Flashcards in Lecture 2 Deck (40):
What is the external ear canal comprised of?
The external ear consists of skin overlying cartilage.
- Auricular cartilage = ventral canal
- Annular cartilage = horizontal canal
When the external ear canal becomes inflamed, it swells internally into the lumen of the canal!!
External ear canal like the drain on a sink?!
The horizontal canal of the external ear run distally from the skull, and then dips down like the trap in a sink drain. After this sink trap, the ventral canal then rises dorsally to the external auditory meatus.
- Debris trying to get out of the horizontal canal tends to get lodged in this sink trap!!
Can there be hair in the external ear canal?
There are hair follicles in the inner ear canal of all dogs/cats.
- This means they can develop folliculitis/furunculosis in the ear!!
What order are the bones of the ear in?
Malleus (embedded in ear) ===> Incus ===> Stapes
If you are looking at the tympanic membrane, you should be able to see the malleus embedded in the tympanic membrane. Does the curvature of the malleus open cranially or caudally?
The curvature of the malleus opens (concave) towards the NOSE!
The pars flaccida lies just external to the tympanic membrane. Normally it does not obstruct visualization of the tympanic membrane.
- It may dilate and occlude sight of the tympanic membrane due to middle intra-ear pressure
==> tells you something is going on in the middle ear!
==> if it's too large, stick a needle in it and deflate it
Pathophysiology of ear disease: factors
1. Predisposing factors (ie. lots of swimming; breed)
2. Primary factors
3. Perpetuating factors
- Otitis media
#1 Cause of Ear disease
==> DOGS = Atopic Dermatitis
==> CATS = Ear Mites
Pathologic changes in the ear
1. Inflammation (edema and cellular infiltration)
2. Glandular hyperplasia
3. Epidermal hyperplasia (defense mechanism, skin gets thicker)
4. Migration of inflammatory cells, release of cytokines
What significance do hyperplastic glands in ear disease/otitis have?
Hyperplastic glands in the ear are significant as they dilute the ear wax ==> decrease the amount of lipid in ear wax
- this makes the ear less able to battle infections
Inflamed tissue can enlarge due to edema/infiltrates, why is this significant in otitis?
The ear canal is a finite space, inflammatory tissues of ear/ear canal can lead to a narrowing and/or obstruction of the ear canal!
What are defense mechanisms of the ear?
1. Self-cleansing mechanism (migration of keratinocytes)
2. Cerumen (ear wax)
- Sebaceous secretions
- Ceruminous (apocrine) secretions
Cerumen (ear wax)
MAJOR DEFENSE MECHANISM OF EAR!!
Components: secretions of sebaceous glands, ceruminous (apocrine) glands, epithelial cells
- Functions: lubrication, hydration, protection
- LIPID CONTENT DECREASES (49% to 24%) IN CHRONIC OTITIS EXTERNA (due to dilution by glands)
Clinical significance of Cerumen
Cerumen plays an important role in maintenance of a healthy ear
- changes of cerumen may result in serious consequences
- many drugs can influence cerumen contents
Hyperplasia of apocrine (ceruminous) dilutes lipid content of cerumen
- reduces antibacterial/antifungal effects
- glands may become infected and rupture --> pain
What are key diagnostic approaches to otitis
1. medical history
2. physical exam
3. otoscopic exam
5. Culture and senstivity
6. Diagnostic imaging
What is the KEY diagnostic test in otology?
- the key diagnostic test in otology
- need good technique, and a good microscope
Done in both ears, regardless if disease is unilateral, and at initial presentation and EVERY recheck examination! It's not an optional test!! You must do cytology!!
Where should you take your cytology sample?
Take cytology sample from entrance of the horizontal canal
How to sample the ear
W/ the ear pulled straight out, the swab should go in the ear parallel to the ground (K9 standing)
- place the swab in the notch at external auditory meatus
When creating a cytology slide sampled from the ear, how should you apply the swab to the slide?
ROLL the swab onto the slide! You don't want to smear things up..
Should you heat fix a slide sample from the ear?
If the prep on the slide is waxy, he DOES heat fixing
- it doesn't change the diagnosis but he thinks it makes it easier to make the diagnosis
Be very gentle or all the material will come off
~10 seconds in each solution
When you rinse with water at the end, don't jet the water directly on your sample, let it hit the slide above your sample and run down
- if the slide doesn't appear basically clear, you didn't rinse enough!!
What is normal in the ear canal?
- keratinocytes, sebum, ceruminous secretions (apocrine gland)
- VERY LOW numbers (if you see many the ear isn't doing its job!)
