Deafness in Cavalier King Charles Spaniels
Can be Congenital or Progressive
- What It Is
- -- Congenital Deafness
- -- Progressive Deafness
- -- PSOM
- -- PSOM as a differential diagnosis
- Breeders' Responsibilities
- What You Can Do
- Research News
- Related Links
- Veterinary Resources
Cavalier King Charles spaniels are predisposed to a form of congenital deafness, although it is not as common in cavaliers as it is in a few other breeds. Congenital deafness is present at birth, due to a lack of formation or early degeneration of receptors in the inner ear.
In addition, studies by Dr. Michael Podell (right) have found cavaliers which develop a progressive hereditary hearing loss, which usually begins during puppyhood and worsens, or progresses, until the dog is completely deaf, usually between the ages of three and five years. The progressive nature of this form of deafness in CKCSs is believed to be due to degeneration of the hearing nerve, rather than the lack of formation or early degeneration of the inner ear receptors. Dr. Podell also has referred this disorder as abiotrophic sensorineural deafness and has described it as an inherited congenital sensorineural deafness which affects hair cells of the spiral organ. Dr. Podell is an ACVIM board certified veterinary neurologist and was an associate professor of neuroscience and veterinary medicine at the Ohio State University at the time of his studies.
Another ear disorder becoming more common in cavaliers is Primary Secretory Otitis Media (PSOM), also called "glue ear", which can produce a conductive hearing loss, due to the mucus plug which PSOM produced in the dog's inner ear. The mucus accumulation in the middle ear results in loss of conduction of sound waves which reduces the ability of the middle ear bones to transfer the sound wave energy to the inner ear hearing apparatus, the cochlea. As such, the first signs are often related to changes in hearing threshold, with many dogs responding to louder noises only. Over time, complete hearing loss may occur. PSOM is discussed at length on its own webpage.
The conventional manner of testing a dog's hearing is the BAER (for Brainstem Auditory Evoked Response) test. The BAER test provides an objective assessment of auditory function in canines and other animals. The BAER test objectively examines a dog's hearing by bypassing the need to rely subjectively on the patient's response. (The ruby cavalier at right is undergoing a BAER test.)
BAER measures the timing of electrical waves from the brain stem in response to a click, as a sound stimulus, in the ear. Within milliseconds of each click being made in a hearing dog's ear, a series of standard electrical waves appear on the BAER instrument's screen. The first wave comes from a nerve which transmits sound information to the brain. Then three or four other waves come from the areas of the brain stem which generate the hearing signal to the front of the brain and then to the cerebrum where the signal is interpreted as a sound. If the dog cannot hear the clicks, the waves will not appear on the screen. There are two types of BAER tests, air-conducted and bone-conducted. (Below is a BAER scan of a cavalier with hearing loss.)
However, conventional BAER testing usually does not adequately identify cavaliers with progressive hearing deficiencies, because most BAER sites test only from a sound intensity threshold of 70 to 90 decibels, which is about the level of the sound of a vacuum cleaner next to the ear. The human voice normally is at the 60 dB intensity level, so even a cavalier which passes the conventional BAER test could be deaf to human voices and levels of normal daily sounds. Therefore, BAER tests of cavaliers should be at as low a decibel intensity threshold as possible – no higher than 30 dB.
CKCSs may be tested as early as eight weeks of age for congenital deafness, once the puppies’ ear canals are completely open. However, the condition of progressive hearing loss – due to degeneration of the hearing nerve – has a later onset and cannot be detected in young puppies.
Primary secretory otitis media (PSOM) is frequently diagnosed in cavalier King Charles spaniels, and the mucus plug, which PSOM creates in the inner ear, can cause a conductive hearing loss. BAER testing is able to diagnose hearing losses, but it can be inconclusive as to whether the dog has a conductive hearing loss or a sensorineural hearing loss or a combination of the two. Therefore, if a cavalier is suspected to have impaired hearing, it is necessary to determine if the hearing loss is conductive (with a likely cause of PSOM) or sensorineural (due to abiotrophic sensorineural deafness), or both.
To do this, hearing specialists typically will evaluate for PSOM using the standard procedures discussed on its webpage. Briefly, this consists of first performing an otic examination by manually using an otoscope. If that exam does not show that the top part of the ear drum is bulging (indicating PSOM), then the veterinarian will do a computed tomography (CT) scan or a magnetic resonance imaging (MRI) scan under anesthesia, still trying to diagnose or eliminate PSOM.
