Otitis Externa:Pathogenesis, Treatment & Preventative

Maintenance

© All photos are copyright of CE Griffin, REW Halliwell, DN Carlotti & DH Lloyd

Anatomy

Ear canal

Cartilage

Tympanum

Otitis externa

Inflammation & infection of the ear canal

Pathogenesis

INFLAMMATION

Epidermal hyperkeratosis & sebaceous glands hyperplasia

Increased desquamation & sebaceous secretion

Accumulation of cerumin & debris

INFECTION

Pathogenesis

Primary factors

Predisposing factors

Perpetuating factors

Multi-factorial

Pathogenesis

Predisposing factors

Factors that alter the environment of the ear canal, making the latter more susceptible to bacterial & fungal infections.On their own, these factors do not give rise to otitis externa.

No treatment is possible, only preventative maintenance.

Pathogenesis

Predisposing factors

Abnormal anatomy

Excessive moisture

Treatment errors

Neoplasm

Polyp

Pathogenesis

Primary factors

On their own, these factors can induce or initiate otitis externa.

Treatment is possible for some of the factors but requires patience and step-wise approach to establishing them.

Pathogenesis

Primary factors

Parasites

Allergies

Defective keratinisationForeign bodies

Onset: erythema

Pathogenesis

Primary factors

Parasites : Otodectes cynotis

• Extremely contagious.

• Only a small number of mites are needed to trigger the disease, through induction of an allergic reaction.

• In recurrent cases, consider the presence of asymptomatic carriers of ear mites in the same household.

Otodectes cynotis: black cerumin

Pathogenesis

Primary factors

Allergies:

• 30% of allergy cases, otitis externa is the initial and only clinical sign detected.

• 83% of animals with atopy have concurrent otitis externa.

• 80% of animals with food allergy have concurrent otitis externa.

• Up to 90% of animals with FAD have concurrent otitis externa.

Atopy

Pathogenesis

Cocker spaniel

Primary factors

Defective keratinisation:

• Genetic disorder of certain breeds like Boxer, Cocker Spaniel, Doberman, German Shepherd Dog.

• Epidermal hyperkeratosis, sebaceous gland hyperplasia.

• Defective cerumin (increase in free fatty acids and de-esterified wax).

Pathogenesis

Primary factors

Foreign bodies:

• Plant materials.

• Excessive hair.

• Dried-up medication, e.g. ointment.

• Dirt and sand particles.

Grass awn

Pathogenesis

Perpetuating factors

These factors will not initiate the onset of otitis externa,but will prevent its resolution.

They are bacteria & yeast. Up to 50% of a healthy ear have a positive culture of a variety of commensal and potentially pathogenic bacteria.

Treatment is of prime importance for the veterinarian.

Pathogenesis

Perpetuating factors

Organism Occurrence

1. Malassezia spp.

2. Staphylococcus coagulase +

3. Pseudomonas

4. Proteus

5. Streptococcus

6. Gram –ve bacteria

30%

30%

20%

10%

< 5%

< 5%

© Shipstone in ASAVA Conference (2000)

90%

Diagnosis

Otoscopic examination

Perform an otoscopic examination of the ear canal precedent to a dermtological examination.

Sedate or anesthetize animal if necessary (proper restraint will prevent further damage of the ear canal).

Perform examination under bright florescence lighting.

Diagnosis

Otoscopic examination

Important changes to note:• Type of pinnae

• Degree of erythema & edema

• Presence of proliferativechanges in the canals, or foreign bodies or parasites.

• Diameter of canals.

• Nature of discharge.

• Integrity of tympanum.

Diagnosis

Otoscopic examination

Impact of the middle ear:

• Head tilt or facial nerve damage.

• Prognosis guarded.

Diagnosis

Cytology• Incorporate in the practice for all cases of otitis externa.

• Simple and valuable tool.

• Repeat at subsequent visits, always.

• Legitimate supplemental income for the practice.

Organism Sensitivity of detection

1. Gram +ve

2. Gram -ve

3. Malassezia

84%

100%

100%© Shipstone in ASAVA Conference (2000)

Diagnosis

Cytology : ear mites

Otodectes cynotisin oil immersion

Diagnosis

Cytology : cocci

Intracellular cocci

Neutrophils

Diagnosis

Cytology : Malassezia

Budding cells

Diagnosis

Culture & sensitivity tests

Expensive and no more valuable than cytology.

Not indicated at first visit or first occurrence of otitis externa.

Can be considered in chronic and recurrent cases, or when there is real failure to respond to therapy.

DiagnosisThorough

cleansing of earOtoscopy &

Cytology

Involvement of O. cynotis onlyBacteria & Yeast

Topical & systemic therapy Topical therapy only

Relapse Poor response

Good response CURE

Otoscopy, Cytology, C&S Test.

Further cleansing.

Reassess the P3

Continue treatment regimen.

