Pathophysiology of vestibular symptoms and signs: The clinical examination

A challenge for the clinical neurologist is to decide which of the myriad patients with symptoms of dizziness, lightheadedness, or imbalance have a genuine vestibular disorder, be it peripheral or central. The clinical examination is often the key. A series of systematically applied, physiologically based maneuvers, designed to probe static and dynamic function of the vestibulo-ocular reflexes and the individual labyrinthine sensors, will almost always reveal the evidence of a vestibular system anomaly, which either clarifies the diagnosis or points to a need for a further evaluation.This chapter will describe these maneuvers and indicate their diagnostic usefulness. They include dynamic visual acuity, occlusive ophthalmoscopy, head impulse (rotational vestibulo-ocular reflex) and head heave (translational vestibulo-ocular reflex) testing, mastoid vibration-induced nystagmus (equivalent of a hot-water caloric stimulus in a patient with unilateral vestibular loss), hyperventilation-induced nystagmus (abnormal in fistula, craniocervical junction anomalies, compressive and demyelinating lesions, and cerebellar degenerations), Valsalva-induced nystagmus (abnormal in fistula and craniocervical junction anomalies), head-shaking-induced nystagmus (vertical nystagmus after horizontal head shaking points to a central disorder), positional nystagmus (lateral canal, posterior canal, central) and sound-induced nystagmus (superior canal dehiscence). When combined with a careful examination of eye alignment, gaze holding, saccade accuracy and speed, and smooth pursuit, a central or peripheral localization is usually possible.