If the cavalier has PSOM, the specialist then normally will perform the two BAER tests (air-conducted and bone-conducted) after the scan, to see if there is hearing loss and try to assess whether it is conductive or sensorineural. If the cavalier does not have PSOM, the likelihood of a conductive hearing loss will be discounted, and the specialist will perform the air-conducted BAER test. If that test diagnoses that the dog's hearing is impaired, the hearing loss would be classified as sensorineural.
No cavalier suffering from an hereditary hearing deficiency should be bred. BAER testing should be conducted at no younger than age 2.5 years, and at the low decibel intensity threshold of 30 dB, to assure that the cavaliers do not suffer from the hereditary disease of deafness which they would pass along to their litters.
There is a possibility that any cavalier will become deaf or partially deaf. You can prepare for this possibility by learning how to communicate with your dog by alternative ways, especially hand signals and purposeful body motions. If a dog knows how to otherwise understand what you expect of him, before he becomes deaf, then communicating with him after he loses his hearing will be much easier.
There are books and websites which offer helpful advice in communicating with deaf dogs. An excellent such book is Living With a Deaf Dog: A Book of Advice, Facts and Experiences About Canine Deafness by Susan C. Becker. An excellent website is DeafDogs.org
In the meantime, keep your dogs' ears clean. Here is a YouTube video that shows how it can be done.
July 2014: UK's Dr. Jacques Penderis finds MRI noise results in some hearing loss in dogs. In a study of 36 dogs, a Univerisity of Glasgow team lead by Dr. Jacques Penderis found that exposure to noise during MRI scans results in significant reductions in cochlear function at five of fourteen frequencies. It is not known whether the hearing loss is reversible or permanent. See more details in the November 2013 entry below.
November 2013: Univ. of Glasgow thesis reports MRI noise causes hearing loss and reduced cochlear function in dogs. In a 2013 Master of Science (Research) thesis at the University of Glasgow, Rebecca Elisabeth Venn reports that all of 36 dogs (including four cavalier King Charles spaniels) which underwent MRI scans, experienced reduced cochlear function and more than half of the 36 dogs had hearing loss using Distortion Product Otoacoustic Emissions (DPOAE) testing. Ms. Venn noted that the post-MRI testing was not repeated weeks after the MRIs, so it is not known if the hearing loss was temporary or permanent. She also noted that evidence from human MRI noise exposure suggests that the hearing loss is temporary. She recommends that "all dogs having MRI studies performed should have ear protection as a standard precautionary measure." See also the July 2014 entry above.
September 2012: UK Dr. Gert ter Haar heads RVC's new ear, nose, and throat clinic. UK's Royal Veterinary College has commenced an ear, nose, and throat referral clinic at the Queen Mother Hospital for Animals in London. Dr. Gert ter Haar heads the unit, which offers services including advanced diagnostics and treatment for PSOM in cavaliers, as well as CT and BAER diagnostics for deafness (plus hearing aid implants for selected patients), and diagnostics and treatment of cavaliers with brachycephalic airway obstruction syndrome (BAOS). Telephone 01707 666 365 for more information.
May 2012: OSU’s Dr. Cole needs normal hearing CKCSs for BAER tests, CT scans, and MRI scans. Dr. Lynette Cole (right) of Ohio State University’s Veterinary Dermatology and Otology Service needs cavaliers between the ages of 1 to 2 years old with no history of hearing loss for a two-day evaluation by BAER hearing tests, computed tomography (CT) scans, and MRI scans. The study pays for all testing. She writes:
“In the dog breed Cavalier King Charles Spaniel (CKCS), hearing disorders may be due to conductive hearing loss, which may occur with primary secretory otitis media (PSOM), or due to sensorineural hearing loss, which may occur when there is damage or an abnormality of the sensory cells in the cochlea or the auditory nerve.”
If you are interested in possibly enrolling your cavalier in the study, contact Dr. Cole at telephone number 614-292-3551 or email firstname.lastname@example.org. Click here for the OSU webpage. A pedigree is required for entry into the study, but will be kept confidential, as will all test results. Details of the study will be given individually on the phone or via email.
April 2011: Researchers seek DNA swabs to study hearing loss in cavaliers. The Canine Genetics Group at the Van Andel Research Institute and the Translational Genomics Research Institute is studying DNA patterns that contribute to hearing loss in the CKCS. Thus far, the group has identified such DNA patterns for four other breeds.
