Few neurological presentations look quite as dramatic as acute vestibular disease. A dog that was normal the night before may suddenly be unable to stand, falling repeatedly to one side with a marked head tilt and nystagmus.
For owners, it can be terrifying. For vets, however, the most important first question isn’t necessarily what disease does this patient have?
It’s:
Is the vestibular disease peripheral or central?
Getting that localisation right dramatically changes the differential diagnoses, investigations, prognosis and conversations we have with owners.
Recognising vestibular disease
The vestibular system keeps the head, eyes and body correctly orientated in relation to gravity. When it goes wrong, characteristic clinical signs include:
- Head tilt
- Vestibular ataxia, often with falling or rolling
- Nystagmus
- Positional strabismus
- Circling
- Nausea, vomiting and hypersalivation
Once you’ve recognised vestibular disease, the next step is to decide where within the vestibular system the problem lies.
Peripheral vestibular disease
Peripheral vestibular disease involves the inner ear or vestibular portion of cranial nerve VIII.
Typical findings include a head tilt towards the affected side, horizontal or rotary nystagmus and vestibular ataxia. Importantly, mentation and postural reactions should remain normal.
Because of their close anatomical relationship with the middle and inner ear, the facial nerve and sympathetic innervation to the eye can also become involved. This means ipsilateral facial paralysis or Horner’s syndrome can accompany peripheral vestibular disease.
Common causes include idiopathic vestibular disease and otitis media/interna.
Idiopathic vestibular disease can look particularly alarming, but the prognosis is generally very good. Signs occur acutely and can initially be severe, but improvement commonly begins within the first few days to weeks. A residual head tilt can sometimes remain.
When should you worry about central disease?
Central vestibular disease involves the brainstem or cerebellum.
The vestibular signs themselves can look remarkably similar to peripheral disease, so the key is to look for evidence that other parts of the brain are involved.
Features that should raise suspicion of a central vestibular lesion include:
- Altered mentation
- Postural reaction deficits
- Hemiparesis
- Other cranial nerve deficits
- Cerebellar signs
- Vertical nystagmus
One particularly useful principle is that postural reaction deficits are not expected with straightforward peripheral vestibular disease. Their presence should therefore make you look much harder for a central lesion.
Don’t let the head tilt fool you
Most vestibular lesions cause a head tilt towards the side of the lesion.
But there is an important exception.
Lesions involving the vestibular components of the cerebellum can produce paradoxical vestibular disease, in which the head tilts away from the lesion, due to loss of ipsilateral inhibition.
The clue is the rest of the neurological examination. A patient with a right head tilt but left-sided proprioceptive deficits, for example, should make you consider a left-sided central vestibular lesion.
What happens next?
Once you’ve decided whether the disease is peripheral or central, the diagnostic investigation becomes much more focused.
Peripheral disease may warrant careful examination of the external and middle ear and, where appropriate, advanced imaging. Importantly, an apparently intact tympanic membrane does not exclude middle-ear disease.
Central vestibular disease usually warrants investigation of the brain, most commonly with MRI, with CSF analysis considered depending on the imaging findings.
Potential causes range from inflammatory and infectious disease to neoplasia, toxicity and cerebrovascular disease.
The Movement message
Don’t be distracted by how dramatic the patient looks. Localise first.
A profoundly ataxic dog with a severe head tilt and nystagmus may have benign peripheral vestibular disease and an excellent prognosis. Conversely, a patient with relatively subtle vestibular signs but proprioceptive deficits or altered mentation may have significant intracranial disease.
At Movement Referrals, our neurology team uses the neurological examination to establish the likely lesion localisation before deciding which investigations are actually needed.
Because in veterinary neurology, getting the localisation right is often the most important step towards getting the diagnosis right.