Oculomotor Profile in Acute Vestibular Syndrome - Value of Saccades, Pursuit Eye Movements and Pupillary Reflexes in Differentiating Central and Peripheral Causes

A chief complaint of acute vertigo or dizziness is related to about 2.1 to 7.1% of all emergency department (ED) visits, translating to about 4.3 million ED visits in the USA per year. With the differential diagnosis of patients presenting with acute or episodic vertigo / dizziness being very broad and cutting across all specialties, frontline providers and specialists may be overwhelmed by the approach to this symptom. In patients presenting to the ED with vestibular symptoms, life-threatening conditions have been identified in a single study in 23.8% of visits, with 12.5% of all visits related to cerebrovascular events. This emphasizes the need to distinguish between dangerous central and benign, self-limited peripheral vestibular disorders to avoid misdiagnosis. Patients with an acute vestibular syndrome (AVS) have acute-onset, continuous vertigo, dizziness, or unsteadiness lasting days to weeks, usually associated with vomiting, nystagmus, severe postural instability and head movement intolerance . Both patients with stroke and vestibular neuritis can present with an AVS. Approximately 25%±15% of AVS patients will be diagnosed with a stroke, usually in the posterior circulation. Established diagnostic workup in the ED include neurologic assessment, followed usually by CT-based imaging of the brain. Often neurology consultations will be ordered.

For posterior circulation strokes presenting with dizziness frontline misdiagnosis appears common, occurring in roughly 35% of cases. The desire to avoid missing a stroke often triggers brain imaging (computed tomography [CT] and magnetic resonance imaging including diffusion-weighted imaging [MRI-DWI]), laboratory workup and/or electrocardiography. Unfortunately, a recent meta-analysis found that the sensitivity of CT for central causes of dizziness was only 28.5%. Even MRI-DWI in AVS has limited sensitivity, missing about 1 out of 5 vertebrobasilar strokes presenting as an AVS when obtained within the first 24-48 hours after symptom onset. If stroke, the most common central cause of the AVS is missed or delayed, the underlying stroke mechanism goes untreated sometimes resulting in extension of the original infarct or development of a new, larger one.

The evidence base for effective bedside differentiation of inner ear diseases from stroke in patients with acute dizziness and vertigo has grown substantially over time, as emphasized recently. Although useful if present, obvious focal neurologic signs only have a sensitivity of 44% for detecting a central cause of AVS, i.e., more than 50% of strokes will be missed if one were to rely on these findings. Thus, different clinical strategies that emphasize the combined use of targeted neuro-otologic bedside examination techniques, such as the HINTS (Head Impulse, Nystagmus, Test of Skew), HINTS+ (which adds a bedside test of hearing), STANDING or gait/truncal instability (GTI) assessment have been proposed.

Both the HINTS(+) exam and the STANDING algorithm are very good exclusion tests in the hands of trained emergency physicians, non-sub-specialists and neuro-otology / neuro-ophthalmology subspecialists. Ideally, HINTS+ are combined with a graded GTI rating or the STANDING algorithm is used instead. However, absent or inadequate training in performing and interpreting subtle oculomotor findings constitute important limitations, especially in frontline providers. Most ED physicians are not yet familiar with a structured approach to the dizzy patient as e.g. outlined in the TiTrATE approach and HINTS(+) or similar bedside algorithms. While the introduction of quantitative (video oculography - VOG) HINTS to the ED seems promising, increasing the diagnostic accuracy beyond that of neuro-otology experts, this concept is far from being implemented broadly in routine emergency medicine practice.

This emphasizes the need to further improve the approach to the acutely dizzy patient now, focusing on bedside testing that can be reliably applied by untrained frontline providers including emergency physicians or neurology residents also. Brainstem and cerebellar loss of function have been demonstrated to result in dysmetric saccades and saccadic pursuit eye movements. In a previous study, vertical pursuit was saccadic significantly more often in central AVS patients than in peripheral AVS patients (88% vs. 20%, p<0.01). In patients with (dorso)lateral medullary lesions or carotid artery dissection, pupillary abnormalities (Horner syndrome) may be noticed and in midbrain lesions an unilaterally dilated pupil (as part of a third nerve palsy) may be observed, whereas for other acute brainstem or for cerebellar lesions little is known about pupillomotor changes. Testing for both saccadic eye movements (SEM), pursuit eye movements (PEM) and pupillary responses is straight-forward and readily applicable by frontline providers.