If you have a cavalier suspected of hearing loss, a saliva sample is all the group needs for the study. If you have an older cavalier with good hearing, the study needs DNA from those dogs, too, for "control" purposes. To obtain a free DNA kit, contact the Program for Canine Health and Performance at email@example.com Include your mailing address and tell them the number of kits you need for both affected cavaliers and healthy cavaliers. Blood samples from affected CKCSs, drawn by veterinarians, also are needed. Contact Elissa Boguslawski at firstname.lastname@example.org for blood sample submission instructions.
Investigation of hearing impairment in Cavalier King Charles spaniels, using auditory brainstem response audiometry Munro, K.J., Cox, C.L. J. Small Animal Prac.1997,38:2-5. "Quote: "Auditory brainstem response audiometry was used to investigate nine Cavalier King Charles spaniels with a history of hearing impairment. Successful recordings were made in all cases. In eight of the dogs, the hearing impairment was between 40 and 85 decibels re normal hearing level. In addition to confirming the degree of impairment in each ear, information was obtained concerning the site of the lesion. The auditory brainstem technique may have an important role to play in assessing treatment outcome. Other applications include screening animals used in breeding programmes as well as working dogs requiring good binaural hearing."
Hearing Assessment in Cavaliers. Podell, M. CKCSC,USA Bulletin, Fall 1998; p. 21. Quote: "Deafness is an increasingly recognized problem of a number of pure-bred dogs, and more recently, has been documented as a congenital problem in the Cavalier King Charles Spaniel. Hearing loss may be due to a problem conducting sound waves through the middle ear (conductive loss) or to a problem related to the hearing receptors or nerve in the inner ear (sensorineural hearing loss). Conductive hearing loss usually is a problem related to ear infection(s) or aging. Sensorineural hearing loss occurs most commonly as a congenital disease; that is, the condition is present from birth. The loss can be complete, leading to deafness, or partial, leading to abnormal hearing function. ... Recently, a new finding has emerged in studying congenital deafness in Cavaliers. Rather than present with complete hearing loss in one or both ears, a particular line of dogs has developed a progressive hearing loss as they matured over first few years of life. These dogs were documented to have a normal BAER test as young puppies, using standard testing. However, over time, the dogs developed significant hearing loss, even to the point of being deaf. This type of hearing loss may be quite different from that of other breeds, in that the hearing nerve may be degenerating, rather than failure of formation or early degeneration of the inner ear receptors. This type of hearing loss may be similar to that seen in progressive nerve degeneration in young children and adolescents. This condition presents a unique problem in that puppies may test completely normal, and then be found to develop later onset hearing nerve degeneration after already passing on a potentially inherited disorder."
Congenital Deafness and Its Recognition. Strain, G.M. Veterinary Clinics of N.A.: Small Animal Practice - Spec. Iss., Pediatrics - July, 1999. (Includes CKCSs).
Advances in assessing canine degenerative hearing loss. M. Podell. Proc Am Coll Vet Intern Med. 1999; 17:291-293.
Pet Care in the New Century: Cutting-Edge Medicine for Dogs and Cats. Shojai, AD. 2001, New Amer Library, p.185. Quote: "Dr. Michael Podell ... reports that a particular line of CKCSs seems to present a new type of deafness. Instead of the more typical complete hearing loss in one or both ears from birth, puppies have normal hearing at birth and develop a progressive hearing loss over the first few years of life, even to the point of becoming deaf. Dr. Podell suspects this type of hearing loss is caused by degeneration of the hearing nerve. The new condition poses a problem in screening such dogs to keep potential breeders from passing on the tendency to their offspring. Further studies are underway to identify tests that may be useful in predicting which dogs may develop such a hearing problem."
Deafness prevalence and pigmentation and gender associations in dog breeds at risk. George M. Strain. Vet. J. 2004; 167:23–32. (Includes CKCSs).
Veterinary Neuroanatomy and Clinical Neurology. Alexander de Lahunta, Eric N. Glass. Saunders 3d edit. July 2008; 438. Quote: "Congenital abiotrophic sensorineural deafness directly affects the hair cells in the spiral organ. ... The lesion is usually bilateral and occasionally also affects the hair cells of the vestibular system receptors. The inheritance usually involves an autosomal recessive gene. Although most of these abiotrophies cause deafness at a few weeks of age, occasionally the onset of deafness occurs later in life. In the cavalier King Charles spaniel, deafness may not be apparent until 3 or 4 years of age."
