CONCURRENT SESSION PRESENTATIONS OTIC STRUCTURE AND FUNCTION Cole LK The Ohio State University, College of Veterinary Medicine, 601 Vernon Tharp Street, Columbus, Ohio 43210 Otitis refers to inflammation of the ear and may include not only the external ear canal in otitis externa, but may also involve the middle ear in otitis media, and the ear pinnae as well. Otitis externa is the most common ear disease in the dog and cat. The reported incidence is between 10 to 20% in the dog and 2 to 10% in the cat. Otitis externa is one of the most common reasons for animals to be referred to dermatology specialists, and is a very common clinical problem managed by general practitioners as well. It is important to be able to recognize normal otic anatomy to be able to diagnose otic disease. Prior to examination of the animal, it is important to obtain a complete and thorough history from the owner. Even though this can be a time-consuming step, it is invaluable for a complete assessment of the animal and for insight into the primary cause of the otitis. A dermatologic history form can be mailed to the client prior to the appointment, or it can be filled out when the client arrives. Questions include: • Onset of the otitis, unilateral or bilateral • Seasonal, non-seasonal, or seasonally non-seasonal • Current and previous treatment(s) used for the otitis as well as outcome, side effects, drug reactions • Previous steroid administration • Other dermatologic concerns: pruritus, alopecia, “rash” • Current and previous diets and treats • Current treatments for other concurrent diseases or preventive treatments (flea control, heartworm prevention) • Any others in home with skin problems One should also inquire about the clinical signs that prompted the owner to seek veterinary care. Common clinical signs associated with otitis externa include: • Head shaking • Scratching and rubbing the ears • Pinnal alopecia • Excoriations • Odor • Pain • Hearing loss • Behavioral changes The next step is to perform a general examination as well as a dermatologic examination. In some cases, a neurological examination may be needed if one suspects the animal to have concurrent otitis media or otitis interna. If otitis media is present as well, the animal may exhibit neurological signs such as facial nerve paralysis or Horner’s syndrome. However, remember that the most common clinical sign of otitis media is recurrent otitis externa. Head tilting, circling, and nystagmus may indicate otitis interna. EXTERNAL EAR CANAL The external ear is composed of two elastic cartilages: the annular and auricular cartilage. The auricular cartilage expands to form the pinna. The pinna is a mobile structure designed to localize and collect sound waves and transmit them to the tympanic membrane. The auricular cartilage of the pinna becomes funnel shaped at the opening of the external ear canal. The opening of the external ear canal is bounded by the helix (the free, slightly folded margin of cartilage at the base of the pinna) rostrally, the tragus laterally, and the antitragus caudally. The antitragus is a thin, elongated piece of cartilage caudal to the tragus, and separated from it by the intertragic incisure. This anatomical region is the area in which I will insert the otoscopic cone or otoendoscope into the ear canal for the otoscopic examination. The vertical ear canal runs for about 1 inch, extending ventrally and slightly rostrally before taking a medial turn and forming the horizontal ear canal. There is a prominent cartilaginous ridge (“Noxon’s Ridge") that separates the vertical and horizontal ear canals and when the ear is in its normal position, makes otic examination of the horizontal ear canal difficult without elevating this ridge by grasping the ear pinna and lifting the ear. The horizontal ear canal is composed of auricular and annular cartilage. The auricular cartilage rolls as it forms a tube. A separate cartilaginous band, the annular cartilage fits within the base of this tube. The annular cartilage overlaps with the osseous external acoustic meatus and articulates via ligamentous tissue, giving the external ear canal flexibility. In most breeds of dogs, hairs are present in the external ear canal, decreasing in number from distal to proximal. A very few fine hairs are found at the entrance of the cartilaginous external acoustic meatus. I find these hairs are a useful landmark when flushing an ear to locate the tympanic membrane. Cerumen is an emulsion that coats the ear canal. It is composed of desquamated keratinized squamous epithelial cells along with the secretions from the sebaceous and ceruminous glands of the ears. Cerumen from dogs with normal ears contains significantly more lipid than from dogs with otitic ears, although variation may occur in individual dogs. However, in dogs with otitis externa, those with high levels of lipids in their cerumen also had a high incidence of concurrent otic Malassezia pachydermatis. It