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Relevance of function tests in the diagnosis of vestibular disorders.

The diagnostic value or relevance of a vestibular function test is dependent on the whole clinical and functional context of each particular case. It is not the ability to show 'abnormality' in a high number of patients complaining of whatever kind of vertigo, that indicates the relevance of a function test. Neither is relevance of a test based upon the possibility that this test can re-categorize some patients in the same way as has been done by other tests. Each test evaluates some particular functional aspect and this is very different from one test to another. A test is more relevant, i.e. indicates more abnormality when the type of vertigo caused by the dysfunction is also considered. These statements are confirmed by experience in peripheral vestibular disorders, especially benign paroxysmal positional vertigo (BPPV). A paroxysmal positional nystagmus (ppn) (nystagmus and vertigo elicited by movements and manoeuvres) is linked to the problem of provoked vertigo and gives a confirmation of this vertigo by reproducing it in some manoeuvres. Some inconstancy in the reproduction of this ppn may cause difficulties in diagnosis. Caloric tests are the clue for diagnosis of sudden unilateral loss (so-called neuronitis), whereas they give only complementary information for patients with BPPV. Posturography adds information in all categories concerning the standing position and can be interesting in the scope of rehabilitation treatment. The findings of a retrospective study in patients with BPPV (n = 95), compared with patients with Ménière's disease (n = 89) and others with sudden unilateral loss syndrome (n = 48), illustrate these concepts.