A Practical Guide to Canine and Feline Neurology. Curtis W. Dewey. John Wiley & Sons; 2008; 4-6. "Breed-associated neurologic abnormalities of dogs and cats. ... Cavalier King Charles Spaniels ... Congenital deafness."
Canine Inherited Disorders Database: http://www.upei.ca/~cidd/Diseases/nervous system disorders/deafness.htm
Post-anesthesia deafness in dogs and cats following dental and ear cleaning procedures. Cathryn K. Stevens-Sparks, George M. Strain. Vet. Anaesthesia & Analgesia. July 2010;37(4):347-351. Quote: "Objective: The present study was performed to document hearing loss in dogs and cats following procedures performed under anesthesia. Most cases of reported hearing loss were subsequent to dental and ear cleaning procedures. Study design: Prospective and retrospective case survey. Animals: Subjects were dogs and cats with deafness, personally communicated to one author, cases discussed on a veterinary information web site, and cases communicated through a survey of general practice and dental specialist veterinarians. Methods: Reported deafness cases were characterized by species (dog, cat), breed, gender, age, and dog breed size. Results: Sixty-two cases of hearing loss following anesthesia were reported between the years 2002 and 2009. Five additional cases were reported by survey respondents. Forty-three cases occurred following dental procedures. Sixteen cases occurred following ear cleaning. No relationship was observed between deafness and dog or cat breed, gender, anesthetic drug used, or dog size. Geriatric animals appeared more susceptible to post-anesthetic, post-procedural hearing loss. Conclusions: Deafness may occur in dogs and cats following anesthesia for dental and ear cleaning procedures, but the prevalence is low. The hearing loss appears to be permanent."
Deafness in Dogs & Cats. Strain, G.M. Nov. 2011. (Includes CKCSs).
Canine Deafness. George M. Strain. Vety.Clinics.Sm.Anim.Pract. Oct.2012. Quote: "Conductive deafness, caused by outer or middle ear obstruction, may be corrected, whereas sensorineural deafness cannot. Most deafness in dogs is congenital sensorineural hereditary deafness, associated with the genes for white pigment: piebald or merle. The genetic cause has not yet been identified. Dogs with blue eyes have a greater likelihood of deafness than brown-eyed dogs. Other common forms of sensorineural deafness include presbycusis, ototoxicity, noise-induced hearing loss, otitis interna, and anesthesia. Definitive diagnosis of deafness requires brainstem auditory evoked response testing."
Electrodiagnostic Evaluation of Auditory Function in the Dog. Peter M. Scheifele, John Greer Clark. Vet.Clinics of N.A.:Sm.Anim.Prac. Nov. 2012; 42(6):1241-1257. Quote: "Given the high incidence of deafness within several breeds of dogs, accurate hearing screening and assessment is essential. In addition to brainstem auditory evoked response (BAER) testing, 2 other electrophysiologic tests are now being examined as audiologic tools for use in veterinary medicine: otoacoustic emissions and the auditory steady state response (ASSR). To improve BAER testing of animals and ensure an accurate interpretation of test findings from one test site to another, the establishment of and adherence to clear protocols is essential. The ASSR holds promise as an objective test for rapid testing of multiple frequencies in both ears simultaneously."
Canine Brainstem Auditory Evoked Responses are not Clinically Impacted by Head size or Breed. Debra L. Kemper, Peter M. Scheifele, John Greer Clark. Physiology & Behavior. Feb. 2013. 110-111:190-197. Quote: "Accurate assessment of canine hearing is essential to decrease the incidence of hereditary deafness in predisposed breeds and to substantiate hearing acuity. The Brainstem Auditory Evoked Response (BAER) is a widely accepted, objective test used in humans and animals for estimation of hearing thresholds and deafness diagnosis. In contrast to humans, testing and recording parameters for determination of normal values for canine hearing are not available. Conflicting information concerning breed and head size effects on canine BAER tests are major contributors preventing this normalization. The present study utilized standard head measurement techniques coupled with BAER testing and recording parameters modeled from humans to examine the effect canine head size and breed have on BAER results. Forty-three adult dogs from fourteen different breeds [including the cavalier King Charles spaniel] had head size measurements and BAER tests performed. The mean latencies compared by breed for waves I, II, III, IV, and V were as follows: 1.46±0.49msec, 2.52±0.54msec, 3.45±0.41msec, 4.53±0.83msec and 5.53±0.43msec, respectively. The mean wave I-V latency interval for all breeds was 3.69msec. All dogs showed similar waveform morphology, structures, including the presence of five waves occurring within 11 milliseconds after stimulus presentation and a significant trough occurring after Wave V. All of the waveform morphology for our subjects occurred with consistent interpeak latencies as shown by statistical testing. All animals had diagnostic results within the expected ranges for each wave latency and interwave interval allowing diagnostic evaluation. Our results establish that neither differences in head size nor breed impact determination of canine BAER waveform morphology, latency, or hearing sensitivity for diagnostic purposes. The differences in canine head size do not have a relevant impact on canine BAERs and are not clinically pertinent to management or diagnostic decisions."
