Subjective visual vertical (SVV) assessment using the bucket test is clinically useful in distinguishing central vestibular disorder (CVD) from vestibular migraine (VM), according to a study published in BMC Neurology.
To identify any combination of neuro-vestibular bedside examinations that might improve the sensitivity and specificity to distinguish CVD from VM, researchers examined symptomatic patients with CVD (n=27) or VM (n=36) between January 1, 2013, and December 31, 2013. Age- and sex-matched nonsymptomatic participants with CVD were also recruited (n=27). The structured clinical examination for each patient included SVV using the bucket test; age, blood pressure, clinical features, duration of symptoms (ABCD²); headache and vertigo history; formal neurological examination; video-oculography examination for spontaneous, gaze-evoked, positional, and head shaking–induced nystagmus; and clinical head impulse testing.
The abnormal rate of SVV deviation in the CVD group was significantly higher than that of the VM group (74.1% vs 8.3%; Chi-Square test; P <.001). Sensitivity and specificity with use of the bucket test alone to differentiate CVD from VM were 74.1% and 91.7%, respectively. Compared with other diagnostic tests, SVV was the most sensitive (McNemar test; P <.05) but not the most specific.
Limitations of this study include a potential underestimation of abnormal SVV deviations, focal neurological signs, or nystagmus, due to possible changes between onset and examination in the asymmetrical resting firing rates of each vestibular system that cause vertigo and the associated signs. This is unlikely to have had a significant impact, however, given that patients were symptomatic during clinical assessment. Additionally, the duration between vertigo onset and examination was different between the CVD and VM groups. However, despite a longer interval to examination, patients in the CVD group had higher rates of abnormal SVV deviations, abnormal nystagmus, and positive focal neurological signs compared with patients in the VM group.
“The combined clinical findings of perception of a tilted vertical (SVV bucket test > 2.3°), a positive neurological exam, and gaze stability being abnormal (spontaneous or gaze-evoked nystagmus with visual fixation) has high sensitivity and specificity to distinguish CVD from VM,” concluded the researchers. “In the case of acute vertigo presentations, the [Head Impulse, Nystagmus, and Test of Skew] HINTS examination remains the most important tool for distinguishing central from peripheral causes. However, in the case of a normal head impulse test, a pathophysiological reason such as VM may be the cause — in which case the diagnostic battery combining bucket test, focal neurological signs and nystagmus is very useful.”
Chang TP, Winnick AA, Hsu YC, Sung PY, Schubert MC. The bucket test differentiates patients with MRI confirmed brainstem/cerebellar lesions from patients having migraine and dizziness alone [published online September 3, 2019]. BMC Neurology. doi: 10.1186/s12883-019-1442-z