Otitis externa Flashcards
Ear physiology
- Temp 38.2–38.4 ˚C
- Humidity 88.5%
- pH 6.1/6.2
- Otitis associated with rise in temp, humidity and pH
- Sebaceous glands
- Ceruminous glands
- Lipids + sloughed keratinocytes form cerumen
– Cerumen traps small FB
– Anti-bacterial/yeast
– Epithelial migration moves wax from TM to the external space
– Epithelial migration disturbed by inflammation, wetness, hyperplasia and physical blockage
Normal flora in ear canal
- Gram +ve cocci predominate (but no growth in some dog’s ears)
- Similar species to those found on the skin
- Micrococcus spp.
- Coagulase negative staphylococci, Staphylococcus schleiferi and Staphylococcus pseudintermedius
- Streptococcus species
- Malassezia and many others
Factors causing microbial overgrowth (or dysbiosis)
- Humidity
- Inflammation (and swelling)
- Reduced epithelial migration
- Epithelial surface changes
Most common organisms causing microbial overgrowth/dysbiosis
- Staphylococcus pseudintermedius
- Malassezia pachydermatis
In treating otitis it is useful to consider PSPP(P)
- Primary disease
– e.g. atopic dermatitis, Otodectes cyanotis - Secondary disease
– e.g. Malassezia, Staphylococci & Pseudomonas spp. - Predisposing factors
– e.g. Hairy &/or pendulous ears, stenosis - Perpetuating factors
– e.g. Ear canal hyperplasia, stenosis and scarring
(-Pain
– Very common
– Difficult to manage in face of steroids
– Results in difficulty in examination, subsequent behavioural problems at the vets
- Needs addressing for animal welfare
Predisposing causes
- Conformation
- Excessive moisture
- Obstructive ear dz
- Primary otitis media
- Treatment effects
Predisposing causes - conformation
- Excessive hair growth in canals (e.g. poodle) (dogs with anagenic hair growth can have excessive hair growth)
- Hairy concave pinna (e.g. cocker spaniel)
- Pendulous pinna (e.g. basset hound)
- Stenotic canals (e.g. shar pei)
Predisposing causes - excessive moisture
- Environment (heat & high humidity)
- Water (swimmer’s ear, grooming, cleaners)
Predisposing causes - obstructive ear dz
- Feline apocrine cystadenomatosis
- Neoplasia & polyps
Predisposing causes - primary otitis media
- Primary secretory otitis in CKCS, tumour or sepsis
Predisposing causes - tx effects
- Altered normal microflora (e.g. inappropriate cleaner)
- Trauma from cleaning or plucking
Primary causes
Parasites
- Otodectes cynotis
- Demodex spp.
- Scabies
Foreign bodies
- Grass awns
Hypersensitivity
- Atopic dermatitis, food hypersensitivity, medications
Keratinisation disorders
- Primary idiopathic seborrhoea
- Hypothyroidism
Glandular disorders
- Cocker spaniels, English springer spaniels & Labrador retrievers have increased ceruminous glands
Miscellaneous
- e.g. feline proliferative & necrotising otitis externa
Otodectes cyanotis
- Common cause of otitis
hypersensitivity disease
– Carrier / non-clinically affected state
– Hypersensitivity disease
– Ectopic disease - Most ear creams are effective with localised disease
–Selamectin or moxidectin spot-on
–Likely that the isoxazoline group are effective - May need a cleaner ± steroids
- Lays long eggs
- Usually brown wax
- Run away from light when put otoscope on them
- Can be very sore
Foreign body otitis
- Grass seeds most common
– Late spring to end of summer
– Often stimulate violent response in the affected individual – sudden onset
– Check the other ear
– Can be hidden in discharge and migrate into middle ear - Painful - chemical restraint is essential in most.
- Beware the hair that looks like a grass seed and vice versa
- Explosive onset (driving it mad)
- Few days of anti-inflammatory steroids useful
Hypersensitivity otitis
- OE is a VERY common complication of atopic dermatitis and food allergy
- Primary otitis is often not recognised and so inadequately treated and dogs and cats present when there is secondary infection
- Prevention of recurrence
– Treat 1˚disease
– Ensure perpetuating factors are treated
– Ensure owner knows to intervene early
Secondary disease - Bacteria
acute disease (generally):
- Gram-positive bacteria
– Staphylococcus species
– Streptococcus species
– Corynebacterium species
– aka commensals of the normal ear
chronic disease (generally):
- Gram-positive bacteria
– Enterococcus species
- Gram-negative bacteria
– Pseudomonas species
– Proteus species
– Escherichia coli
– perpetuating changes, thickening, lack of epithelial migration -> tend to get things from the environment
– trickier to deal with
Secondary disease - Fungi
- Acute & chronic disease
– Malassezia spp.(common)
->Malassezia pachydermatis
->Lipid dependent Malassezia spp.
