2431 Predictive acute nystagmus characteristics in posterior circulation stroke diagnosis

ObjectivesThe acute nystagmus characteristics of posterior circulation stroke (PCS) were assessed and compared to acute vestibular neuritis (AVN) in the emergency department (ED)MethodsVideo-nystagmography (VNG) was prospectively conducted in ED at one Australian metropolitan tertiary referral hospital over a three-year period, recording ictal nystagmus in 101 patients with radiologically confirmed PCS and 104 patients with AVN.ResultsPCS locations were in the brainstem alone (34.7%), cerebellum alone (29.7%), both cerebellum and brainstem (19.8%) or other/multiple locations (15.8%) were recruited. Common PCS territories included: posterior-inferior-cerebellar-artery (38.6%), multiple-territories (20.8%), pontine-perforators (18.8%), anterior-inferior-cerebellar-artery (6.9%) and posterior-cerebral-artery (5.9%).In PCS, 50.5% of patients had no spontaneous nystagmus. Remaining PCS patients had primary position horizontal (37.2%), vertical (8.9%) and torsional (3.9%) nystagmus. Horizontal nystagmus was 51.7% ipsiversive and 48.3% contraversive in 29 lateralised PCS. 28.4% of PCS patients had pathologic gaze-evoked nystagmus. Most PCS patients with horizontal nystagmus (60.5%) had unidirectional ‘peripheral-appearing’ nystagmusIn contrast, AVN patients almost universally (98.1%) had primary position horizontal nystagmus. No AVN patient had gaze-evoked nystagmus. Horizontal nystagmus with SPV≥5.4 /s distinguished AVN from PCS with sensitivity and specificity of 90.3% and 89.1%.Absent nystagmus, gaze-evoked direction-changing nystagmus, and vertical/torsional nystagmus were all highly specific for PCS (100%, 100% and 98.1%).ConclusionMost patients with PCS had concerningly benign features such as absent nystagmus or unidirectional ‘peripheral-appearing’ horizontal nystagmus acutely. Comparatively, all AVN patients had nystagmus acutely. This study reinforces a new paradigm in vestibular neurology that absence of findings does not equate to absence of pathology.