Abstract
Objective—To determine the prevalence of nonneoplastic middle ear disease among cats undergoing necropsy and the prevalence of clinical abnormalities in cats in which nonneoplastic middle ear disease was identified.
Design—Retrospective case series.
Animals—59 cats that underwent necropsy between January 1991 and August 2007.
Procedures—Medical records were searched to identify cats in which nonneoplastic middle ear disease was identified at necropsy. For cats included in the study, data that were recorded included signalment, initial complaint, whether the cat had any clinical signs of middle or external ear disease, whether the cat had upper respiratory tract disease, necropsy diagnosis, gross appearance of the bullae, and reason for euthanasia. Signs of middle ear disease that were considered included unilateral peripheral vestibular disease without motor deficits, Horner syndrome, and facial nerve paralysis.
Results—Of the 3,442 cats that underwent necropsy during the study period, 59 (1.7%) had nonneoplastic middle ear disease. Six of the 59 (10%) cats, including 1 cat that was affected bilaterally, had clinical signs of middle ear disease. Of these, 5 had signs of unilateral peripheral vestibular disease, and 1 had Horner syndrome.
Conclusions and Clinical Relevance—Results suggested that most cats with nonneoplastic middle ear disease did not have associated clinical signs. Findings may be of clinical relevance for cats in which middle ear disease is identified as an incidental finding during computed tomography or magnetic resonance imaging for unrelated diseases.
With the increasing availability of computed tomography and magnetic resonance imaging, advanced diagnostic imaging is being performed more frequently in cats with cranial trauma, dental disease, nasal disease, intracranial disease, and other disorders of the head. When the tympanic bullae are included in these studies and abnormalities of the middle ear are identified as an incidental finding, a decision must be made as to whether to pursue additional diagnostic testing or treatment. However, treatment of middle ear disease in cats, which primarily involves surgery, is not without potential complications. Thus, additional information on the clinical importance of middle ear disease in cats would be useful.
The prevalence of middle ear disease in cats is not well documented, with, to the authors' knowledge, only a single study1 having reported on the incidence of middle ear disease in cats undergoing necropsy. However, not only was that study performed several decades ago, but it also did not provide information on how many cats with middle ear disease had clinical abnormalities. The purpose of the study reported here, therefore, was to determine the prevalence of nonneoplastic middle ear disease among cats undergoing necropsy and the prevalence of clinical abnormalities in cats in which nonneoplastic middle ear disease was identified.
Materials and Methods
Case selection criteria—Necropsy reports of the Matthew J. Ryan Veterinary Hospital at the University of Pennsylvania for January 1991 through August 2007 were searched to identify cats that underwent necropsy during this period. The tympanic bullae and middle ears were examined in all cats that underwent necropsy during the time of the study. Cats were included in the study if a diagnosis of middle ear disease had been made on the basis of necropsy findings and if the medical record contained information on the initial complaint for which the cat had been brought to the hospital and the results of a complete physical examination. Cats were excluded from the study if the medical record lacked information related to the aural system, respiratory tract, or nervous system. In addition, cats were excluded if the necropsy had been performed for an outside institution, the cat was a research animal, or a diagnosis of an inflammatory polyp or neoplastic middle ear disease had been made.
Medical records review—Information obtained from the medical records of cats included in the study consisted of signalment, initial complaint, and whether there was any history of otic or airway disease or clinical signs of middle or external ear disease or upper respiratory tract disease. Information obtained from the necropsy reports of cats included in the study included any descriptions of middle ear or respiratory tract disease, the cause of death, any concurrent diseases, and results of any additional testing related to middle ear disease (eg, results of bacterial culture and histologic examination).
In cats with middle ear disease, the condition was classified as suppurative, hemorrhagic, or not described on the basis of findings in the necropsy report. Cats were considered to have suppurative middle ear disease if fluid in the middle ear was described as white, yellow, or green. Cats were considered to have hemorrhagic middle ear disease if fluid in the middle ear was described as bloody or serosanguinous.
Cats were considered to have clinical signs of middle ear disease if they were reported to have unilateral peripheral vestibular disease without motor deficits, Horner syndrome, or facial nerve paralysis. For purposes of the present study, unilateral peripheral vestibular disease was considered to be a sign of middle ear disease because even though this condition is technically caused by internal ear disease, the causative internal ear disease in cats with unilateral peripheral vestibular disease is most often a result of extension of middle ear disease.
Nonspecific clinical signs that could be related to middle or external ear disease (eg, pain, otic discharge, shaking the head, and pawing or rubbing at the ear) were also recorded. Clinical signs of upper respiratory tract disease that were recorded included stertor, nasal discharge, and ocular discharge.
Results
During the 16-year study period, 3,467 cats underwent necropsy at the Veterinary Hospital at the University of Pennsylvania, and unilateral or bilateral nonneoplastic middle ear disease was diagnosed in 84. However, 25 of the 84 cats with nonneoplastic middle ear disease were excluded from the study because they were research animals (n = 9), the necropsy was performed for an outside institution (8), a complete medical record was not available (7), or results of histologic examination of a soft tissue mass within the middle ear were unavailable (1). When these 25 cases were excluded both from the total number of necropsies performed and the number of cats with nonneoplastic disease, the prevalence of nonneoplastic middle ear disease in cats undergoing necropsy during the study period was 1.7% (59/3,442).
For the 59 cats with nonneoplastic middle ear disease, mean ± SD age at the time of necropsy was 8.3 ± 5.6 years (range, 4 weeks to 19 years). There were 24 castrated males, 22 spayed females, 7 sexually intact males, and 6 sexually intact females. Forty-six of the cats were domestic shorthairs, and 4 were domestic longhairs. In addition, there were 2 Maine Coons, 2 Tonkinese, a Siamese, a Russian Blue, a Devon Rex, and an Angora. Breed of the remaining cat was not recorded.