appears that the overall lipid content and lipid class composition of human and canine cerumen are similar. In humans however, it is thought that cerumen protects the ear canal from invasion of microorganisms and injury and it exhibits bacteriocidal and antifungal activity, which may or may not be true in the dog. The self-cleaning function of the external ear canal is primarily achieved by a process called epithelial migration. The epithelium in the ear canal grows outward from the tympanic membrane toward the opening of the external ear canal. These epithelial cells carry debris with them as well. When the anatomy of the epithelium of the ear canal is altered, or when the rate of epithelial movement is slowed due to age, debris accumulates in the ear canal or on the pars flaccida. This condition is termed “failure of epithelial migration”. Wax and keratin accumulate to form either soft wax plugs or ceruminoliths. Removal of these usually requires the patient to be under general anesthesia or heavily sedated. Soft wax plugs are usually easy to remove by flushing with a ceruminolytic agent and saline. However, ceruminoliths may be more difficult to remove, requiring additional soaking time with a ceruminolytic agent as well as the use of grasping forceps. After the removal of a ceruminolith, the tympanic membrane may appear abnormal, or may even have small tears in it. These small tears heal rapidly. If the tympanic membrane is torn while removing the ceruminolith, it is important to flush the ear with sterile saline to remove the ceruminolytic agent. THE MIDDLE EAR The middle ear consists of an air-filled tympanic cavity, three auditory ossicles, and the tympanic membrane. The tympanic membrane is located at a 45-degree angle in relation to the central axis of the horizontal part of the external ear canal. The tympanic membrane is a semitransparent membrane that separates the external ear canal from the middle ear, is thin in the center and thicker at the periphery, and is divided into two sections, the small upper pars flaccida and the larger lower pars tensa. The pars flaccida is the pink, small, loosely attached region forming the upper quadrant of the tympanic membrane that contains small blood vessels. In most dogs, grossly the pars flaccida is flat, while on occasion, in other dogs, this structure bulges into the external ear canal. This bulging pars flaccida can be present in the ears of normal dogs as well as in ears of dogs with otitis externa. Since no differences can be found histologically between a bulging pars flaccida and a flat pars flaccida, it appears unlikely that there is a structural difference causing the pars flaccida to bulge. There may be increased pressure in the middle ear of dogs with a bulging pars flaccida. In the Cavalier King Charles spaniel, however, it does appear that a bulging pars flaccida is indicative of a middle ear disease, specifically primary secretory otitis media. Primary secretory otitis media (PSOM) or “glue ear” is a disease described almost exclusively in the Cavalier King Charles spaniel (CKCs). Dogs with this condition may exhibit head and neck pain, “air” scratching, neurological signs (facial paralysis, head tilt, vestibular signs), and hearing loss. In a retrospective review of 61 cases of PSOM, the diagnosis was made based on visualization of a bulging opaque tympanic membrane with an operating microscope and the finding of an accumulation of mucus in the middle ear after myringotomy. No additional tests were used to evaluate the dogs for otitis media. The cause of the middle ear effusion is suspected to be due to Eustachian tube dysfunction, similar to children with secretory otitis media (SOM). SOM is one of the most common ear disease in children. Symptoms and signs are often lacking or may be minimal, such as mild hearing loss, which may not be recognized by the parents. In my experience, radiography, specifically computed tomography (CT), is the best diagnostic test for a definitive diagnosis of PSOM. A bulging pars flaccida observed otoscopically in this breed is most likely indicative of PSOM. However, a normal tympanic membrane does not rule out the disease. Other diagnostic tests, such as hearing tests (brain stem auditory evoked responses [BAER]), impedance audiometry (tympanometry, acoustic reflex, pneumotoscopy), and bulla ultrasonography are currently being evaluated in a prospective study to determine their usefulness in the diagnosis of PSOM. Current treatment of PSOM is removal of the mucus via a deep ear flushing of the middle ear. Culture and cytology of the mucoid exudate is usually negative; however, is still recommended. In the above retrospective study, various forms of medical management were used post-flushing, however, a number of CKCs did require repeated middle ear flushes to remove the mucus from the middle ear. This is not necessarily unexpected, since the cause of this disease has yet to be identified.