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.     

Pull-through technique for vertical canal ablation for the treatment of otitis externa in dogs and cats

An alternative technique to ablate the vertical segment of the external auditory meatus, applicable to dogs and cats, is described. The results of this surgery in 11 dogs and one cat are compared with those in seven dogs using the traditional ablation procedure.     

The bacteriological and clinical assessment of a new preparation for the treatment of otitis externa in dogs and cats

The efficacy of a preparation (Oterna—Glaxo Laboratories Ltd) for use in the treatment of otitis externa in small animals has been assessed bacteriologically. The aetiology of the disease was studied in 133 ears of cats and dogs; normal ears were examined by comparison. Pityrosporum canis and staphylococci were the organisms most commonly isolated; their incidence was much higher in clinically affected ears than in normal ears. Gram-negative organisms were found only in diseased ears. Seventy-three clinical cases of otitis in dogs and cats were treated with a preparation containing neomycin, monosulfiram and betamethasone. Bacteriological and clinical evaluations were made before and after treatment and the organisms isolated were tested for sensitivity to the antimicrobial constituents of the preparation. There was a 92 % correlation between the bacteriological and clinical results. A ‘good’ or ‘very good’ bacteriological response was recorded for 71% of the ears treated. Résumé. On a évalué bactériologiquement l'efficacité d'une préparation (Oterna—Glaxo Laboratories Ltd) pour l'usage dans le traitement de l'otite externe de petits animaux. L'étiologie de la maladie a été étudiée dans 133 oreilles de chats et chiens; des oreilles normales ont été examinées pour comparaison. Le Pityrosporum canis et des staphylocoques ont été les microorganismes le plus souvent isolés; leur incidence était beaucoup plus élevée dans les oreilles affectées cliniquement que dans les oreilles normales. Des micro-organisms Gram-négatifs ont été seulement trouvés dans les oreilles malades. Soixante-treize cas cliniques d'otite chez les chats et les chiens ont été traités avec une préparation contenant de la néomycine, du monosulfiram et du bétaméthazone. Les évaluations bactériologique et clinique ont été faites avant et après le traitement et les micro-organismes isolés ont été vérifiés pour la sensibilité aux constituants antimicrobiens de la préparation. Il y avait une corrélation de 92% entre les résultats bactériologiques et cliniques. On a enregistré une réaction bactériologique ‘bonne’ ou ‘très bonne’ dans 71% des oreilles traitées. Zusammenfassung. Die Wirksamkeit eines Präparats (Oterna—Glaxo Laboratories Ltd) für die Behandlung von äußerer Otitis bei kleinen Tieren ist bakteriologisch bestimmt worden. Die Ursachenforschung dieser Krankheit wurde an 133 Ohren von Katzen und Hunden durch-geführt. Zum Vergleich wurden normale Ohren untersucht. Pityrosporum canis und Staphylokokken waren die am häufigsten abgesonderten Lebewesen. Ihr Vorkommen war bei klinisch betroffenen Ohren viel größer als bei normalen Ohren. Gram-negative Lebewesen wurden nur in kranken Ohren vorgefunden. Dreiundsiebenzig klinische Fälle von Otitis bei Hunden und Katzen wurden mit einem Präparat behandelt, das Neomycin, Monosulfiram und Betamethasone enthielt. Bakteriologische und klinische Bewertungen wurden vor und nach Behandlung durchgeführt, und die abgesonderten Lebewesen wurden auf Empfindlichkeit gegen mikrobenbetreffende Bestandteile des Präparates geprüft. Zwischen den bakteriologischen und klinischen Ergebnissen bestand eine 92 prozentige Wechselbeziehung. Eine “gute” oder “sehr gute” bakteriologische Reaktion wurde an 71% der behandelten Ohren festgestellt.     

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.     

Diagnosis and treatment of otitis media in dogs and cats.

Otitis externa/media is commonly found in dogs with chronic ear diseases and in cats with upper respiratory disease and polyps. Diagnosis of otitis media requires attention to history and clinical signs, but it also requires other methods of determining disease within the bulla. If the integrity of the eardrum cannot be determined, assume that there is middle ear disease and proceed accordingly. It is prudent to take necessary precautions to avoid the use of potentially ototoxic ear cleaners or topical medications in suspected otitis media cases. Therapeutic success is possible using systemic and topical treatment within the cleaned bulla. Referral to a dermatology specialist or a radiologist for a CT scan may be indicated in some refractory cases. Surgical intervention may be required to cure these difficult cases.     

Long-term evaluation of the pull-through technique for vertical canal ablation for the treatment of otitis externa in dogs and cats

Between January 1985 and May 1987 53 ears of 35 dogs and five cats with chronic otitis externa were operated on using the pull-through technique for vertical canal ablation. Their postoperative follow-up is analysed, evaluated and described in detail.     