Initiate preventative maintenance.

Reassess treatment regimen

Treatment

3 majors stages

1) Ear cleaning with management of the predisposing causes

2) Treatment of perpetuating causes

3) Identification and treatment of primary causes

Treatment

1) Ear cleaning and predisposing causesImportance of ear cleaning:• remove irritating agents• facilitate the contact between the medicament and the ear canal wall• reduce microorganisms proliferation

Conditions for cleaning:• Under general anesthesia : ideal• If anesthesia is not possible (refused by the owner, current health state of the animal, not severe canal occlusion and exudate) utilisation of products with both cleansing and drying properties.

Predisposing causes :• Surgical removal (abnormal anatomy, neoplasm), cleasing/drying agent (excessive moisture), rechecking (treatment error)

Treatment

2) Treatment of perpetuating causesRequirement:• Efficacy against bacteria and/or yeast• Reduction of the inflammation (corticosteroids)

Conditions of treatment:• Essentially topical treatments (twice daily)• Clinic and microscopic examination after 15 days• Keep the ear clean (see above, “Ear cleaning”)

Treatment

2) Identification and treatment of primary causesParasites:• acaricides effective against Otodectes or Demodex (rarely)

Allergies:• The ear’s problem is a part of a general disease (Cf allergies’ treatment)

Defective keratinisation:• Mostly caused by an idiopathic seborrhea (long term corticosteroids therapy), sometimes endocrinopathy (hypothyroidism)

Foreign bodies:• Light surgery (NB : both ears must be examinated)

Treatment

Eliminating the inflammation

Corticosteroids are the drug of choice for topical therapy.

High anti-inflammatory (A.I.) activity is desirable for rapid remission and better pet owner compliance.

Longer biological half-life ensures that the A.I. activity is prolonged and the dose used is small to avoid side effects.

Treatment

Eliminating the inflammation

Corticosteroid A.I. Activity Biological Half-life

HydrocortisonePrednisoloneTriamcinoloneDexamethasoneBetamethasone

1452530

8 – 12 hrs12 – 36 hrs24 – 48 hrs36 – 54 hrs36 – 54 hrs

© W.B. Saunders Co. in Current Veterinary Therapy (1995)

Treatment

Eliminating the infection

Antibiotics Proteus Pseudomonas Staphylo-coccus

AmipicillinChloramphenicolGentamycinNeomycinPenicillinPolymyxin BStreptomycinTetracycline

RRS

S/ rR

S/ rs/ Rs/ R

RS/ R

SS/ rRR

s/ Rs/ R

S/ RSSSRSSS

© W.B. Saunders Co. in Current Veterinary Therapy (1995)

Treatment

Eliminating the infection

Broad spectrum antibiotic that can eliminate Staphylococcus, Pseudomonasand Proteus. Gentamycin

}Fungicide to eliminate the Malassezia. ThiabendazoleAcaricide to eliminate the ear mites.

Preventative Maintenance

In the majority of cases, the permanent correction of predisposing and certain primary factors is not possible:

•Abnormal anatomy

•Excessive moisture

•Atopy

•Defective keratinisation

Preventative Maintenance

The purpose of preventative maintenance is to reduce the risk of

recurrence and to reinforce the benefit of therapy. The pet owner should

perceive that his/her efforts and money dispensed in treating the pet is not

diminished by frequent recurrences.

Preventative Maintenance

Preventative maintenance of the ear should therefore include:

• Regular clipping of the hair on the inside of the pinnae.

• Gentle plucking of excessive hair.

• Routine use of a well adapted cleansing agent to minimize build-up of the perpetuating factors.

Preventative Maintenance

Criteria for choosing a cleansing agent

It is beneficial to the pet that is strongly predisposed to otitis externa to have its ear canals cleansed regularly, as this will minimize build-up of the perpetuating factors. This can be

done after every shampooing to ensure that no excessive moisture is left behind in the ear canal to cause maceration,

excessive production of cerumin and subsequent inflammation.

Preventative Maintenance

Criteria for choosing a cleansing agent

Mildly ceruminolytic for frequent usage:propylene glycol, lactic acid

Mildly drying so as not to be irritating:sodium ducosate

Antiseptic to control the bacteria & yeast population:lactic acid, parachlorometaxylenol

Mildly keratolytic so as to reduce excess cerumin:lactic acid, salicylic acid

Non-traumatic for the pet:self-cleaning fluid

Preventative Maintenance

Combination of active agents

© DH Lloyd et al., 1998, Vet. Rec., 143:111-112

“ The cleansing agent clearly has potent antimicrobial activity.(…). It is likely that the low pH created by the lactic and salicylic acid is involved in its antimicrobial action but the antibacterial and antifungal activity of

propylene glycol and parachlorometaxylenol may also be important. Penetration of these agents is probably

facilitated by the surface active properties of sodium ducosate.”