative Brazilian study. Mean latencies for waves I, III, and V were 1.14 (±0.09), 2.62 (±0.10), and 3.46 (±0.14) ms, respectively. Mean inter-peak latencies for I-III, III-V, and I-V intervals were 1.48 (±0.17), 0.84 (±0.12), and 2.31 (±0.18) ms, respectively. Unilateral abnormalities were found in 16.7% of animals and bilateral deafness was seen in one dog. The normative data obtained in this paper is compatible with other published data. As far as we know this is the first report of deafness occurrence in Dalmatian dogs in Brazil.

Estudo normativo e avaliação da influência da idade no potencial evocado auditivo em cães sem raça definida

O objetivo deste trabalho foi realizar estudo normativo dos potenciais evocados auditivos obtidos de 34 cães sem raça definida e avaliar a influência da idade nos resultados obtidos. Os animais foram divididos em dois grupos de diferentes faixas etárias e o potencial evocado auditivo foi realizado com um estímulo de 85dB. O grupo 1 incluiu 16 cães com idades entre um e oito anos e o grupo 2, 18 animais com idades acima de oito anos. O comprimento e o diâmetro da cabeça foram mensurados e não houve diferença estatística entre os dois grupos. No grupo 1, as médias das latências das ondas I, III e V foram: 1,13; 2,64 e 3,45ms; e dos intervalos I-III, III-V e I-V foram 1,51; 0,81 e 2,32ms, respectivamente. No grupo 2, as médias das latências das ondas I, III e V foram 1,15; 2,62 e 3,55ms; e dos intervalos I-III, III-V e I-V foram 1,47; 0,93 e 2,40ms, respectivamente. As latências observadas neste estudo foram semelhantes a estudos prévios realizados por outros autores. Nos grupos etários analisados e nas condições preestabelecidas deste estudo, a idade influenciou a latência da onda V e, consequentemente, modificou os intervalos III-V e I-V, portanto deve-se considerar essa variante na interpretação dos resultados do BAEP em cães.

Magnetic resonance imaging and brainstem auditory evoked responses in the diagnosis of cerebellar cortical degeneration in american staffordshire terriers

The aim of the study was to determine the diagnostic usefulness of magnetic resonance imaging (MRI) and brainstem auditory evoked responses (BAER) in dogs suspected of having cerebellar cortical degeneration (CCD). In the years 2009-2011, six dogs with suspected CCD were examined. Both MRI and BAER examinations revealed abnormalities in all dogs (100%). By MRI, T2-weighted midsagittal images revealed an increased amount of cerebrospinal fluid (CSF) surrounding the cerebellum within the sulci of the folia in all dogs (100%). In 4 out of the 6 dogs (66.66%), cerebellar hypoplasia was more visible in the region of the dorsal cerebellar lobules. In 5 out of the 6 dogs (83.33%), the fourth ventricle was enlarged. In our studies, the brain to cerebellum ratio evaluated on the midsagittal image was 11.93%, in comparison to 14.9% in normal dogs. By BAER examination, the amplitude of the first and second waves was diminished and III-V interlatency was prolonged in 5 out of the 6 dogs (83.33%). In one out of the 6 dogs (16.67%), only the III-V interlatency was prolonged. In one dog (16.67%), somato-nervous deafness in the left ear was detected, whereas in the right ear the III-V interlatency was prolonged. MRI of the cerebellum is a reliable method for the antemortem diagnosis of CCD in American Staffordshire terriers, as is BAER examination. BAER is an objective diagnostic tool, which - along with other diagnostic modalities - can be helpful in the assessment, management and follow-up of dogs with cerebellar abiotrophy. It proved to be useful in determining the severity of neurological lesions in comparison to MRI findings, as well as in assessing the prognosis.

