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
