Otitis Externa with Dr Dani Hoolahan (OVC 2023)

This lecture on the important clinical condition of otitis externa, was presented by specialist veterinary dermatologist, Dr Daneille Hoolahan as part of the 2023 Online Veterinary Conference by Vet Education. This was such an informative lecture, it is hard to condense the takeaway points into short form – but here we go!

Key Points

Definition: Otitis externa is inflammation of the external ear canal epithelium +/- pinnal dermatitis. Otitis externa is reported in up to 20% of dogs, and 6.6% of cats.

Clinical Signs: 

Clinical signs can include some or all of the following:

• Head shaking
• Scratching
• Pain
• Erythema
• Excoriations
• Alopecia
• Exudate
• Odour

Aetiology:

Most cases of otitis externa have multifactorial aetiology, with one or more of the following causes – 

• Abnormal ear canal morphology e.g. excessive hair, narrow ear canal
• Ceruminous gland hyperplasia – esp Cocker Spaniels
• Allergic dermatitis – the most common trigger. Can be atopic dermatitis, food allergy-related dermatitis, contact allergic dermatitis
• Ectoparasites – especially in young cats
• Increased ear canal humidity e.g. bathing, swimming, frequent cleaning etc.
• Foreign body, tumour or polyp in the ear canal
• Immune-mediated disorders

Atopic dermatitis is the most common trigger seen.

• The resulting otitis externa can be unilateral or bilateral. Initially Malassezia is the most common secondary invading organism seen, but as the disease progresses, bacterial infection can also be seen.

Cutaneous adverse food reaction – see these less frequently in dogs and cats.

• See ear inflammation commonly with this condition. Malassezia is common initially, then other bacteria

Contact reaction – eg to an ear cleaner, or drugs (eg neomycin)

• See redness and swelling on pinna and around base of pinna = the so-called ‘drip configuration’ 
• Often just see large numbers of inflammatory cells on swab

Parasites

• look for Otodectes in every cat.
• Demodicosis is more common in cats than in dogs with otitis externa
• Demodex cati may be seen on swabs – in these cases look at CBC, biochemistry, FIV, urinalysis; as initial screen to look for underlying disease/trigger that has allowed Demodex to take hold (eg FIV, diabetes)
• Bravecto or Revolution for treatment

Cornification disturbance

• hypothyroidism or Cushing’s are the most common endocrinopathies seen that trigger changes causing otitis externa. Get changes in glandular secretions, and cerumen is pro-inflammatory.
• Sometimes referred to as “Primary idiopathic seborrhoea”
• Always screen older patients with otitis externa for concurrent endocrinopathy

Neoplasia can trigger inflammation. 

• Tend to be benign in dogs, malignant in cats (if not polyps)

Immune mediated diseases

• pemphigus foliaceus or erythema multiforme most common
• Other causes include SLE, ischemic dermatopathy, juvenile cellulitis

Complicating Factors

There may also be Perpetuating Factors which don’t initiate disease but perpetuate inflammation, including 

• Bacteria
  • usually Staphylococcus & Streptococcus spp
  • also can get Pseudomonas, which is often seen in referral practice -> and which often causes ulceration, especially of external ear canal and pinna
• Fungus/Yeast
  •  Malassezia very common, Candida is much less common, Aspergillus rare, but can see with aural foreign body
• Otitis media
  • see with chronic ear disease. 80% of chronic ears had OM in one study.
  • often have no neurologic signs at all and quite often tympanic membrane is intact
• Chronic change
  • epithelial hyperplasia, glandular hyperplasia
  • calcification of auditory canal; this is bad and usually means the patient will need surgery (total ear canal ablation & bulla osteotomy)
    

Diagnosis of otitis externa

• Otoscopy 
• Cytology 
  • important – do this after initial otoscopy
  • collect sample with a cotton tip from the junction of horizontal and vertical canals.
  •  Tells you what types of organisms are down there today
• Culture and Sensitivity
  • not a first step, as we are not giving antibiotics via blood, but are administering topically onto the bacteria with ear drops – so concentrations of drug in the ear will be much higher than would be in the blood with oral dosing. 
  • Culture is indicated if poor response to several weeks of topical therapy
  • Culture is indicated in otitis ear with only inflammatory cells on cytology, as Pseudomonas is a possibility
• Imaging
  • common in referral practice
  • MRI/CT are preferred
  • Radiographs are not good for diagnosis of otitis media

Treatment of Otitis Externa

Golden Rules:

• topical steroids required in all cases
• often need systemic steroids if there is moderate to severe inflammation and stenosis, or if there is a diagnosis of Pseudomonas
• Choose a topical medication that contains a steroid to match the ear
  • prednisolone for mild inflammation
  • betamethasone or mometasone for increasingly severe inflammation

Allergic Otitis Externa:

• Corticosteroids
• Dexamethasone ophthalmic 0.1%
• Cortavance
• Elocon lotion
• Ear cleaner
  • Ear cleaners 1-2x week and no more than this when treating
  • Maintenance cleaning is done on a weekly to monthly basis

• Epiotic SIS a good cleaner (for both cats and dogs), 
• Otoflush, only tends to use if eardrum ruptured, (lecturer uses this quite a bit in cats, as their ears are more delicate and this is the least irritating of the three cleaners)
• PAW Gentle ear cleaner if have significant ceruminous debris in external ear canal (doesn’t use in cats)
• Topical antibiotics (where indicated)
  • most ear drops are triple therapy
  • Surolan. Otomax. Mometamax (for mild to severe case) 
  • The strength of contained steroids is mild, moderate and strong in these three in order written.
  • Apply once a day, amount given depends on size of the dog/cat 
  • Need to line the entire ear canal. Treat for a minimum of two weeks – ensure dispense enough

Refractory otitis externa

• base antibiotic therapy on culture and sensitivity 
  • Ticarcillin. 
  • Enrofloxacin/dexamethasone solution made in clinic (recipe provided by lecturer via email)
  • Amikacin
  • Tobramycin ophthalmic drops
  • Compounded
    • 1.5% enrofloxacin, 0.1% dexamethasone & 2% ketoconazole
    • 5% ceftazidime, 0.1% dexamethasone +/- terbinafine & itraconazole
  • Apply after ear clean under sedation/GA, then weekly for 4 doses. Good when the owner cannot medicate the ear

Ruptured tympanic membrane

• Antibiotics
  • For bacterial otitis externa/media: 
    • Injectable enrofloxacin + dexamethasone
    • Ciproxin HC poloxamer
• Cleaner
  • Otoflush (especially uses this for bacterial infections), or
  • 2% acetic acid/boric acid, or 
  • 50:50 white table vinegar and sterile saline (mainly for yeast infections)
    

Systemic antibiotics

• not typically given for otitis externa, as they do not penetrate the external ear canal well. 
• Recommended for otitis media though
  • Cocci – cephalexin, clindamycin, Clavulox 
  • Rods – enrofloxacin, marbofloxacin, ciprofloxacin
  • Fungal – ketoconazole, itraconazole, terbinafine etc

Maintenance Plan after Otitis Externa resolved

• Very important

• Regular ear cleaning e.g. Epiotic SIS, Otoflush
  • Weekly to monthly
• Regular anti-inflammatory topically
  • Elocon lotion, Cortavance
  • Flamazine/dexamethasone solution compounded – e.g. if have severe ceruminous gland hyperplasia

Recurrence:

Recurrence is due to 

• failure to identify all causes
• inadequate management – Is the owner able to apply the medication plan?

We need to address treatment failures

Must always do cytology!