The Predictive Role of Video Head Impulse Testing Patterns of Anti-Compensatory Saccades Using the Suppression Head Impulse Paradigm for the Diagnosis of Mild Acute Unilateral Vestibular Loss

<b>Background/Objectives:</b> To evaluate the predictive role of anti-compensatory saccades in diagnosing mild acute unilateral vestibular loss. <b>Methods:</b> Consecutive patients with vertigo who underwent a bedside vestibular evaluation and video head impulse testing of the horizontal semicircular canal at the San Bernardino Outpatient Clinic in Salò, Italy, between 1 January and 30 June 2024 were examined (Group 1). Two control groups were considered: patients with severe unilateral acute vestibular loss (Group 2) and healthy subjects (Group 3). The video head impulse testing patterns of anti-compensatory saccades (amplitude, scattered pattern, and latency) using the suppression head impulse paradigm were analyzed to evaluate their predictive role in identifying horizontal canal dysfunction, even when borderline gain values of the canal's vestibulo-ocular reflex were present. <b>Results:</b> Group 1 included 74 patients, Group 2 included 20 patients, and Group 3 included 20 healthy, voluntary subjects. The anti-compensatory saccades revealed significant differences in the amplitudes and scattered patterns between the two ears, exclusively in Groups 1 and 2. <b>Conclusions:</b> The anti-compensatory saccades alterations using the suppression head impulse paradigm can predict mild acute unilateral vestibular loss, even when the horizontal semicircular canal's vestibulo-ocular reflex gain values are mild (lower borderline). Conversely, a borderline asymmetry of the horizontal semicircular canal's vestibulo-ocular reflex using the classic head impulse paradigm should not be considered a marker of mild acute unilateral vestibular loss when the saccadic pattern is symmetrical using the suppression head impulse paradigm. Further meticulous differential diagnostic investigations are necessary in such cases to effectively diagnose horizontal semicircular canal dysfunction.