Acute Imbalance Syndrome vs Acute Vestibular Syndrome

BACKGROUND AND OBJECTIVES: Stroke is a major differential diagnosis in patients with acute vertigo/dizziness or imbalance. Current diagnostic algorithms such as head impulse test, gaze-evoked nystagmus, and test of skew are optimized for presentations with spontaneous nystagmus (SPN), traditionally called acute vestibular syndrome (AVS). However, in recent studies, a relevant proportion of patients with stroke-related vertigo/dizziness had no SPN, but rather postural or gait imbalance, a phenotype lately termed acute imbalance syndrome (AIS). We aimed to outline the pathoanatomical differences of stroke-related AIS vs AVS and its clinical implications. METHODS: Patients with MRI-proven stroke-related acute vertigo/dizziness or imbalance were included in this emergency department (ED) cohort study at LMU Hospital prospectively. Vestibular, ocular motor, and postural signs were documented (including SPN presence/intensity by video oculography, postural imbalance by posturography). Patients were classified as suffering from AIS or AVS based on the presence of SPN. Stroke lesion distribution was depicted in Montreal Neurological Institute space and supplemented by structural disconnectome mapping from the lesion cores. Multivariate lesion symptom-mapping based on support-vector regression and disconnectome mapping was applied for SPN intensity and sway path as surrogate markers for AVS and AIS. RESULTS: Of 75 patients (age: 65.7 ± 13.3 years, 40% female), 58.7% were diagnosed with AIS, 38.7% with AVS, and 2.7% with central positional vertigo. In AIS, the lesion core was located in the anterior cerebellar lobe and deep cerebellar nuclei (superior cerebellar artery/posterior inferior cerebellar artery territory) connecting to the bilateral pontomesencephalic tegmentum through the superior cerebellar peduncle. AVS stroke lesions were mostly located in the posterior cerebellar/flocculonodular lobe (posterior inferior cerebellar artery/anterior inferior cerebellar artery territory) and connected to the ipsilesional vestibular nucleus (VN) and bilateral medial longitudinal fascicle (MLF) through the inferior cerebellar peduncle. SPN intensity correlated with voxels in the cerebellar lobules VI-IX connecting to VN and MLF. Postural sway was associated with a small local cluster in the cerebellar Crus I. DISCUSSION: AIS accounts for more than half of patients with stroke-related vertigo/dizziness or imbalance. AIS lesions were located in the anterior cerebellar lobe, disturbing cerebellar-pontomesencephalic networks for posture and gait control. AVS lesions affected the posterior cerebellar/flocculonodular lobe and associated vestibulo-ocular reflex networks. Recognition of both clinical phenotypes is essential to identify all strokes among patients with vertigo/dizziness in the emergency setting. TRIAL REGISTRATION INFORMATION: DRKS00008992; U1111-1172-8719.