Diagnosis and medical treatment of otitis externa in dogs and cats

A review of otitis externa in dogs and cats is presented. Aetiology, includes primary causes: ectoparasitoses, allergic diseases, endocrine disorders, pyodermas, trauma and irritation, contact dermatitis, auto-immune skin diseases, drug eruption, keratoseborrhoeic skin disease, tumours and pseudoneoplastic lesions, as well as secondary causes: bacteria and yeasts. Clinical aspects are variable but a practical classification distinguishes two forms: erythematoceruminous otitis externa and suppurative otitis externa. Diagnosis is made in five steps which are clinical examination, direct examination of cerumen (erythematoceruminous otitis externa) or bacterial culture and sensitivity testing (suppurative otitis externa), direct impression smears, cleaning and otoscopy, and diagnosis of underlying skin disease. Medical therapy includes cleaning of the external ear canal and local therapy (acaricides, antifungal agents, antibiotics, corticosteroids, other topical agents, the appropriate selection of an optic preparation being essential). Treatment of underlying skin disease is always necessary. Otitis externa is in fact a dermatological disease complex (like pododermatitis). Although local secondary infections (bacterial and fungal) must be managed in every case, there are grounds for including otitis externa in a larger frame.     

Ulcerative otitis externa responsive to immunosuppressive therapy in two dogs

Two middle-aged dogs were presented with bilateral severe ulcerative otitis externa without previous history of disease or evidence of other skin disease. Based on the exclusion of microbial infection and other primary causes, histopathological findings and response to immunomodulatory treatment, a diagnosis of presumed immune-mediated ulcerative otitis externa was made in both cases. However, the two cases differed with regard to their histopathological characteristics and the course of the disease. This report indicates that primary ulcerative disease needs to be considered in cases of ulcerative otitis externa which are unresponsive to appropriate antimicrobial therapy.     

The pathology of the external ear canal in dogs and cats

A survey of factors which predispose the canine ear to otitis externa is presented. In resected ear specimens of 106 dogs, otitis externa without tumour was found on 58 occasions. In 46 dogs tumours were diagnosed in 15 cases with an otitis externa. In two dogs an inflammatory polyp was found. In the resected ear specimens of 48 cats, otitis externa was diagnosed 27 times, in 6 cases combined with an inflammatory polyp. In 21 cases neoplasia was present. The otitis externa was mainly a chronic proliferative inflammation characterised by hyperkeratinization, hyperplasia of the sebaceous and ceruminous glands, fibrosis and infiltration with plasma cells, lymphocytes and macrophages, often containing ceroid pigment.     

The role of Pityrosporum pachydermatis in otitis externa of dogs: evaluation of a treatment with miconazole.

The bacterial and mycotic flora were assessed in 158 ears of dogs with otitis externa and in 101 ears of healthy control dogs. Pityrosporum pachydermatis occurred in 57 per cent of ears with otitis externa and in 17 per cent of clinically healthy ears. Staphylococci and Pseudomonas aeruginosa were the predominant bacteria in otitic ears, micrococci and Bacillus spp were the most frequent isolates from clinically healthy ears. P pachydermatis, Ps aeruginosa and Candida tropicalis occurred in monoculture in a significant number of mainly chronic cases of otitis externa. A combination preparation, containing miconazole, polymyzin B and prednisolone, was highly effective in controlling the clinical signs of otitis externa and eliminating flora from the affected ears. The data presented suggest that yeasts, and especially P pachydermatis, may be significant pathogens in otitis externa and that antimycotic treatment is an essential part of the treatment of otitis externa in dogs.     

Measurement of body temperature by use of auricular thermometers versus rectal thermometers in dogs with otitis externa

OBJECTIVE: To compare measurements of body temperature obtained with auricular thermometers versus rectal thermometers in dogs with otitis externa. DESIGN: Prospective study. ANIMALS: 100 client-owned dogs: 50 with and 50 without clinical evidence of otitis externa. PROCEDURE: Dogs were evaluated for the presence of otitis externa on the basis of clinical signs, otoscopic examination, and cytologic evaluation of ear exudate. Auricular and rectal temperatures were obtained simultaneously in all dogs prior to and following ear examination. RESULTS: There was a high correlation between auricular and rectal temperatures in dogs with otitis externa both prior to and after ear manipulation. Significant differences were not detected in temperature measurements among dogs with different degrees of otitis externa. CONCLUSIONS AND CLINICAL RELEVANCE: Auricular temperature readings obtained by use of an auricular thermometer in dogs with otitis externa are accurate measurements of body temperature, compared with rectal temperature measurements. Temperature measurements are reliable before and after examination of the ear canal.     