Effect of middle ear effusion on the brain-stem auditory evoked response of Cavalier King Charles Spaniels

Brain-stem auditory evoked responses (BAER) were assessed in 23 Cavalier King Charles Spaniels with and without middle ear effusion at sound intensities ranging from 10 to 100 dB nHL. Significant differences were found between the median BAER threshold for ears where effusions were present (60 dB nHL), compared to those without (30 dB nHL) (P=0.001). The slopes of latency-intensity functions from both groups did not differ, but the y-axis intercept when the x value was zero was greater in dogs with effusions (P=0.009), consistent with conductive hearing loss. Analysis of latency-intensity functions suggested the degree of hearing loss due to middle ear effusion was 21 dB (95% confidence between 10 and 33 dB). Waves I-V inter-wave latency at 90 dB nHL was not significantly different between the two groups. These findings demonstrate that middle ear effusion is associated with a conductive hearing loss of 10-33 dB in affected dogs despite the fact that all animals studied were considered to have normal hearing by their owners.

Brainstem auditory evoked potentials in experimentally-induced bovine spongiform encephalopathy

This study was carried out to evaluate the features of neurological dysfunction in experimentally-induced bovine spongiform encephalopathy (BSE)-infected cattle using brainstem auditory evoked potentials (BAEP). The progressive prolongation of peak latency of waves III and V was observed right-and-left bilaterally at the onset of neurological symptoms. The peak latency of wave V and the I-V interpeak latency (IPL) in BSE cattle 22 and 24 months after intracerebral inoculation were significantly (P<0.05) prolonged compared with the control cattle. In addition, the amplitude of the BAEP waves of the BSE cattle were low compared with the control cattle. Hearing loss occurred in the BSE cattle that showed advanced neurological symptoms such as tremor. It is thought that this BAEP data reflects a functional disorder in the central auditory nerve pathways characteristic of experimentally-induced BSE.

Frequency-specific electric response audiometry (ERA) and its clinical application in the diagnosis of hearing defects in the dog

Reference values were established for frequency-specific electric response audiometry (ERA) in dogs on the basis of the results of ERA examinations of 200 animals with normal hearing. Air-conducting acoustic tubes with foam stoppers were used in the determination of the following: the latencies of waves I, III and V; interpeak latencies (IPL) I-III, III-V and I-V; amplitudes I and V; and the amplitude difference I-V. A frequency-specific stimulus (tone pip) was used for frequency-specific examination (1 to 4 kHz) over the entire frequency range indicated. These reference values were then used for the clinical examination of 50 dogs with hearing defects. A frequency-specific ERA was conducted and the results evaluated. These findings made it possible to draw objective conclusions about the degree, type and site of the hearing defects. Frequency-specific electric response audiometry was shown to be an important diagnostic tool for the detection of partial high- and low-frequency hearing loss and for the characterisation of hearing defects of otological, otoneurological and neurological origin.

Vestibular signs associated with suspected lightning strike in two horses

Two previously healthy 14-year-old horses developed right-sided unilateral vestibular signs after they had possibly been struck by lightning. Repeated radiographic and endoscopic evaluations did not reveal any significant changes. A brainstem auditory evoked response test indicated a subtle left to right interaural latency difference of waves I, III and V in the more severely affected pony, but its central conduction time remained normal.

Results of magnetic resonance imaging in dogs with vestibular disorders: 85 cases (1996-1999)

OBJECTIVE

To determine results of magnetic resonance (MR) imaging in dogs with vestibular disorders (VD) and correlate results of MR imaging with clinical findings.

DESIGN

Retrospective study.

ANIMALS

85 dogs.

PROCEDURE

Information on signalment, clinical signs, and presumptive lesion location was obtained from the medical records, and MR images were reviewed.

