Uphill/downhill nystagmus

Differential diagnosis between peripheral and central spontaneous nystagmus can be difficult to classify (as peripheral or central) even on the basis of criteria recommended in the recent literature. The aim of this paper is to use the combination of spontaneous nystagmus and ocular tilt reaction to determine the site of origin of the disease that causes nystagmus. We propose to classify the nystagmus in: 1) "Uphill" nystagmus in which the nystagmus takes on an inclined plane and the direction of the fast phase is towards the hypertropic eye (this type of nystagmus is likely peripheral); 2) "Downhill" nystagmus when the nystagmus beats toward the hypotropic eye (this type of nystagmus is likely central); 3) "Flat" nystagmus when the plane on which nystagmus beats is perfectly horizontal: in this case, we cannot say anything about the site of lesion (it was only detected in 15% of cases). The spatial position of nystagmus vector has to be considered as an intrinsic characteristic of the nystagmus itself (as direction, frequency, angular velocity etc.) and must be reported in the description, possibly giving an indication of the site of damage (peripheral or central). In particular, similar results are obtained by comparing the inclination of the nystagmus with the head impulse test (HIT, considered the best bedside test now available). It seems that this sign may confirm HIT for safer diagnosis or replace it in case of doubt. In contrast, in case of "Flat" nystagmus (probably attributable to the fact that the utricular maculae are spared), HIT can replace observation of the plane of the nystagmus. Thus, the two signs confirm and integrate each other. The test does not require additional time and is not tedious for the patient. It is proposed that it be included in the evaluation of spontaneous nystagmus in everyday clinical practice.