||Jennifer R Evan, MD, Department of Neurology, The Johns Hopkins Hospital; Ari Shemesh, MD, Department of Neurology, The Johns Hopkins Hospital; Daniel R. Gold, DO, Departments of Neurology, Ophthalmology, Neurosurgery, Otolaryngology - Head & Neck Surgery, Emergency Medicine, and Medicine, The Johns Hopkins School of Medicine
||This is a 60-year old man with diabetes presenting with acute onset prolonged vertigo that was ongoing at the time of this examination. Which of the following statements are true with regard to the localization and/or etiology of this patient's symptoms? A. Whether or not symptoms worsen with head movements will reliably distinguish the acute vestibular syndrome (AVS - prolonged vertigo, unsteadiness, nausea/vomiting, spontaneous nystagmus lasting for >24 hours) from benign paroxysmal positional vertigo (BPPV) B. Nystagmus in vestibular neuritis follows an inhibitory pattern, while the nystagmus associated with BPPV follows an excitatory pattern C. Dix-Hallpike testing reliably differentiates BPPV from vestibular neuritis D. Video-Oculography (VOG) and video head impulse testing (vHIT) are necessary to distinguish between BPPV and vestibular neuritis E. This patient has a central cause of the acute vestibular syndrome Answers: A. Incorrect. With any vestibular disorder (the AVS included), nystagmus and vertigo are commonly aggravated by head movements. This must be differentiated by BPPV, where nystagmus and vertigo are triggered by head movements. Ex) performing a Dix-Hallpike maneuver in a patient with vestibular neuritis (the most common cause of the AVS) will increase symptoms, although this does not represent a ‘positive' Dix-Hallpike which would lead to a diagnosis of posterior canal BPPV (accompanied by typical upbeat-torsional nystagmus toward the lowermost or affected ear). B. Correct. Vestibular neuritis is due to acute unilateral vestibular loss, leading to static (spontaneous nystagmus) and dynamic (abnormal head impulse test) semicircular canal asymmetry. In BPPV, the movement of otoconia (following a head movement) within a semicircular canal (usually the posterior canal) causes vestibular excitation. With jerk nystagmus, the slow phase represents the pathologic phase - i.e., with vestibular neuritis, the process is inhibitory and the slow phase will be towards the paretic ear (e.g., right vestibular neuritis - inhibition/decrease firing of the right 8th cranial nerve leads to unopposed left semicircular canal afferents, with slow phase drift to the right ear, fast phase is left-beating), while in BPPV, the slow phase is generated by excitation (e.g., right posterior canal [PC] BPPV - stimulating the right PC leads to a slow phase downward and torsional phase toward the left ear, and the fast [named] phase of nystagmus will be upbeat and torsional toward the right ear). Features of nystagmus due to BPPV include: a short latency between Dix-Hallpike and nystagmus, limited duration of <30-60 seconds, and fatiguability on repeated testing. In lateral or horizontal canal BPPV, the nystagmus is horizontal and will change direction depending on the side to the which the head is moved with the supine roll test: e.g., geotropic nystagmus will be right-beating with right ear down and left-beating with left ear down while apogeotropic nystagmus will be right-beating with left ear down and left-beating with right ear down. C. Incorrect. Dix-Hallpike is rarely helpful in a patient with the acute vestibular syndrome, aside from intensifying vestibular symptoms and nystagmus. Dix-Hallpike is the diagnostic test of choice for posterior canal BPPV. Patients with lateral/horizontal canal BPPV are better tested with supine roll test than Dix-Hallpike, although it is common for at least some horizontal nystagmus to be seen with Dix-Hallpike when dealing with the horizontal canal variant. Patients with the AVS, which includes mainly vestibular neuritis and stroke, should be diagnosed and triaged using the three step ocular motor ‘HINTS' exam, which stands for Head Impulse, Nystagmus, Test of Skew. The Dix-Hallpike maneuver is not helpful diagnostically in a patient with the AVS, and the HINTS exam is not helpful diagnostically in a patient with BPPV. That being said, there is a role for Dix-Hallpike in patients who suffered from vestibular neuritis, who then experience typical positional symptoms consistent with BPPV. Although there is a loss of vestibular function following neuritis, the superior division (innervates the anterior, horizontal canals, utricle, and small contribution to saccule innervation) may be preferentially affected, while the inferior division (innervates the posterior