The Effects of Magnetic Resonance Imaging Noise on Cochlear Function in Dogs. Chapter 2 of "Effects of acute and chronic noise exposure on cochlear function and hearing in dogs." Rebecca Elisabeth Venn. MSc(R) thesis pp 21-42, University of Glasgow. 2013. Quote: "In specialised veterinary hospitals, Magnetic Resonance Imaging (MRI) scanners are used daily in diagnostics of dogs. MRI scanners omit high levels of acoustic noise, which is known to be damaging to the hearing of human patients without effective ear protection. However, the effects of the MRI noise levels on the cochlear function and hearing of dogs is often overlooked and in many clinics, dogs are not provided with ear protection for the duration of their scan. The aim of this study was to assess the effects of MRI acoustic noise on the cochlear function of dogs, by Distortion Product Otoacoustic Emissions (DPOAE) testing dogs immediately before and after they underwent an MRI scan. ... Thirty-six dogs were included in the MRI group (mean age 3.9 years, median age 3 years, range 6 months to 10 years; mean bodyweight 16.9 kg, median bodyweight 13.8 kg, range 3.5 kg to 40.8 kg) and 17 dogs were included in the control group (mean age 6.2 years, median age 7 years, range 1 year to 12 years; mean bodyweight 25.1 kg, median bodyweight 23.6 kg, range 6.7 kg to 57.8 kg). There were 16 male dogs in the MRI group (44.4%) and 10 male dogs in the control group (58.8%). A variety of dog breeds were represented, with those represented more than once including three toy poodles, three Lhasa Apso dogs, four Labrador retrievers, two cocker spaniels, four Cavalier King Charles spaniels, two boxers and three cross-breeds in the MRI group, and two Labrador retrievers and two cross-breeds in the control group.... A group of control dogs undergoing a quiet procedure (but treated with the same range of anaesthetic drugs) were also tested. Post-MRI, the mean DPOAE of the dogs was reduced at all frequencies tested, significantly so at five (out of fourteen) frequencies, reflecting a reduction in cochlear function. Furthermore, at all frequencies tested, more than half of the ears exposed to MRI noise demonstrated a decrease in DPOAE. ... The results from this study indicate that exposure to noise during MRI in dogs results in a reduction in cochlear function, which is significant at multiple sound frequencies. ... Without repeat DPOAE testing of the dogs some weeks after their MRI, it is unknown whether this effect is temporary and reversible, or permanent. ... Evidence from human MRI noise exposure would suggest that this effect is temporary. The frequency region affected is likely influenced by the frequency of the noise spectra of the MRI. The demonstration that MRI noise results in some degree of hearing loss, albeit only assessed in the immediate post-MRI period in the present study, would suggest that all dogs having MRI studies performed should have ear protection as a standard precautionary measure."
The Canine Jaw-Ear Connection: The Malleomandibular and Tympanomandibular Ligaments. Cathryn Stevens-Sparks, George M. Strain. Anat. Rec. May 2014;297(5):876-891. Quote: "In the human, two ligaments derived from the first embryonic pharyngeal (branchial) arch that unite the mandible and temporomandibular joint (TMJ) with the middle ear have been identified as the discomalleolar ligament (DML) and sphenomandibular ligament (SML), also known as the malleomandibular ligament (MML), anterior ligament of the malleus (AML), and tympanomandibular ligament (TML). Neither of these structures has been previously described in the dog. The homologue of the human sphenomandibular ligament (SML) exists in the dog and is represented as a fibrous remnant of Meckel's cartilage. In the newborn puppy, the ligament is a true malleomandibular ligament (MML), extending from the medial mandible to the rostral process of the malleus with no intermittent attachments. In the adult dog, the ligament is entrapped within a bony passageway, likely due to the development and ossification of the tympanic bulla, making it difficult to grossly view the complete course of the ligament. The majority of the ligamentous fibers attach near the tympanic bulla in the adult dog, thus this portion of the ligament has been named the tympanomandibular ligament (TML). Those fibers of the ligament not attaching near the tympanic bulla appear to continue through a canal, located between the tympanic annulus and the surrounding tympanic bone, to become continuous with a connective tissue sheet within the cavity of the middle ear that has attachments to the malleus and incus. Tension on the adult canine TML did not result in movement of the malleus."
