Utility of the hyperventilation test in the evaluation of the dizzy patient.

PURPOSE OF REVIEW: The aim of the review is to value the incidence, patterns and temporal characteristics of hyperventilation-induced nystagmus (HVIN) in patients suffering from vestibular diseases, as well as its contribution to the differential diagnosis between vestibular neuritis and schwannoma of the eighth cranial nerve and its behavior in some central vestibular diseases.

RECENT FINDINGS: The hyperventilation test seems to be more useful than other bedside tests in detecting schwannoma of the eighth cranial nerve in the case of sudden monolateral hypacusia. The presence of an excitatory pattern of HVIN in vestibular schwannoma that has undergone to stereotactic surgery reveals that this therapy produces demyelinization in neural fibers.

SUMMARY: The hyperventilation test is easy to perform, well tolerated and able to reveal latent vestibular asymmetries; it acts both at peripheral and central vestibular levels through metabolic mechanisms or, more rarely, through changes in cerebrospinal fluid pressure. It can provide patterns of oculomotor responses suggesting the execution of gadolinium-enhanced MRI, upon the suspicion of schwannoma of the eighth cranial nerve or of a central disease. In our opinion, the presence of HVIN always needs to be viewed within the more general context of a complete examination of auditory and vestibular systems.