– Candida spp. (uncommon)
– Aspergillus spp. (v. v. uncommon)
Some Candida spp in people and occasionally in dogs are very dangerous re drug resistance in people
Perpetuating factors
- Pathological changes in the external ear canal (change sin canal wall, changes in glandular tissue, changes in the tympanum)
- Otitis media
Hidradenitis
= inflammation around ceruminous glands (more generally around sweat glands)
Perpetuating factors - changes in canal wall
- Inflammation causing failure of epithelial migration
- Acute change: oedema, hyperplasia
- Chronic change: proliferative change, canal stenosis, calcification of pericartilaginous fibrous tissue
Perpetuating factors - changes in glandular tissue
- Hyperplasia of ceruminous and sebaceous glands, hidradenitis
- large increase in ceruminous gland -> useless/unhelpful wet watery wax
Perpetuating factors - changes in the tympanum
- Dilation, rupture, diverticulum (false middle ear – cholesteatoma)
Perpetuating factors - otitis media
Acute
- foreign material
- mucopurulent exudate
Chronic
- biofilm formation
- granulation material
- bony change in the bulla
Clinical signs of OE - Presenting reasons
- Aural / otic pruritus or headshaking
- Mild to marked exudate
- Malodour
- Head tilt
– Neurological or pain - Deafness
– Often conduction
– May be toxic / neurological
Clinical signs of OE - physical findings
- Erythema, swelling, scaling, discharge (otorrhea), malodour and pain
- Secondary
– pinnal lesions are common
– pyotraumatic dermatitis
– haematoma (due to damaged blood vessels)
Disease progression
- Secondary disease follows the primary cause
- Many / most cases are not presented until secondary disease is present
– Malassezia
-> Staphylococci
-> Gram negative rods
– If treated inadequately potential for anti-microbial resistance - In many cases Pseudomonas aeruginosa is end point
- Progressive pathological changes occur with time
Microbial progression
- Dysbiosis (cytology unremarkable) –> Erythroceruminous OE (cytology shows increase in commensal microbes) –> Purulent OE (cytology shows neutrophilic inflammation & microbes)
- once becomes OE: Mallassezia +/- Staph -> Staph -> Gram negative rods (often Pseudomonas)
- Multiple tx along the path means huge potential for antimicrobial resistance
Progressive pathological changes that occur as the disease progresses over time
- Epidermal hyperkeratosis and hyperplasia
- Dermal oedema
- Fibrosis
- Ceruminal gland hyperplasia and dilation
- Abnormal epithelial cell migration
- Tympanic membrane alterations
- Otitis media (16% of acute OE, 50–80 % of chronic OE)
Swimmers ear
- usually Pseudomonas
To pluck the ear hair or not?
- Remove loose hair that’s in telogen at the top -> will come out easily and quickly
- Don’t remove those in anagen -> will hurt and cause damage which can/will lead to otitis externa
History and examination
General health / other skin disease
- e.g. inappetence /difficulty eating, signs of atopic dermatitis
Specific ear history points
- Unilateral / bilateral
- Pruritus / head shaking / scratching
- Smell
- Head tilt
- Signs of facial paralysis
General clinical examination / other skin disease
Neurological problems
Ear carriage
Pinna and outer meatus and upper vertical canal
Smell
Always check both ears
Otoscopy
- Assistance for restraint
- Pain
– Do not look?
– Admit for chemical restraint?
– Treat for short period and then reassess? - Fear
– As for pain, or pretreatment with anxiolytic (e.g. trazadone)
– Need a long-time solution! - Look at the good ear first
- Head forward and slightly downwards
- Straighten canal and use a small cone
- Cones must be sterilised between use
- Some dogs loathe their noses being held tight
- Either use a muzzle so there is no pressure, or consider holding side of head (care)
- If the head moves a lot during otoscopy, the procedure is likely to be painful
- Chill protocol (Gabapentin and Trazadone can be useful)
Examination points
Canal
- Wall - swelling ulceration, hyperplasia, hair, masses, redness
- Lumen - wax, pus, ear mites, foreign bodies and occlusion
Drum
- Present or absent, changes in colour, bulging?
Discharge / cerumen
- What is normal? wax in rings seemingly coming up the ear canal is normal
– No wax is unusual
– Heaped up or spread along the canal
- Colour
- Texture
Smell
- Useful as a measure of infection in many cases
Cytology & wax exam
- Usually possible, even when otoscopy is not
- Best practice – perform in ALL cases
- Affected by treatments which are often oily
- Consider taking bacteriology swab with cytology and then submit, store or dispose
Sampling
Parasites (Otodectes & Demodex)
- Mix gently in LP and coverslip
Wax samples
- Poor stickiness
- Use staining rack
- Apply methylene blue only and coverslip
Purulent samples
- Stain as for cytology
Biofilm
- A common finding in otitis due to bacteria (and yeasts)
- Biofilms = extracellular matrix material produced by bacteria, usually when the bacteria are in larger numbers and in close proximity.
- Quorum sensing between bacteria leads to
– Biofilm production
– Increased toxin production - Leading to lack of penetration of antibiotic and disinfectant agents
- Increased difficulty in cleaning
- ‘snotty/mucoid/tenacious appearance’
- marked neutrophilic exudate due to increased toxin production
Biofilm - cytology
- Lacey/filigree matrix material and zones of none or different staining material around organisms
Bacteriology
- Confirms and/or identifies bacteria present in the ear canal
-Presence of bacteria ≠ disease – the ear is not sterile - Commonly affected by
– Previous antibiotic ear creams
– Previous otic cleaners - Provides susceptibility data
– MIC and disk diffusion techniques
– Flawed when considering topical treatment
– e.g. MIC resistance > 64µg marbofloxacin needed, in cream delivering 3000µg/ml = 45 X more
– This still may be ineffective for some bacteria with very effective efflux pumps systems or that produce large amounts of biofilm
Indications - bacterial culture in otitis - cytological reasons
- Rods are seen. The most suitable antibiotic treatments can only be chosen if the organisms are known
- Marked purulent or pyogranulomatous discharge without organisms being noted. Possibility of finding a pathogen that is relevant, but also may grow organisms that are irrelevant clinically.
Indications - bacterial culture in otitis - clinical reasons
- In the event of treatment failure.
- If there is a suspicion of meticillin-resistant Staphylococcus species (MRS).
- If considering video otoscopy or ear flush for diagnosis or treatment in a bacterial otitis as in the event of an adverse event following these procedures, systemic antimicrobials may be required.
