32 Otogenic intracranial infection
The initial presentation may include vestibular disease, facial paralysis or Horner’s syndrome.
Chronic ear infection can result in pyogranulomatous otitis media-interna with osteomyelitis of the tympanic bulla. Extension into the cranial vault is detected on MRI as a globoid or plaque-like mass extending from the bulla into the cerebello-medullary angle. This compresses the brainstem, and causes meningoencephalitis. Abscess formation may be seen as a thickened rim around the mass. Material is seen within the bulla.
Somewhat surprisingly, there may be no clinical indication of intracranial extension. Head or neck pain, depression, lethargy, seizures, and CN V deficits are not routinely found. A mild to moderate increase in rectal temperature (39–40°C) may be present. Haematology is normal or shows a mild neutrophilia. It should be suspected in any age or breed of cat or dog with chronic, recurrent, or existing otitis media-interna that develops vestibular signs (peripheral or central) over a period of hours to days. Most cases have been reported in the cat.
There had been a few days of lethargy before the spontaneous nystagmus, right head tilt and ataxia occurred. Treatment with dexamethasone and amoxicillin/clavulanic acid for 5 days appeared to lessen the ataxia but the cat became inappetant and would not move from its bed. No history of ear disease was reported but the cat was seen to scratch at the right ear before the balance loss occurred.
Examination found an alert ambulatory ataxic cat which lost balance when looking up, lurching to the right but not falling. A right head tilt was obvious. Spontaneous nystagmus was not present at rest or when the neck was dorsiflexed. The vestibulo-ocular reflex was slow to the right. Right facial paralysis was present. STT was normal bilaterally. No anisocoria was present. The placing response was slow in the right forelimb. Hopping was slightly reduced in the right fore- and right hindlimbs. Spinal reflexes were normal. No spinal pain was found.
The lesion was localized to the right facial nerve and the right vestibular apparatus. The right-sided postural deficits indicated right brainstem involvement. The CNN VII and VIII could be involved together by middle and inner ear lesions respectively, or by a right brainstem lesion picking off the nerves. The lack of spontaneous nystagmus in an ataxic cat with a head tilt is unusual and may indicate cerebellar involvement as the cause of the vestibular signs.