Dr Andrea Volk
DVM, Dr.med.vet., MVetMed, DipECVD, MRCVS
RCVS and European Specialist in Veterinary Dermatology
You are presented with one of those cases in clinic that make your heart sink. “George” is a 2 and half-year-old male neutered Cocker Spaniel with a history of recurrent otitis going on for a year now and his owner has come in to complain that the itching and smell are back.
As you haven’t seen him before, you flick through his history which reveals that originally the otitis was restricted to the left ear, but in the last few months both ears have been affected. Initial episodes resolved rapidly with Fusidate/Framycetin/Nystatin/Prednisolone or Miconazole/Polymyxin B/Prednisolone ear drops. However, otitis episodes have been becoming both more frequent and more severe. The last few episodes proved refractory to “first line” treatments but did respond partially to a topical combination of gentamicin/clotrimazole/betamethasone. None of the vets who have examined him have detected any signs of ear mite infestation, but there appear to have been relatively few diagnostics done – probably because until recently each episode had resolved with empirical treatment.
Fortunately, George doesn’t seem too bothered by your examination, although he is quite fidgety and clearly uncomfortable around his ears. However, there is a lot of discharge in both ear canals. There are no other abnormalities apparent on your clinical examination and his skin and coat appear otherwise in good condition.
Severe otitis externa. The ear canal is inflamed and swollen shut and ceruminous exudate is present. Image copyright Joel Mills.
How would you describe the current problem?
George’s problem shouldn’t be dismissed as a series of unconnected incidents. Rather, we are dealing with bilateral intermittent otitis that periodically goes into remission, but has never really been resolved.
What are the differential diagnoses in this case?
When dealing with any “ear infection” it is always useful to break down the various contributing factors into Primary, Predisposing and Perpetuating factors.
1) Primary Factors – e.g. Foreign bodies, Otodectes cyanotis infestation, allergic dermatitis, keratinization disorder (‘seborrhoea’), neoplastic changes.
At the moment, we have no idea what the primary cause might be, or whether it is still present. Despite the absence of any other skin problems, after a year of otitis externa it could still be of an allergic origin. In addition, Cocker Spaniels are predisposed to keratinization disorder.
2) Predisposing Factors – ear conformation, water…
Cockers tend to suffer more frequently from otitis externa, having pendulous pinnae, hairy ears, a tendency towards excess cerumen, as well as quite long ear canals. They are also ‘predisposed’ to idiotic behaviour (!) increasing the risk of foreign bodies or waterlogged ear canals, as well as going regularly to the groomer for baths and clips.
Unfortunately, most of the above is not preventable, though swimming can be restricted and the groomer asked to be extra careful to keep the ears dry.
3) Perpetuating Factors
Chronic ear inflammation, regardless of the underlying cause, leads to stenosed ear canals which are more resistant to even best treatment.
Otitis media should also be considered. In this situtation there is a nidus of infected debris in the middle ear, protected from the action of topical antibacterial agents by the tympanic membrane, if intact.
Secondary infections would explain the recurrent pruritus and smell. This may well include a fungal component (most likely Malassezia), but bacterial infection is also possible. However, the exact bacteria we’re dealing with here is not clear. Fusidate (originally used) is effective against gram positive cocci, whereas the framycetin has good activity against gram negatives. It may well be that a resistant Staph or Strep has developed following overuse; which should be followed up with a culture & sensitivity. However, it is equally likely that by exterminating the gram positive flora of the ear canal, a gram negative infection has become established. This would explain the greater success of polymyxin B or gentamicin, which tend to be more effective against gram negative bacteria. Having said that, a concern is development of a Pseudomonas infection, as this bacterium is able to generate resistant isolates relatively quickly, even in the presence of a previously sensitive antibiotic. Interestingly, Polymyxin B often shows in-vitro sensitivity to Pseudomonas, though this is often not the case in-vivo due to concurrent neutrophils.
Owner compliance is also a very important consideration in George’s case. Is treatment actually administered as prescribed? How well is the cleaning of the ears going at home? Does the owner return for rechecks as requested?
Malassezia can be seen on this ear slide (arrows). This image was taken with an iPhone camera directly through the microscope’s eyepiece. Photo copyright Dr Andrea Volk.
So, what do you want to do next?
A key feature in managing any recurrent otitis externa case is ear cytology. In this case, it is essential that we get some idea of what we’re dealing with at the cellular level.
In addition, we ideally need to have a really good look at the ear canal. However, the amount of debris present and stenosis in combination with likely pain in these chronically infected ears, frequently makes otoscopy unrewarding to impossible. Ideally, you’d like to view the tympanic membrane for integrity. If this is not possible due to pain or debris or stenosis, or all of the above, likely systemic treatment needs to be initiated to reduce these factors. And the tympanic membrane will need to be assessed at a later stage. What is important here is the communication with the owner, so that they are aware of the unknown status of the tympanic membrane.
Are there any other considerations you might want to bear in mind?
Otitis externa (with or without otitis media) will impair hearing as air-conduction is reduced to absent depending on its extent. Should otitis media extend to an otitis interna, sensori-neural deafness could even come into the equation.
So how would you proceed?
Stay tuned for Part 2 of this Blog to find out the best ways to tackle tricky ear cases like George!
So if you’ve got any patients with suspicious skin lesions, odorous otitis cases, or generally pruritic patients who are making your heart sink every time you see their names on the consult list… give VVS a call and see what we can do to make your life easier and their lives better!