Vestibular disease is localized to the peripheral vestibular system, central vestibular nuclei, or cerebellum. Localizing vestibular syndrome is one of the biggest challenges in neuroanatomic localization! All three localizations can look similar at first, but here are some tips to help you localize vestibular syndrome consistently.
The key to localizing vestibular disease is proprioceptive testing. It can be difficult for an ataxic, disoriented patient to stand up for postural reactions, but it is of the utmost importance in making an accurate neuroanatomic localization.
Peripheral vestibular disease will never cause a postural reaction abnormality because the peripheral vestibular system, comprised of the semicircular canals of the ductal labyrinth in the inner ear, the receptors of the vestibular nerve, and the vestibulocochlear nerve (cranial nerve VIII), are located outside of the pathways for limb proprioception. In peripheral vestibular syndrome, the head tilt will be TOWARD the lesion, pathologic nystagmus AWAY FROM the lesion and NO postural reaction abnormalities are identified.
Central vestibular disease causes decreased or absent postural reactions because the brainstem lesion interrupts proprioceptive pathways coming and going through the medulla. Brainstem disease causes ipsilateral neurologic deficits. In central vestibular syndrome, the head tilt will be TOWARD the lesion, pathologic nystagmus AWAY FROM the lesion and postural reaction abnormalities will be IPSILATERAL to the lesion.
Paradoxical vestibular disease denotes disease of the cerebellum. Remember that the cerebellum’s output is always inhibitory—paradoxical vestibular syndrome represents a loss of inhibition over one side of the vestibular system. The cerebellar disease causes ipsilateral neurologic abnormalities. The paradoxical vestibular disease causes abnormal postural reactions that may be decreased or increased compared to normal. The cerebellum is responsible for unconscious proprioception, so it makes sense that proprioception decreased with cerebellar disease. However, the cerebellum is also responsible for controlling the smooth motor responses in proprioceptive testing. Having lost inhibitory control of movements, the patient can display an exaggerated postural reaction (best noted on hopping). In paradoxical vestibular syndrome, the head tilt will be AWAY FROM the lesion, pathologic nystagmus TOWARD the lesion and postural reaction abnormalities will be IPSILATERAL to the lesion.
Here are some other tips to help discover a vestibular localization:
- More often rotary, vertical, positional or changing pathologic nystagmus tend to be associated with central or paradoxical vestibular syndromes, although this is not a definite rule
- Patients with the central vestibular disease will likely have other brainstem signs, such as decreased mentation, weakness or other cranial nerve abnormalities
- Patients with the paradoxical vestibular syndrome will likely display other signs of cerebellar diseases, such as intention tremors and truncal sway
- Peripheral vestibular syndrome is often secondary to otitis media. Other neurologic signs associated with disease of the middle ear are ipsilateral facial paresis/paralysis and Horner’s syndrome
If you are in doubt about a patient’s localization, it never hurts to refer for a brain MRI and other possible neuro diagnostics. A brain MRI allows for good visualization of the entire vestibular system, including the inner and middle ears, the brainstem, and the cerebellum. Contact Veterinary Referral Surgical Practice Neurology/Neurosurgery at 770-594-2603 if you would like to refer your vestibular patient to Dr. Narak.