RESULTS

27 dogs had peripheral VD, 37 had central VD, and 21 had paradoxical VD. Of the 27 dogs with peripheral VD, 11 (41%) had MR imaging abnormalities involving the ipsilateral tympanic bulla compatible with otitis media (6 also had abnormalities involving the petrous portion of the ipsilateral temporal bone compatible with otitis interna), 7 (26%) had MR imaging abnormalities compatible with middle ear neoplasia, 2(7%) had an ipsilateral cerebellopontine angle lesion, and 7 (26%) did not have MR imaging abnormalities. All dogs with central and paradoxical VD had abnormalities evident on MR images. Of the 37 dogs with central VD, 13 (35%) had an extra-axial lesion, 6 (16%) had an intra-axial lesion, and 18 (49%) had multiple intra-axial lesions. In 23 (62%) dogs with central VD, lesions on MR images corresponded with location suspected on the basis of clinical signs. Of the 21 dogs with paradoxical VD, 12 (57%) had an extra-axial lesion, 5 (24%) had an intra-axial lesion, and 4 (19%) had multiple intra-axial lesions. Location of lesions on MR images agreed with location suspected on the basis of clinical signs in 19 (90%) dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that MR imaging may be helpful in the diagnosis and treatment of VD in dogs.

Ventral surgical approach to the caudal brain stem in dogs

OBJECTIVE

To develop a safe neurosurgical procedure that accessed the ventral pons and medulla of the dog primarily for the removal of brain stem neoplasms.

STUDY DESIGN

In vivo study.

METHODS

A cadaver study was performed on mesocephalic dog heads to develop a neurosurgical approach to the ventral brain stem. Based on this study, an approach to the ventral brain stem was developed by basioccipital craniectomy. This procedure was performed on 4 young neurologically normal Beagle dogs to assess morbidity and mortality associated with the procedure. Morbidity was evaluated by subjective criteria, daily complete neurologic examinations, comparison of preoperative and postoperative brain stem auditory evoked response (BAER) tests, and postmortem examinations.

RESULTS

Three dogs developed a transient cough but were neurologically normal after surgery. One dog was euthanatized within 12 hours of surgery because of severe postoperative morbidity associated with basilar artery disruption due to improper development of the craniectomy. Prolongations of postoperative BAER latencies were observed in 2 dogs but did not appear to be associated with clinical deficits or histopathologic changes in the brain stem. Minimal histopathologic changes were observed except in the dog with basilar artery disruption. Results of this study indicate that, although technically challenging, this procedure can be performed with minimal morbidity.

CLINICAL IMPLICATIONS

The main indication for this procedure is surgical reduction or biopsy of ventrally located brain stem neoplasms in dogs. The major disadvantage is anatomic restrictions that prevent access to laterally oriented ventral brain stem masses.

Current concepts in the diagnosis and treatment of brain tumours in dogs and cats

Intracranial tumours occur relatively frequently in dogs, and less commonly in cats. With the availability of computed tomography (CT) and magnetic resonance imaging, more accurate determination of the location and extent of brain tumours in companion animals has become possible. Following these advances in imaging, precise CT-guided stereotactic techniques for both tumour biopsy and intratumoral drug delivery have been developed for use in cats and dogs. Also, tumour identification methods, such as crush preparation examination, have facilitated rapid tumour identification. The use of improved diagnostic techniques has resulted in an increasing demand for effective therapies for brain tumours. While surgical removal and irradiation remain important treatment considerations in the management of brain tumours of cats and dogs, the development of gene therapy strategies for treatment of intracranial tumours offers much promise, although research in this area is still at an early stage.

Brainstem auditory evoked responses elicited by tone-burst stimuli in clinically normal dogs

Brainstem auditory evoked responses (BAERs) to click and tone-burst stimuli (0.5, 1, 2, 4, and 8 kHz) were recorded from 32 ears in 16 adult Beagles. BAERs were used to establish a normative database and describe response thresholds and latencies (wave I-IV) for the different stimuli. The frequencies of sound used were 8, 4, 2, 1, and 0.5 kHz. Sound stimuli were delivered by a closed headphone and masking stimuli were not applied. The BAER waveforms obtained were similar to those reported previously, except for a frequency-following response evoked by 1-kHz tone-bursts. The threshold was lowest when clicks and 4-kHz tone-bursts were used. Significant differences were observed between the mean values of the peak latencies for clicks and 4- and 8-kHz tone-bursts. The tone-burst stimulation used in our experiment was shown to be an appropriate method for detecting the BAERs. Thus, for investigating the frequency-specificity of the auditory sense, BAER data obtained using tone-burst sound in dogs may be meaningful.