[Vestibular meanifestations of multiple sclerosis. A new diagnostic element revealed by bithermic tests].

We studied 56 cases of disseminated sclerosis, all during an attack of the disease and all presenting with symptoms of incoordination. The diagnosis was certain both clinically and biochemically. Out of this population, 64% of the patients had unprovoked nystagmus; of these patients 48% had central type nystagmus (multiple, vertical superior or vertical inferior, or bilateral "gaze nystagmus"). We investigated particularly abnormalities in the bithermic tests (vestibular hypovalency, directional preponderance of nystagmus, thermic preponderance) and in particular we studied an index which to the best of our knowledge has never been seriously and statistically investigated. We called this the bithermic reflexogenic index or BRI. We express abnormalities in this index in terms of a disharmony in the bithermic response of one or both vestibules. This index is expressed by the formula o cold + o hot/o cold-o hot x 10 which is the relative difference in the cold and hot test for the same vestibule. The normal index based on research in 180 normal vestibules, is always less than 20. The response is measured in frequency. The results of this study on bithermic tests allowed us to divide our DS population into two main groups: -- the first group comprised 36% of our cases. All the parametric indices are normal (directional preponderance of the nystagmus, thermic preponderance and bithermic reflexogenic index) but the presence of unprovoked nystagmus (88% of the group) is always associated with bilateral vestibular hypereflectivity; -- the second group comprised 64% of the DS patients studied. Unprovoked nystagmus was seen in 50%. All had normal vestibular reflexes or subnormal reflexes without clear cut hypovalency, associated with an abnormality either of directional preponderance of the nystagmus (30%) or of thermic preponderance (25%), or both combined (22%). But in all cases there was an abnormality of the bithermic reflexogenic index greater than 20. This abnormality seems to us to be the most frequent and the most typical. The specificity of this index is under study at the present time. One or another of these syndromes appearing in a young subject who does not have a past medical history of head injury or vascular accidents is strongly in favour of an attack of disseminated sclerosis.