The pathology of the external ear canal in dogs and cats

Summary

A survey of factors which predispose the canine ear to otitis externa is presented In restected ear specimens of 106 dogs, otitis externa without tumour was found on 58 occasions. In 46 dogs tumours were diagnosed in 15 cases with an ototis externa. In two dogs an inflammatory polyp was found.

In the resected ear specimens of 48 cats, otitis externa was diagnosed 27 times, in 6 cases combined with an inflammatory polyp. In 21 cases neoplasia was present.

The otitis externa was mainly a chronic proliferative inflammation characterised by hyperkeratinisation, hyperplasia of the sebaceous and ceruminous glands, fibrosis and infiltration with plasma cells, lymphocytes and macrophages, often containing ceroid pigment.     

Mechanisms of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from canine infections

Chronic otitis externa in dogs is often associated with Pseudomonas aeruginosa infection. Fluoroquinolones are often used for treating such infections. Fluoroquinolone resistance mechanisms were characterized in 10 strains of P. aeruginosa isolated from chronic canine otitis externa. Nine out of ten strains harbored a mutation in the gyrA gene and presented an overexpression of efflux pump(s). There was a good correlation between the lipophilicity of the fluoroquinolone being tested and the effect of the efflux pump inhibitor in the final MIC. Therefore, both mechanisms, mutation in the gyrA gene and increased efflux pump(s), seem to play an important role in the acquisition of fluoroquinolone resistance in veterinary clinical isolates of P. aeruginosa. Levels of resistance to fluoroquinolones suggest that they could not be a good choice for systemic therapy of Pseudomonas otitis.     

Surgical Management of Rabbit Ear Disease

Clinical signs associated with otic disease in rabbits (Oryctolagus cuniculus) are very similar to those demonstrated in dogs and cats. The surgical treatment options to resolve diseases involving the rabbit ear are also comparable with those used for canine and feline species. However, there are key anatomic and physiologic differences that must be accounted for to perform proper surgical treatment on a rabbit that has been diagnosed with ear disease. This article describes the diagnostic and treatment options for otitis externa, otitis media, and otitis interna, with an emphasis on surgical procedures and the important distinctive otic features of the rabbit patient. The ventral bulla osteotomy procedure is recommended for management of otitis media in rabbits without otitis externa. In rabbits with pathology in the external ear canal and the middle ear, total ear canal ablation and lateral bulla osteotomy should be performed. This combined procedure will allow the surgeon to address pathology in both sites, with the ultimate goal of resolution of the underlying disease etiology. Lateral ear canal resection is only appropriate in rabbits with otitis externa without otitis media; however, this surgical procedure may not resolve the otitis externa. If this is a concern, a total ear canal ablation should be done because it offers a greater chance of success.     

A review of techniques for the investigation of otitis externa and otitis media

Otitis externa, inflammation of the externa ear canal, is relatively easy to diagnose based on the history and physical examination findings. The diagnosis of otitis media, inflammation of the middle ear cavity, is more challenging, with the work-up being both costly and, at times, invasive. The pathogenesis of otitis externa has been classified into predisposing, primary, and perpetuating factors. It is critical to the management of ear disease that the clinician recognize and investigate which factors are contributing to each individual patient's ear disease. Failure to identify and address the primary and/or predisposing factors is the most common cause of chronic recurrent otitis externa. Chronic inflammation of the ear canal leads to the development of the perpetuating factors, which may be the major reason for treatment failure, regardless of the primary cause of the ear disease. In this article, the predisposing, primary, and perpetuating factors involved in ear disease will be presented, along with a review of the techniques used in the diagnosis of otitis externa and otitis media.     

Efficacy of a pimaricin suspension for treating otitis externa associated with M pachydermatis

A clinical trial was conducted to evaluate the efficacy of a 1 per cent pimaricin suspension in the treatment of canine otitis externa associated with Malassezia pachydermatis. Of 40 dogs examined, M pachydermatis was the sole infection in five ears and was commensal with other organisms in 35 ears. Pimaricin in a 1 per cent suspension was administered twice a day for two weeks. Employing continuous therapy, signs accompanying otitis externa were ameliorated steadily, and satisfactory results were achieved in 33 of the dogs. No noticeable side effects were observed with the pimaricin suspension.     

