The clinical significance of direction-fixed mono-positional apogeotropic horizontal nystagmus

Objective. A mono-positional persistent, direction-fixed apogeotropic nystagmus (MPosA- poNy) is very challenging for the neuro-otologist. MPosApoNy can be found in patients suffering from a partially compensated acute unilateral vestibulopathy; with a normal ca- loric test, one can speculate the presence of “trapped” otolithic debris located close to the ampulla of the horizontal semicircular canal. Methods. Among 957 patients suffering from vertigo and dizziness, we selected 53 cases of MPosApoNy. Results. In 28 patients, caloric test showed a canal paresis on the same side of the MPosA- poNy. In the remaining 25 cases, MPosApoNy was the only clinical finding. We hypoth- esized the presence of horizonal canal lithiasis and patients were treated with a Gufoni manoeuvre, followed by a forced prolonged position. Conclusions. Performing bedside examination in a patient suffering from vertigo, the pres- ence of MPosApoNy may be due: a) facilitation of a subclinical nystagmus due to the mechanism of apogeotropic reinforcement; b) horizontal canal lithiasis with ‘trapped’ oto- liths close to the ampulla. The disappearance of MPosApoNy following a repositioning manoeuvre or conversion in a typical form of canalolithiasis may represent the best method to confirm this hypothesis.