Hyperventilation-Induced Nystagmus in Acute Unilateral Vestibulopathy: A Correlation with Vestibulo-ocular Reflex Gain and Clinical Implication.

Hyperventilation-induced nystagmus test (HINT) is capable of generating a response in 77.2% of cases of acute unilateral vestibulopathy (AUVP); both nystagmus toward the affected side (excitatory pattern) and toward the healthy side (inhibitory pattern) have been described. The aim of the study is to investigate the clinical and prognostic role of the test by evaluating its correlation with vestibulo-ocular reflex (VOR) gain. We evaluated 33 AUVP patients by performing the HINT and video head impulse test (V-HIT) during the acute phase and then at 15 and 90 days after the onset of the symptoms. The correlation between the VOR gain of the affected side and test responses was evaluated first, phase by phase, and then considering the pattern shown during the first assessments. Patients with a negative HINT had a higher mean VOR gain than patients with a positive test at both 15 and 90 days. Patients who showed an inhibitory pattern at the first assessment had a continuous improvement in V-HIT performance, while patients with an initial excitatory response had a transient decrease in gain at the subsequent evaluation (P=.001). No difference between these 2 groups emerged at 90 days (P=.09). The finding of a negative HINT during the follow-up correlates with good V-HIT performance and could be an indicator of good recovery. The inhibitory pattern is associated with a subsequent improvement; and it would be indicative of compensation. but, despite this, the prognostic value of the test is limited.