VESTIBULAR SYSTEM AND NYSTAGMUS

Vertigo and dizziness are common complaints encountered in general pra ctice. In most cases, the symptoms are caused by a mismatch between th e visual, vestibular, and somatosensory systems resulting in a so-call ed ''sensory conflict''. Knowing the basic physiological principles of the vestibular system is mandatory for the understanding of the patho genesis of vertigo and dizziness. Based on this knowledge the main tas k of the clinician is to obtain a good description of what the patient means by dizziness. Finally, a thorough otoneurological evaluation is needed to identify the specific pathology behind the patient's compla ints. If the patient reports an illusion of movement (vertigo), this m ost likely indicates an imbalance within the vestibular system. A sens ation of rotatory movement together with a spontaneous nystagmus sugge sts a lesion involving the semicircular canals, while an illusion of l inear movement indicates a disturbance of the otoliths. Nystagmus of c entral origin or caused by a peripheral vestibular lesion can usually be distinguished based on other features in the history or on clinical examination. While peripheral vestibular lesions usually lead to a mi xed horizontal-torsional or vertical-torsional nystagmus with constant slow phase velocity, a pure vertical or pure torsional nystagmus is a lways caused by a central lesion.