Computed tomographic features of clinical and subclinical middle ear disease in domestic rabbits (Oryctolagus cuniculus): 88 cases (2007–2014)

• Autores: Ricardo de Matos
• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 246, Nº. 3, 2015, págs. 336-343
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • Objective—To describe and compare CT abnormalities of the middle ear in rabbits (Oryctolagus cuniculus) that had clinical or subclinical middle ear disease and to determine the prevalence of otitis media and evaluate the role of predisposing factors for otitis media in that species.

    Design—Retrospective case series.

    Animals—88 domestic rabbits.

    Procedures—Medical records for rabbits that underwent CT of the head in June 2007 through February 2014 were searched and classified on the basis of reason for head CT (ie, ear-related disease vs non–ear-related disease). The ears, upper respiratory tract, teeth, and other important structures of each rabbit's head were evaluated. Follow-up information was obtained for rabbits with CT abnormalities of the middle ear without clinical signs (ie, subclinical disease).

    Results—12 of 21 (57%) rabbits with clinical signs of ear disease and 18 of 67 (27%) rabbits without clinical signs of ear disease had CT abnormalities of the middle ear. In CT images, all affected ears had soft tissue–attenuating material within the tympanic bulla. Tympanic bulla lysis was associated with clinical middle ear disease. Most (12/18) rabbits with subclinical middle ear disease remained subclinical after CT examination. Middle ear CT-detected changes and lop-ear conformation or otitis externa were strongly correlated; middle ear disease and upper respiratory tract disease were not correlated.

    Conclusions and Clinical Relevance—Data suggested that subclinical otitis media frequently affects rabbits, and those with bulla lysis should be closely monitored. Lop-eared rabbits and rabbits with otitis externa had a higher risk of developing otitis media.

    Otitis media, or inflammatory disease of the middle ear, in rabbits is commonly reported.1–3 Otitis media can be difficult to diagnose in live rabbits because those with otitis media are often subclinically affected unless the disease is associated with otitis externa or interna.1,3–7 Postmortem studies1,4 investigating subclinical otitis media in rabbits have indicated prevalences ranging from 11.5%8 to 32%. With otitis interna, rabbits develop signs of vestibular disease.4,9–12 Reports vary with respect to the prevalence of otitis media in rabbits with vestibular disease: 5.5% in a postmortem study13 of rabbits with neurologic disease, 24% in an Encephalitozoon cuniculi seroprevalence study,14 and 63% in a postmortem study12 of rabbits with vestibular disease. Most of these studies determined prevalence of subclinical and clinical middle ear disease in rabbits at necropsy, not on an antemortem basis, and in meat rabbits or research rabbits, not in domestic rabbits.

    Examination of the external ear canal and tympanic membrane has been proposed for diagnosis of subclinical otitis media. However, neither an apparently normal tympanic membrane nor an apparently normal external ear canal excludes the presence of otitis media.1,4,15 In addition, examination of the tympanic membrane can be challenging, especially in rabbits with otitis externa and in lop-eared rabbits.6,16 Early diagnosis of otitis media is extremely important because infection can spread to the inner ear (causing vestibular disease due to labyrinthitis) or through the internal acoustic meatus and along the vestibulocochlear nerve to the brain (resulting in severe neurologic signs due to encephalomyelitis).4,9–13 Rabbits with otitis interna develop clinical signs of peripheral vestibular disease, including head tilt, nystagmus, ataxia, or rolling.2 Facial nerve paralysis and Horner's syndrome can also develop with otitis media or interna in rabbits.2 Otogenic intracranial infection in humans17 and in dogs and cats18 is reported to be rare. However, it is relatively common in rabbits, affecting up to 50% of rabbits with otitis media.12,13 In those cases, clinical signs of central vestibular disease may be preceded by signs of peripheral vestibular disease, making distinction between central and peripheral vestibular diseases difficult.10,18 The main differential diagnosis for rabbits with central vestibular signs is E cuniculi infection.10–13 Even though serologic tests are available for anti–Pasteurella multocida and anti–E cuniculi antibodies, positive results of assays for serum antibodies reflect exposure and do not correlate with active disease caused by either organism.10,11,13 Owing to the often subclinical signs of otitis media, the difficulty in differentiating otitis media or interna from central vestibular disease, and the relatively high prevalence of otogenic intracranial infection, diagnostic imaging is important for evaluation of the middle ear and early identification of middle ear disease in rabbits. Computed tomography allows cross-sectional evaluation of the entire head, including teeth and upper respiratory tract, without superimposition of structures.19–24 Computed tomography is reported to be more sensitive than, and as specific as, radiography for diagnosing and characterizing the severity of middle ear disease in dogs.25 Computed tomographic findings of otitis media in dogs and cats include thickening, irregularity, proliferation, or lysis of the tympanic bulla wall. In addition, a fluid or soft tissue density may be evident within the lumen of the bulla.19,20,26 The use of CT for diagnosis of otitis media in rabbits has been described in the veterinary medical literature.6,7,11,24,27,28 However, the information is descriptive and limited to CT-detected changes in clinical cases of otitis media.

    In rabbits with otitis media, the primary infection is believed to be a result of bacteria within the nasopharynx that reach the middle ear via the auditory tube.1,4,10 This pathogenesis is supported by the fact that most infections are caused by P multocida, a respiratory tract pathogen.1,3,4,8,9,11,12,29 In addition, high prevalences of middle ear disease in rabbits with concurrent upper respiratory tract infections have been reported (78%4 and 85%8). Otitis media also develops secondary to bacterial or parasitic otitis externa.1,15,30,31 Otitis externa develops more commonly in lop-eared rabbits, possibly because of abnormal conformation of the external ear canal.15 The purpose of the study reported here was to describe and compare CT abnormalities in the middle ear of domestic rabbits (Oryctolagus cuniculus) that had clinical middle ear disease with those in rabbits without signs of disease (subclinical disease) and to determine the prevalence of otitis media in that species. Because there are multiple possible causes of otitis media in rabbits that are not fully understood, another aim was to evaluate the frequency of proposed predisposing factors of otitis media (upper respiratory tract disease, otitis externa, and lop-ear conformation) in rabbits with subclinical or clinical otitis media and in rabbits with or without otitis media. We hypothesized that CT signs of otitis media are a common finding in rabbits that undergo head CT for reasons other than ear disease, that CT middle ear abnormalities would differ between rabbits with clinical and subclinical otitis media, and that predisposing factors to otitis media would be detected more commonly in rabbits with clinical and subclinical otitis media than in rabbits without otitis media.