Evaluation of an ear cleanser for the treatment of infectious otitis externa in dogs

Thirty-one ears (16 dogs) with otitis externa originating from bacterial or yeast infections were enrolled in a study to evaluate the in vivo efficacy of an ear cleanser containing 2.5% lactic acid and 0.1% salicylic acid for the treatment of infectious otitis externa. The affected ears were treated with the ear cleanser twice daily for 2 weeks and evaluated after 1 and 2 weeks of treatment. The ear cleanser was effective in resolution of infection in 67.7% of the ears, and clinical signs of infectious otitis externa were significantly reduced within 2 weeks.     

Morphologic measurements of the external horizontal ear canal of dogs

Microscopic anatomy of the horizontal part of the external ear canal was evaluated in 24 dogs. Sixteen dogs were from breeds known to have a predisposition to otitis externa. The remaining 8 dogs were from breeds that do not have a predisposition to otitis externa. Dogs were separated into groups according to predisposition to otitis externa: group 1-predisposed dogs without otic inflammation, group 2-predisposed dogs with otic inflammation, and group 3-nonpredisposed dogs without otic inflammation. Qualitative microscopic evaluation of distribution of hair follicles revealed hair within proximal, middle, and distal regions of the horizontal ear canal in all breeds. The degree of keratinization was directly proportional to the presence of otic inflammation and was excessive in group-2 dogs. Quality of sebaceous glands within the horizontal ear canal was similar among dogs with and without otitis externa, whereas the quantity of apocrine tubular glands was significantly increased (P less than 0.05) in dogs with otitis. Quantity of apocrine tubular glands was also greater in group-1 dogs than in group-3 dogs. Thickness of the soft tissue in the external ear canal increased in direct proportion to the progression of disease and was greatest in the proximal region of the affected ear canal. Soft tissue located caudally between nonopposing ends of the annular cartilage, within the proximal region of the horizontal ear canal, contained few glands and hair follicles in dogs without otitis externa. In dogs with otitis externa, this region was infiltrated by distended apocrine tubular glands.     

Effects of beta-thujaplicin on anti-Malassezia pachydermatis remedy for canine otitis externa

The antifungal activity of beta-thujaplicin was evaluated against 51 Malassezia pachydermatis strains isolated from canine ear canals with or without otitis externa. For comparison, sensitivity tests were performed on M. pachydermatis isolates for nystatin, ketoconazole, and terbinafine HCl, all clinically available antifungal agents. The minimal inhibition concentrations over 50% of the tested isolates (MIC50) were 3.13 microg/ml for beta-thujaplicin and nystatin, 0.016 microg/ml for ketoconazole, and 1.56 microg/ml for terbinafine HCl. The antifungal effect for M. pachydermatis of beta-thujaplicin compared favorably with commercial antifungal agents. None of the 51 M. pachydermatis isolates showed resistance against any of the tested antibiotics investigated in this study. Ten representative isolates of M. pachydermatis were subcultured for 30 generations at concentrations close to the MIC levels of beta-thujaplicin, nystatin, ketoconazole, and terbinafine HCl, and examined to determine whether they had acquired resistance to each drug. As a result, M. pachydermatis was found to achieve resistance more easily for ketoconazole and terbinafine HCl than for beta-thujaplicin or nystatin. The MIC50 of beta-thujaplicin did not change during the course of subculture, and it is thought that the potential development of a resistant strain is low, even with continuous infusion for otitis externa therapy. beta-Thujaplicin is an inexpensive and safe treatment with anti-inflammatory and deodorant effects that can be recommended as an effective remedy for canine otitis externa.     

