Otitis interna

Question 1

Incidence

Answer 1

• unknown (rare)

Question 2

Causes

Answer 2

• extension of OM (majority)
• haematogenous and ascending infection via the auditory tube
• adverse drug reaction

Question 3

Clinical signs

Answer 3

• Head tilt to the affected side
• Spontaneous or rotatory nystagmus
• Asymmetric limb ataxia with preservation of strength
• Falling
• Vomiting and/or anorexia

Question 4

Differential diagnoses

Answer 4

• Other peripheral vestibular diseases
• Idiopathic vestibular syndrome (older dog)
• Neoplasia (vestibulocochlear nerve)
• Hypothyroidism

Question 5

What to do

Answer 5

• Seek advice from experienced or referral vets

Question 6

Diagnosis & tx

Answer 6

• Establish the presence of systemic disease and/or localised disease (OE/OM)
• Pruritus, headshaking and pain around the TMJ may be useful indicators of local disease
• Complete neurological examination
• Otic examination ± myringotomy
• MRI (possibly CT)
• In the absence of another cause, long term use of systemic antibiotics has been advocated.
  – Ability to cross the BBB
  – Based on culture of the middle ear?
  – Don’t tend to use systemic AB for OE or OM but potentially justified for OI

Question 7

Ototoxic neurological signs

Answer 7

• Profound hearing loss and vestibular signs may be seen
• No inner ear tx is considered otosafe (always risk)
• Complicated by competing signs from bacterial toxins/invasion and inflammation

Question 8

Suspected adverse drug incident - What to do

Answer 8

1. Seek specialist advice / consider referral
2. Remove the product from the ear as soon as possible
   - Repeat cytology and bacteriology
   - Anaesthesia and flush the area gently with saline
3. Give high anti-inflammatory dose of dexamethasone systemically
4. Consider the use of appropriate antibiotics (choose a drug that crosses BBB)
5. Withdraw topical therapy temporarily
6. Report to the manufacturer / Veterinary Medicines Directorate