The effect of magnetic resonance imaging noise on cochlear function in dogs. R.E. Venn, A.R. McBrearty, D. McKeegan, J. Penderis. Vet.J. July 2014. Quote: "Noise produced by magnetic resonance imaging (MRI) scanners (which can peak at a sound pressure level of 131 dB) has been shown to cause noise-induced cochlear dysfunction in people. The aim of this study was to investigate whether noise produced during MRI had a deleterious effect on cochlear function in dogs, using distortion product otoacoustic emission (DPOAE) testing, which allows frequency specific, non-invasive assessment of cochlear function. A control group comprised dogs undergoing anaesthesia of a similar duration for quiet procedures. Thirty-six dogs (66 ears) and 17 dogs (28 ears) were included in the MRI and control groups respectively. There was a reduction in DPOAE at all frequencies tested in the MRI group; a similar effect was not evident in the control group. This reduction in the MRI group was statistically significant in five of the 14 frequencies assessed (P<0.05). Exposure to noise during MRI in dogs results in a significant reduction in cochlear function, although it is not known whether this is reversible or permanent. The frequency region affected is probably influenced by the frequency of the noise spectra of the MRI. The finding that MRI noise results in hearing loss, albeit only assessed in the immediate post-MRI period, would suggest that all dogs undergoing MRI studies should have ear protection as a standard precaution. What is not evident from the present study is the longer-term effect of excessive MRI noise on hearing and further studies are also required to assess the efficacy of ear protection to protect against the effects of MRI noise in dogs." (See also the 2013 Rebecca Elisabeth Venn master's thesis above.)
The genetics of deafness in domestic animals. George M. Strain. Frontiers in Vet. Sci. September 2015. Quote: "Although deafness can be acquired throughout an animal’s life from a variety of causes, hereditary deafness, especially congenital hereditary deafness, is a significant problem in several species. Extensive reviews exist of the genetics of deafness in humans and mice, but not for deafness in domestic animals. Hereditary deafness in many species and breeds is associated with loci for white pigmentation, where the cochlear pathology is cochleo-saccular. In other cases, there is no pigmentation association and the cochlear pathology is neuroepithelial. Late onset hereditary deafness has recently been identified in dogs and may be present but not yet recognized in other species. Few genes responsible for deafness have been identified in animals, but progress has been made for identifying genes responsible for the associated pigmentation phenotypes. Across species, the genes identified with deafness or white pigmentation patterns include MITF, PMEL, KIT, EDNRB, CDH23, TYR, and TRPM1 in dog, cat, horse, cow, pig, sheep, ferret, mink, camelid, and rabbit. Multiple causative genes are present in some species. Significant work remains in many cases to identify specific chromosomal deafness genes so that DNA testing can be used to identify carriers of the mutated genes and thereby reduce deafness prevalence. ... Cavalier King Charles spaniels: A form of late onset conductive hearing loss known as primary secretory otitis media (PSOM) appears in Cavalier King Charles spaniels, although at least one case each has also been reported in a Dachshund, a boxer, and a Shih Tzû. No proven hereditary cause has been identified, but the preponderance of occurrence in the one breed supports this as a possible factor. Several single-gene otitis media-causing mouse mutants have been identified and there is a suggestion of a hereditary component in OM in humans. A correlation between PSOM and pharyngeal conformation has been suggested, possibly from a thick soft palate and reduced nasopharyngeal aperture, which might argue against a hereditary basis. Because the phenotype of the Cavalier includes white pigment that probably results from a recessive allele of the S locus, affected dogs may incorrectly be thought to exhibit the congenital CS pathology. Primary secretory otitis media, also known as glue ear, results from the development of a solid viscous plug in the middle ear due to either increased production of mucus by the middle ear lining or reduced drainage through the auditory (Eustachian) tube. Signs include hearing loss, neck scratching, otic pruritus, head shaking, abnormal yawning, head tilt, facial paralysis, or vestibular disturbances. Testing has confirmed that the hearing loss is conductive. Implantation of tympanostomy tubes has been successful in a small number of cases, but treatment is typically by myringotomy followed by flushing of the mucus plug, repeated as needed. No studies have been reported of genetic association studies."