Diagnosis and medical treatment of otitis externa in the dog and cat

Otitis externa is no longer viewed as an isolated disease of the ear canal, but is a syndrome that is often a reflection of underlying dermatological disease. Causes are classified as predisposing (increase the risk of otitis); primary (directly induce otitis), secondary (contribute to otitis only in an abnormal ear or in conjunction with predisposing factors) and perpetuating (result from inflammation and pathology in ear, prevent resolution of otitis). Common primary causes include foreign bodies, hypersensitivity (particularly atopy and food allergy), keratinisation disorders (most commonly primary idiopathic seborrhoea and hypothyroidism) and earmites, particularly in cats. A systematic diagnostic procedure is required to identify causes and contributing factors. This should include history, clinical examination, otoscopy and cytology in all cases and culture and sensitivity as well as otitis media assessment and biopsy in severe and recurrent cases. Ancillary tests may be required depending on the underlying cause. Treatment consists of identifying and addressing predisposing and primary factors; cleaning the ear canal; topical therapy; systemic therapy where necessary; client education; follow-up; and preventive and maintenance therapy as required.     

Otitis externa induced with Malassezia pachydermatis in dogs and the efficacy of pimaricin.

Eight beagles were experimentally inoculated intraotally with Malassezia pachydermatis to induce acute otitis externa. Three or 4 days after the inoculation, the animals showed the symptoms of otitis externa. All ear canals were erythematous and the dogs were shaking their heads. A large number of M. pachydermatis was noticed in exudate taken from every ear canal. Clinical signs of otitis externa were reduced after treatment with 0.1 ml (per canal) of 1% pimaricin suspension twice a day for 3 days. The amount of exudate decreased gradually and 12 of the 16 ear swabs examined, thereafter, were found to be negative for M. pachydermatis within 10 days. No side effects were observed in all the treated cases. These results suggested that M. pachydermatis could induce the canine otitis externa, and that pimaricin is effective agent for M. pachydermatis infection in ear canals.     

Medical management of otitis externa

Successful medical management of otitis externa requires attention to all of the following points: 1. Diagnose and treat systemic or underlying disease(s). 2. Carefully clean and examine the entire ear canal before starting therapy. This includes removal of foreign bodies, parasites, hair, and other obstructions. 3. Apply carefully chosen topical preparations based on gross and microscopic examination. 4. Educate clients as to the causes of the otitis externa and their role in treating the disease. 5. Schedule regular follow-up examinations until the disease is completely cured. 6. Recommend preventive procedures such as drying ears after swimming, corrective surgery, and so on. 7. Use systemic treatment when indicated by chronicity of disease or the owner's inability to treat the patient.     

Efficacy of boric-complexed zinc and acetic-complexed zinc otic preparations for canine yeast otitis externa

The purpose of this 2-week, double-blinded, controlled clinical trial was to evaluate the efficacy of topical amino acid-complexed zinc gluconate formulated with boric acid (ZGB) or acetic acid (ZGA) versus a topical placebo in the treatment of yeast otitis externa in dogs. Included in the study were dogs with otitis externa and a cytopathological finding of yeast organisms in the affected ear. Ears were treated with the placebo, ZGA, or ZGB medications. Yeast counts as well as clinical appearance of the ears were monitored. Results revealed that ZGB significantly reduced the number of yeast organisms in cases of otitis externa.     

Inflammatory middle ear disease of the dog: the pathology of otitis media

Inflammation within the middle ear cavity was recognised in 62 of the ears of 42 dogs with chronic otitis externa and otitis media, after biopsy or necropsy of the middle ear. The pathological changes in the middle ear resembled those reported in other species or after the experimental induction of otitis media in dogs. Perforations in the tympanic membrane were rarely found; on the contrary, the membrane was often thickened. However, the question of whether a perforation in the tympanic membrane must occur before otitis externa can extend to otitis media was not resolved.     

Causes of otitis externa.

Dogs with long-standing, chronic, recurrent otitis externa often represent one of the most frustrating types of problems in daily clinical practice. The important aspect of this discussion is that the clinician may be presented with a patient in which the primary chief complaint is otitis externa but a wide variety of disease processes may be causing the problem, including various combinations of the primary, predisposing, and perpetuating causes as discussed previously. The use of a thorough history and general and dermatologic physical examinations often leads the clinician to establish a systematic approach to identify the specific underlying problems. Until this is accomplished, the recurrent nature of the otitis externa will remain as a persistent problem.     

Juvenile cellulitis in a puppy

An 8-week-old, male Labrador retriever presented for acute onset of left hind limb lameness. This rapidly progressed to juvenile cellulitis, characterized by dermatitis of the face, otitis externa, regional lymphadenopathy, lethargy, and depression. The puppy made a full recovery on glucocorticoid therapy.