Vestibular Neuritis with + Head Impulse Test and Unidirectional Nystagmus

Vestibular neuritis is the most common cause of the acute vestibular syndrome, which is characterized by continuous vertigo and spontaneous nystagmus lasting days. It may be mimicked by central causes, including stroke, but in the hands of subspecialists, the HINTS+ (Head Impulse, Nystagmus, Test of Skew, where + is the addition of a bedside finger rub assessment of hearing) examination can detect a central cause of the acute vestibular syndrome with a very high sensitivity and specificity (both >95%). In this patient's case, her left-beating nystagmus and + head impulse test to the right (a catch-up saccade can be seen as her head is moved quickly to the right - her eyes move with the head to the right for a split second given loss of the vestibulo-ocular reflex, and there is a catch-up saccade back to the left so she can refixate on the target) are both explained by acute loss of vestibular function on the right side (right sided vestibular neuritis). As the vestibular neuritis decreases the baseline tonic activity of the affected (right) 8th cranial nerve, there is relative hyperactivity involving the left 8th cranial nerve, which leads to the false perception of leftward head turning. In response, rightward slow phases are generated, which represents the slow (pathologic) phase of her nystagmus. The rightward fast phase is the position reset mechanism and creates the rhythmic slow and fast phases. Her left-beating nystagmus (LBN) is unidirectional - i.e., it remains LB in all directions of gaze - and follows Alexander's law where the nystagmus increases in intensity in the direction of the fast phase (to the left in this case). If unidirectional nystagmus is seen beating to the left, a + head impulse to the right must be seen to reassure the clinician that this is a peripheral etiology. Additionally, a skew deviation must be absent, and unilateral hearing loss (ipsilateral to the side of the unilateral vestibular loss) should be absent. When acute unilateral hearing loss is present, labyrinthine ischemia should be considered, which is the rationale for the 4 step HINTS+ exam. ; ; In vestibular neuritis the symptomatic course is typically self-limited, due to central compensatory mechanisms, most of which occur at the level of the vestibular nuclei. Spontaneous nystagmus improves and resolves over days-weeks depending on the severity of the injury. Similar to optic neuritis, steroids may hasten recovery, but there's no clear clinical evidence to suggest that it influences the final outcome. Vestibular suppressant medications shouldn't be used for more than a few days as they reduce vestibular asymmetry thus delaying normal adaptive mechanisms. Patients should undergo vestibular physical therapy to help optimize their vestibular recovery and compensation using other sensory modalities (e.g., vision and proprioception). [[[SEE FIGURE 1 - CLICK HERE: https://collections.lib.utah.edu/details?id=1278692 The video head impulse test (vHIT) is a technique used to quantify the bedside head impulse test. This vHIT was performed 2 weeks after her presentation to the emergency department (seen in the video), and given normal horizontal canal vestibulo-ocular reflex (VOR) function on the left side, a HIT directed to the left side produces a gain within the normal range (defined as >0.7). Since stimulation of the left horizontal canal produces rightward eye movements (via the VOR) whose velocities approximate the velocities of the head movements - if the head and eye velocities match up perfectly, the gain is calculated as 1.0. In this patient's case, when the head is moved quickly to the right, given the loss of horizontal canal function on the right side (due to right sided vestibular neuritis), the velocity of the eye movements directed to the left side (seen in green) are much lower than the velocity of the head movement, which results in a low gain of 0.35 with significant asymmetry between the two sides (53%). Additionally, compensatory "catch-up" saccades are seen in red following HIT to the right - those that occur with the head movements are referred to as covert saccades and may be missed with the bedside HIT, and those occurring after the head movement are referred to as overt saccades, and these are the visible catch-up saccades seen at the bedside (and in the video). Covert saccades commonly develop over time and are thought to be compensatory. This is a patient with a "peripheral" HINTS exam consistent with vestibular neuritis on the right side.]]]