Medical Excellence- Issue 1

deviation or HINTS—head impulse, nystagmus, test of skew. Another study showed similar accuracy when performed by stroke neurologists [57]. Preliminary evidence suggests that “spe- cially trained” emergency physicians can learn to use nystagmus and head impulse testing [58, 59]. My own anecdotal experience also suggests that with some training, emergency physicians can perform and interpret this examination. However, because this approach has not been fully validated when used by nonspecial- ists, I have added two additional components that should be a part of the basic evaluation of the acutely dizzy patient anyway— the general neurological examination and testing of gait. I do not perform these tests in the order of the HINTS mne- monic but rather in the following order: 1. Nystagmus testing 2. Skew deviation 3. Head impulse testing (HIT) 4. General neurological exam, focusing on cranial nerves in- cluding hearing, cerebellar testing, and long-tract signs 5. Gait testing There are two reasons for this sequence. Firstly, I like to start with the least “intrusive” parts of the examination, and, secondly, nystagmus testing is the component that helps the most, in part by its presence or absence and in part by its quality. Once any one component tests “positive” for a central cause, then the patient’s disposition (admission for further neurological evaluation) is clear. Although all five components mentioned above are part of a complete examination for a patient with an AVS, causing the patient to feel worse with further intrusive testing (e.g., testing gait that provokes vomiting) after a less intrusive test is posi- tive will not change the disposition and just result in the patient feeling worse. Furthermore, nystagmus helps to anchor and inform the rest of the process. Essentially all patients with an AVS due to vestibular neuritis will have nystagmus if examined within the first days, so its absence should make one question the diagnosis. To be sure that nystagmus is truly absent, it should be tested with visual fixation removed. Experts state that the absence of nys- tagmus in a patient examined with their visual fixation removed essentially rules out a vestibular cause for the dizziness [60]. Subspecialists typically use Frenzel lenses to remove visual fixa- tion, neither available nor common practice in emergency medi- cine practice. A simple solution is to take a large piece of white paper, place it close to the patient’s eyes (telling them to “look through the paper”), and examine the nystagmus from the side. This technique is only needed if there is no nystagmus with the basic exam. If nystagmus is truly absent, then this is unlikely to be a vestibular process, and therefore head impulse test is not useful and may yield false information. It is still important to perform a complete neurological exam with special attention to brainstem and cerebellar function and gait since patients with cerebellar stroke often do not have nystagmus. The degree (or amplitude) of nystagmus can fluctuate mark- edly even over hours. This may represent the natural history of the underlying pathology as the CNS accommodates to the ab- normal physiology from vestibular neuritis or from medications (e.g., ondansetron or a benzodiazepine) that are often appropri- ately used in the ED to reduce symptoms but may accelerate the rate at which the nystagmus dampens. Nevertheless, clinical testing for nystagmus is quite simple. Have the patient look straight ahead in “neutral” or “primary” gaze and observe for eye movements. By convention, the direc- tion of nystagmus is named by the direction of the fast com- ponent. With minimal practice this is easy to see and describe. Importantly, it is the details of the nystagmus, not simply its pres- ence that is most diagnostically important. After observing for nystagmus in primary gaze, test for “gaze-evoked” nystagmus by having the patient look to the right and then to the left, each for several seconds, and observe for the presence of nystagmus and the direction of its fast-beating component. The patient only needs to move their eyes 20–30° off-center when testing for gaze-evoked nystagmus because many normal individuals will have a few beats of horizontal nystagmus on full end gaze. This physiologic nystagmus is generally very low amplitude and ex- tinguishes quickly. Table 4 shows the typical findings for patients with the ocular motor examination for patients with the AVS. Direction-changing gaze-evoked nystagmus or nystagmus that is pure torsional or vertical is central in origin (in the setting of an AVS, a stroke). Skew deviation (a vertical misalignment of the eyes due to imbalance in the gravity-sensing pathways) is not very sensitive (30%) but is very specific (98%) for a brain stem lesion [42]. For this examination, the examiner uses the “alternate cover” test. With the patient looking directly at the examiner’s nose, the physician alternately covers the right eye and then the left eye and continues alternating back and forth, approximately every 2 s. In patients with skew deviation, each time the covered eye is uncovered, there will be a slight vertical correction (one side cor- rects upward and the other corrects downward). The amplitude of correction is small, 1–2 mm; therefore, it is key for the exam- iner to focus on one eye (either one), rather than following the uncovered eye. A normal response is no vertical correction, and an abnormal response should be considered a stroke in patients with an AVS. The next component is the HIT, a test of the vestibulo- ocular reflex (VOR), only described in 1988 [61]. Standing in front of the patient, the examiner holds the patient’s head by each side and instructs the patient to maintain their focus on the examiner’s Issue-1  |  7 MEDICAL EXCELLENCE