Otitis 1 Flashcards
Describe the tympanic bullae in dogs and cats
Cat – bony shelf that extends completely throughout the tympanic bullae, separating it into two halves – can make treatment difficult
In dogs it is more open
Which nerve is found in the middle ear?
Facial
Describe the histology of the ear canal
Ear canal lined by modified skin
Small hairs
Ceruminous glands
Sebaceous glands
Describe the histology of the middle ear
Middle ear lined by modified respiratory epithelium
Simple squamous to cuboidal
Few ciliated cells
Mucous-secreting goblet cells
Why do ears not need to be cleaned?
Self-cleaning mechanism - Only need to be cleaned when the ears are diseased and the self cleaning mechanism has stopped working
What is cerumen?
‘Ear wax’
- Sebaceous & ceruminous gland secretions
- Catches foreign material, desquamated keratinocytes & microbes
- Contains antimicrobial peptides and Igs
What are the two key features of the self-cleaning mechanism of the ear?
Cerumen
Epithelial migration - living keratinocytes carry cerumen and contents out of canal
What is the function of the Eustachian tube?
An opening that connects the middle ear with the nasal-sinus cavity:
- Drains mucous from middle ear cavity into nasopharynx
- Equalises air pressure either side tympanic membrane
Which microbes are normally present in the external ear canal?
- Gram +ve cocci predominate: Staphylococcus pseudintermedius, S. schleiferi
- Coagulase –ve staphylococci
- Streptococcus spp.
- Micrococcus spp.
- Malassezia spp.
- Middle ear commensals similar to URT flora
Name some causes of pruritic pinna disease
- Sarcoptic mange (scabies)
- Neotrombicula (harvest mites)
- Allergic skin disease (CAD)
- Pemphigus foliaceous
- Contact irritant dermatitis
- Fleas
- Aural haematoma
Name some causes of non-pruritic pinna disease
- Vasculitis
- Pinnal margin seborrhoea
- Squamous cell carcinoma
- Hyperadrenocorticism and hypothyroidism
- Pemphigus foliaceous
- Auricular Chondritis
Define primary and secondary causes of otitis
Primary = induce otitis in normal ears
Secondary = promote otitis in abnormal ears
What are predisposing factors?
Present prior to otitis and make it more likely to develop
What are perpetuating factors?
Result from inflammation and prevent resolution
List the primary causes of otitis in dogs
- Foreign bodies - Plant awns, foxtail, hair, sand
- Allergic skin disease - atopic dermatitis, adverse food reaction, flea bite hypersensitivity, contact allergy
- Bugs - Otodectes, Demodex, trombiculids, ticks
List the primary causes of otitis in cats
- Flu - FCV, FHV, (FeLV, FIV), canine distemper
- Allergic skin disease - atopic dermatitis, adverse food reaction, flea bite hypersensitivity, contact allergy
- Bugs - Otodectes, Demodex, trombiculids, ticks
What is hypersensitivity otitis - how does it present?
- OE common manifestation of AD
- Pruritus present
- May be history of generalised pruritic skin disease or only otitis
- Dogs often meet Favrot’s criteria for diagnosis CAD either way but cats (FASS) may not
What is the most common cause of foreign body otitis
Grass seeds most common
- Late spring – end of summer
- Acute onset, violent response
- Can be hidden in wax and migrate into middle ear
- Painful (chemical restraint required)
- Beware the hair that looks like grass seed and vice versa
How does Otodectes cynotis present?
- Dark ‘coffee ground’ wax, small white mites
- Most patients have HSR to mites > intense pruritus
- Ectopic disease (mites leave ear canal and affect haired skin e.g. tail tip in cats)
- Mites photophobic so if not seen otoscopically sample ear
How is Otodectes cynotis diagnosed?
Indirect smear using cotton bud
Collect wax from EEC
Mix with liquid paraffin on slide
Cover slip and microscopy x4
How is Otodectes cynotis treated?
- Most oily topical ear products effective with localised disease (smother mites)
- Selamectin or moxidectin spot-on
- Evidence that isoxazoline group effective*
- May need steroids to manage inflammation and pruritus
List some secondary causes of otitis
- Microbial infection
- Topical medication reaction (Irritation of inflamed skin by alcohol, acid, propylene glycol)
- Inappropriate cleaning (Physical trauma, excessive moisture and maceration)
List a predisposing factor for obstructive ear disease
Neoplasia and polyps
How can conformation of ears act as a predisposing factors for ear disease?
Hairy canals (e.g. poodle)
Narrow canals (e.g. Shar pei)
Waxy canals and hairy pinnae (cocker spaniel)
Pendulous pinnae (e.g. bloodhound)