Of the 59 cats with middle ear disease, 26 had bilateral disease and 33 had unilateral disease. Fluid or caseous material was identified in the tympanic bulla in all affected ears. Forty-seven cats (68 ears) had suppurative middle ear disease (ie, yellow, green, or white fluid in the tympanic bulla), and 5 (6 ears) had hemorrhagic middle ear disease. In the remaining 7 cats (11 ears), type of middle ear disease could not be classified. Seventeen cats, including 6 of the cats with bilateral middle ear disease, had evidence of external ear disease.
Twenty cats had been euthanatized because of a poor prognosis related to a primary disease process unrelated to middle ear disease, 14 had been euthanatized for unknown reasons, 11 had been euthanatized because of a failure to respond to treatment for a primary disease process unrelated to middle ear disease, 6 had been euthanatized because of financial reasons, and 8 had died. Necropsy diagnoses included lymphoma (n = 10), cardiac disease (8), renal disease (7), feline infectious peritonitis (5), pneumonia (5), trauma (4), bacterial valvular endocarditis (2), necrotizing enteritis associated with panleukopenia (2), pulmonary carcinoma (2), and necrotizing pyogranulomatous mural ileitis, cerebrocortical necrosis, pyothorax caused by Bacteroides spp, necrotizing enteropathy and septicemia, necrohemorrhagic colitis, systemic toxoplasmosis, necrotizing myocarditis, chylothorax, urethral obstruction, ileal perforation, meningitis, transitional cell carcinoma of the bladder, squamous cell carcinoma of the maxilla, and round cell neoplasia of the liver (1 each).
Results of histologic examination of the tympanic bulla were available for 4 cats. Findings included severe subacute suppurative otitis media, moderate multifocal lymphofollicular and plasmacytic erosive otitis media, mild multifocal chronic lymphocytic otitis media, and severe chronic necrosuppurative and erosive otitis media with abundant intraluminal necrotic cellular debris. Samples from 6 ears were submitted for aerobic bacterial culture. Five of the 6 samples yielded multiple organisms. Escherichia coli was isolated from all 6 ears, Enterobacter spp and Enterococcus spp were isolated from 3 ears each, E-hemolytic Streptococcus spp were isolated from 2 ears, and Clostridium spp and Proteus spp were isolated from 1 ear each.
Fifty-three of the 59 (90%) cats did not have any clinical signs of middle ear disease, whereas 6 (10%) cats did, including 1 cat with bilateral disease. Of the 6 affected cats, 5 had signs of unilateral peripheral vestibular disease, and 1 had Horner syndrome. Eleven cats, including 3 with bilateral middle ear disease, had some evidence of upper respiratory tract disease. Of these 11 cats, 7 had clinical signs of respiratory tract disease and compatible postmortem abnormalities, 2 only had clinical signs of respiratory tract disease, and 2 only had postmortem abnormalities consistent with upper respiratory tract disease.
Discussion
Results of the present study suggested that nonneoplastic middle ear disease was uncommon in cats undergoing necropsy at the Veterinary Hospital at the University of Pennsylvania between 1991 and 2007, with only 59 of 3,442 (1.7%) cats that underwent necropsy during this period being affected. In addition, most (53/59 [90%]) cats with nonneoplastic middle ear disease did not have clinical signs.
The prevalence of nonneoplastic middle ear disease among cats that underwent a necropsy in the present study was lower than the prevalence (6%) reported in a study1 involving 66 randomly selected cats that underwent necropsy for reasons unrelated to middle ear disease. It was also lower than the percentage of cats with sinonasal disease that reportedly had computed tomographic evidence of subclinical bulla effusion (28%).2 Subjectively, our impression has been that for research cats housed at the University of Pennsylvania, the prevalence of middle ear disease at necropsy is higher among cats with upper respiratory tract disease than among cats without. However, our findings should be interpreted with caution because the population in the present study was likely different from the population that would be seen in a general small animal practice. Cats in the present study had been examined at a referral veterinary hospital, and most died or were euthanatized for reasons unrelated to middle ear disease.
Importantly, only 6 of 59 (10%) cats in the present study had clinical signs of middle ear disease. Interestingly, only 30% of cats with bulla effusion in a previous study2 had clinical signs of ear disease. It is possible that clinical signs of middle ear disease were overlooked in some cats in the present study because of the severity of signs associated with the primary disease process. Alternatively, clinical signs may have been subtle or the middle ear disease may have been too mild to cause clinical signs.
The cause of middle ear disease in cats in the present study was often unclear. Eleven cats in this study had evidence of upper respiratory tract disease, and 17 cats had evidence of external ear disease. The link between middle ear disease and upper respiratory tract disease appears to be auditory tube dysfunction, in that experimental obstruction of the auditory tube in cats results in middle ear effusion.3 A decrease in middle ear ciliary area, impaired secretion clearance, and ascending bacterial infection contribute to infectious middle ear disease.2,3 Sixteen animals in the present study had an infectious or necrotizing process unrelated to the ears. Hematogenous spread of infection to the middle ear is cited as a possible cause of middle ear disease in cats,4 although unequivocal evidence of this mode of middle ear infection is lacking.
Results of the present study indicated that although uncommon, middle ear disease may be an incidental finding during diagnostic imaging of cats, even when the cats do not have any clinical signs. Similarly, in a recent study5 comparing results of radiographic, ultrasonographic, and computed tomographic evaluation of the middle ear, 5 of 84 (6%) cats had to be excluded as controls because they had evidence of fluid in the tympanic bulla.
References
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