canal and saccule) may be preferentially spared. The exact mechanism is unclear, although theories have centered around possible dislodgement of otoconia from the damaged utricle (which may then enter the ipsilateral posterior canal), or this may result from the patient preferring to lie on the affected (ipsilesional) side to minimize symptoms of vestibular neuritis. Regardless of the exact mechanism, post-vestibular neuritis ipsilesional PC-BPPV will similarly respond to Epley or Semont maneuvers. D. Incorrect. VOG allows nystagmus and the head impulse test to be recorded and quantified, although the bedside exam is sufficient to establish diagnoses of BPPV or vestibular neuritis vs stroke in the AVS in the vast majority of cases. However, the clinician should understand the rationale for the Dix-Hallpike and HINTS exams, and the appropriate clinical situations in which each should be applied. In this patient, the abnormal bedside HIT to the right is not so apparent in the video, and is more clearly demonstrated when analyzing the vHIT traces. Not only can the corrective overt saccades (those visible on the bedside exam) be visualized on the vHIT, but also the corrective covert saccades (those not visible on the bedside exam that occur during head movements, and represent a presumed compensatory mechanism) and gain (ratio of output [eye movement velocity] to input [head movement velocity]). In this case, gain is <0.7, which is considered abnormal and this patient's unilateral vestibular loss is on the right side which would be expected given spontaneous left-beating nystagmus. E. Incorrect. This patient has unidirectional left-beating nystagmus, an abnormal HIT to the right, and no skew deviation (in the video, an exophoria can be seen - however, this is a horizontal ocular misalignment so does not represent a skew deviation) and there was no acute hearing loss; therefore, he was diagnosed with right vestibular neuritis. Discussion: The acute vestibular syndrome (AVS) is described as the rapid onset (over seconds to hours) of vertigo, nausea/vomiting, and gait unsteadiness in association with head-motion intolerance and nystagmus, lasting days to weeks. In the emergency setting, the evaluation focuses on ruling out a central cause such as a stroke. It has been shown that, in the AVS, the HINTS exam is superior to MR with diffusion-weighted imaging for detecting stroke and other central causes in the first 24-48 hours. An exam such as this patient's is considered ‘peripheral', and in his case, the etiology of his AVS was right-sided vestibular neuritis. Peripheral findings included: unidirectional (contralesional) left-beating nystagmus that follows Alexander's law (nystagmus increases in the direction of the fast phase); abnormal (ipsilesional) head impulse test to the right; absence of skew deviation with alternate cover testing; and lack of other cranial neuropathies or neurologic symptoms/signs. In his case, there was no hearing loss on the right side, which is important in the distinction of whether the ‘peripheral' etiology is benign and due to vestibular neuritis (hearing spared) or whether the ‘peripheral' etiology could represent a dangerous etiology like labyrinthine ischemia (via vascular disease involving the basilar, anterior inferior cerebellar or internal auditory arteries). The HINTS ‘Plus' exam - adding a test of finger rub at the bedside and inquiring about new hearing loss - raises the sensitivity to detect a stroke (i.e., capturing labyrinthine ischemia which almost always involves the cochlea) from the 3-step HINTS exam, while slightly reducing the specificity of the exam (i.e., some cases of infectious labyrinthitis, which is a benign cause of hearing loss, may be imaged unnecessarily). With regard to BPPV, the posterior canal accounts for the vast majority of cases (~80-90% of cases), while lateral/horizontal canal BPPV is the next most common location (~10-20% of cases). The anterior canal (AC) is rarely involved given its orientation relative to gravity, which usually prevents otoconia from entering. When downbeat or downbeat-torsional nystagmus is triggered by the Dix-Hallpike maneuver, this could theoretically represent AC-BPPV, but might also represent PC-BPPV where the otoconia flow in an inhibitory direction or could represent a central etiology (e.g., cervicomedullary lesion). The Dix-Hallpike test is the test of choice to detect posterior canal BPPV, while the supine-roll test is the test of choice to detect lateral or horizontal canal BPPV. The Epley or Semont maneuver treats posterior canal BPPV, while the BBQ roll, Gufoni and others are commonly used for horizontal canal BPPV.