Proliferative and necrotizing otitis externa in four cats

Proliferative and necrotizing feline otitis externa is a rare disorder of unknown aetiology. This condition was diagnosed by skin biopsy in three adult domestic shorthair cats (3-5 years old) and one kitten (6 months old). The affected cats had large tan to dark brown-black coalescing plaques covering the concave surface of the pinnae and external ear canals. Friable material from the plaques and a thick exudate occluded the ear canals. The cats had a secondary bacterial and/or yeast otitis. Prior to the histopathological diagnosis, all cats received numerous otic preparations as well as oral antibiotics and corticosteroids without resolution. Histologically, all cases had strikingly similar changes; acanthosis with pronounced hair follicle outer root sheath hyperplasia and neutrophilic luminal folliculitis, follicular keratosis and individually necrotic keratinocytes in the outer root sheath of hair follicles. One case was documented via skin biopsy to have persisted for 4 years. The adult cats were treated with topical 0.1% tacrolimus and all showed marked improvement although one cat was lost to follow up. The lesions completely resolved with topical tacrolimus alone in one cat and topical tacrolimus in addition to oral prednisolone in another cat.     

Bacteriology and mycology of otitis externa in dogs]

The bacterial and fungal flora of 1118 ears of dogs with otitis externa and 100 ears of healthy control dogs were studied in order to isolate the causative agents. The yeast Malassezia pachydermatis (56%) was by far the most common organism in otitic dogs followed by the bacteria Staphylococcus intermedius (23%), Pseudomonas aeruginosa (12%), Proteus spp. (6%) and Streptococcus canis (5%). A statistical analysis of observed results showed that the incidence of these organisms is significant in otitic dogs. Many strains of S.intermedius, P.aeruginosa and Proteus spp. are resistant to antimicrobial agents commonly used to treat otitis externa. Therefore an antimicrobial susceptibility testing was performed using "Cobas Bact" for these bacterias. Furthermore, 80 strains of M.pachydermatis were submitted to identification-kits (API 20 CAUX, API STAPH, Cobas Micro). The observed results showed that an identification with these tests was not possible.     

Evaluation of the patient with otitis externa

This article considers the history, physical examination, cytologic evaluation of smears and fungal and bacterial culture and sensitivity testing, clinical interpretation of information obtained from a biopsy of the external ear canal, and ancillary aids for the evaluation of the patient with otitis externa.     

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.     

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.     

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.     

Medical therapy of otitis externa and otitis media.

Medical regimens for the successful treatment of infectious otitis may vary widely depending on the degree of pathologic changes of the external ear canals, the status of the tympanic membranes, and the specific microorganisms involved. Chronic otitis media is especially problematic, because impaction of the bullae can be difficult to resolve and these cases often involve antibiotic-resistant bacterial organisms. In fact, the continuing emergence of resistant Pseudomonas spp and Staphylococcus spp will ensure that the medical therapy of otitis remains a dynamic art for the foreseeable future. This article considers the specific antimicrobial agents available for otic use, their potential toxicities, and guidelines for their use.     

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.     

A clinical trial of a topical preparation of miconazole, polymyxin and prednisolone in the treatment of otitis externa in dogs

A topical preparation containing miconazole, polymyxin and prednisolone was shown to be more effective in the treatment of otitis externa in 167 dogs than 2 other ear preparations containing antibiotics, an antimycotic and a corticosteroid. With miconazole, polymyxin and prednisolone, the recurrence rate was 26.7% compared with 72.6% and 54.3% when the other products were used. The mean duration of treatment required to achieve resolution of clinical signs was 9.6 days, compared with 12.2 days and 13.0 days and no cases failed to respond to treatment, compared with 17.7% and 14.3%. Malassezia canis alone (71%) or in association with bacteria (18%) was recovered from 44 of 49 ears cultured.     

Identification and antimicrobial susceptibility patterns of bacteria causing otitis externa in dogs

Bacterial agents are considered important pathogens causing external otitis in dogs. It is essential to carry out bacterial culture and antimicrobial susceptibility test in the case of otitis externa, particularly for chronic or recurring cases. Sterile swab samples were obtained from terminal part of vertical ear canals of 74 dogs with otitis externa for cytology, bacterial culture and antimicrobial susceptibility test. Cytologic smears were stained using Gram and Giemsa staining methods. Aerobic bacterial culture performed on blood agar and MacConkey agar. Among total number of 92 isolated bacteria, 68 were Staphylococcus intermedius. Other isolated bacteria included: Pseudomonas aeruginosa, Proteus mirabilis, Escherichia coli, Pasteurella canis, and six other species of coagulase-negative Staphylococcus. Antimicrobial susceptibility test were performed for all isolated bacteria using 14 antibiotics. Based on the results of this study, all isolated Staphylococcus spp. were sensitive to amikacin, enrofloxacin, and rifampin, and had low resistance to gentamicin, cephalothin and ceftriaxone. More than half of gram-positive isolates were resistant to penicillin and ampicillin. Generally, all isolated gram-negative bacteria, were sensitive to amikacin and enrofloxacin, and had low resistance to ceftriaxone and gentamicin. They were highly resistant to penicillin, eythromycin, and cephalothin. Regarding the results of this study, in cases of uncomplicated otitis externa, it is possible to select antimicrobial drugs merely based on cytology, but it is recommended to perform bacterial culture and antimicrobial susceptibility test. However, in complicated or refractory cases, antimicrobials should be selected based on bacterial culture and antimicrobial susceptibility test.