- Yeast and various bacteria
What are we looking for on ear cytology?
The presence of bacteria and/or yeast.
- relative amounts (single organism or multiple)
Other atypical cells (ie. neoplastic)
Parasites (not just Otodectes!)
What type of bacterial infection is easiest to manage?
A mixed bacterial infection (ie. cocci and rods)
- It has a better prognosis and is easier to manage
- No 1 bacteria had developed a population enough to kick the others out
What do the presence of WBC indicate?
WBC on ear cytology indicate damage to epithelium
Should I do a bacterial culture and susceptibility?
Not necessary in most cases.
- Known resistant organisms
- Failure to respond to standard of care therapy
- Previous administration of several antibiotics
- Single population of rods on cytology ==> probably PSEUDOMONAS
- concurrent systemic signs
KEY: Cleaning ears
1. removes debris that causes irritation
2. removes debris that blocks movement of medication into horizontal canal
3. removes debris that interferes with "self-cleaning"
4. removes debris (ie. pus) that can interfere w/ activity of active ingredients
- Many otic meds are inactive in the presence of abscesses
5. reduces burden of microogranisms
What to do w/ hair in the ears
Once otitis is present, hair should be removed
- prevents evaluation of entire ear canal and tympanum
- predisposing factor
- BLOCKS PENETRATION OF MEDICATION INTO EAR
Deep Ear Cleaning/Flushing
Indicated when you cannot clearly see the tympanic membrane
- cleaning the ear may be done through otoscope or video otoscope
- Techniques: special catheters, teflon-coated catheters, pump-suction instruments
ESPECIALLY IMPORTANT TO DEEP CLEAN IF PSEUDOMONAS IS PRESENT - crystal clear clean!!
Ceruminolytic agents are usually softening agents
- Squalene, DSS, urea
- Foaming agents: carbamine peroxide
Topical Otic Therapy
- delivers medication directly to affected area
- get high [ ] ===> can over-ride the defense mechanisms of some organisms by increasing [ ] of the antibiotic
- delivery deep into ear may be questionable if done by owner
- poor penetration if middle ear is involved
Best practices for Topical Otic therapy
1. Active ingredients: efficacy
2. Removal of obstructions: wax, hair
3. evaluate the integrity of the tympanum (CRITICAL if you are going to use ototoxic drugs, like aminoglycosides!!)
4. the formulation must facilitate distribution of medication DOWN the ear canal
5. Technique, frequency, and duration of administration (he does otic meds 1x/day!!!)
6. Volume per application (drug in ear could be shaken out, could be absorbed, could evaporate, could bind to something)
7. treatment times must be sufficient to clear infections
Volume Recommendations at ISU (K9)
<10 kg = 0.4 - 0.5 ml
10 - 20 kg = 0.5 - 0.7 ml
>20 kg = 1.0 ml
Negatives: increased cost due to increased volumes administered compared to the label; may be increased systemic effects
Long acting topical otic medications
Applied by the vet every 7-30 days
- carriers may include lanolin (messy, problematic), gel polymers, or lightweight oils
- generally, require clean prior to application
How long should folliculitis be treated? (including folliculitis in ear canal)
Folliculitis needs to be treated for 3-4 weeks!!!
General indications for systemic therapy (antibacterial or antifungal(
1. recurring or severe infections
2. concurrent infectinos elsewhere (ie. skin)
3. owners are incapable of medicating the patient
4. patients refuse to cooperate
5. when hyperplastic lesions prevent topical application of medications
6. known OTITIS MEDIA
Systemic therapy: specific indications
1. presence of inflammatory cells in cytology
2. ulcers present on otoscopic exam
3. single population of gram (-) rods in a recurring infection
4. systemic signs (ie. fever)
5. known OTITIS MEDIA
Glucocoriticoids in ears
1. Will be absorbed systemically and can result in systemic effects
2. Best practice is to use aggressively INITIALLY, then back off asap
3. If possible, use antiseptics... vs. antibiotics for long-term management
4. Almost always are good, if used EARLY!
Rechecks are necessary to monitor therapy
- will determine if treatment reduced infection (relapse) or cleared infection (BIG difference!)
Common otic health Maintenance Strategies
1. intermittent cleaning (w/ products w/ antimicrobial activity)
2. Use of antiseptics or astringents
ie. Vinegar and water
3. Intermittent use of mild glucocorticoids
- switch from potent agents to glucocorticoids that have fewer systemic effects (hydrocortisone, mometasone) for maintenance