Vestibular syndrome is not a disease per se but a conglomerate of neurologic signs due to a dysfunction in the vestibular
system, either peripheral or central.
Dr. Helena Rylander
Based on neurologic examination findings, a vestibular lesion can be localized to the peripheral or central vestibular system.1 This distinction is important since the differential diagnoses, work-up, treatment, and prognosis in patients with peripheral
vestibular dysfunction are different from those in patients with central vestibular dysfunction.
Here's how to first determine whether a vestibular problem stems from the inner ear or the brain and then how to pinpoint
the underlying cause and administer appropriate treatment.
PERIPHERAL VS. CENTRAL VESTIBULAR ANATOMY
The vestibular system maintains balance and coordinates the position of the head, eyes, neck, and limbs in space.
The peripheral vestibular system comprises three semicircular canals, the utricle and saccule in each inner ear, and the vestibulocochlear
nerve (cranial nerve [CN] VIII).2 The inner ear is located in the petrous temporal bone (Figure 1).
1. A CT scan of the inner ear in the petrous temporal bone (red circles).
The central vestibular system comprises eight vestibular nuclei in the brainstem (four on each side), two caudal cerebellar
peduncles, and the flocculonodular lobe of the cerebellum (Figure 2).1
The vestibular nuclei then project to the cerebellum, contralateral vestibular nuclei, reticular formation of the brainstem,
the spinal cord, the cerebrum, and the extraocular muscles via the medial longitudinal fasciculus and CN III, IV, and VI.1
2. MRI of the central vestibular system’s location in the brainstem and cerebellum (red circle).
SIGNALMENT AND HISTORY CLUES
Although rare, puppies may have a congenital peripheral or central vestibular disorder.3,4 Vestibular dysfunction due to neoplasia is more common in older dogs, although a primitive neuroectodermal tumor may cause
vestibular signs in a young dog.
Vestibular signs are often acute in onset regardless of the lesion's location. Metronidazole toxicosis as a cause of vestibular
signs may be supported by a history of metronidazole treatment. Dosages as low as 67.3 mg/kg/day in a dog and 58 mg/kg/day
in a cat have been documented to cause vestibular signs.5,6 I have diagnosed metronidazole toxicosis in a dog that received 40 mg/kg/day. A recent ear infection may precede peripheral
vestibular dysfunction. A systemic disease such as hypothyroidism or hyperadrenocorticism—possibly uncovered through a physical
examination and laboratory testing—may cause peripheral or central vestibular dysfunction.