There exist 3 common possibilities for direction-changing geotropic nystagmus induced by a change in head position; these are benign paroxysmal positional vertigo (BPPV), migraine, and “light cupula.” BPPV affecting the horizontal semicircular canal (hSCC) is not as uncommon as earlier estimates. Larger sample size studies (n > 200) investigating the incidence of horizontal canal BPPV (verified from nystagmus recording or observation) confirm BPPV affects the hSCC from 10% to 31%.1–3 Geotropic hSCC-BPPV is characterized by a fatiguing nystagmus that beats toward the ear that is closest to earth when the head/body is positioned in side-lying.4,5 This nystagmus is believed to be caused by free-floating otoconia inside the endolymph of the hSCC and is termed canalithiasis.5,6 In canalithiasis, the geotropic nystagmus velocity consists of a crescendo-decrescendo profile and typically resolves within 60 seconds. Those patients in whom nystagmus is accompanied by confirmed migraine have been shown to have a persistent geotropic direction-changing nystagmus, yet the duration tends to persist well beyond 60 seconds and the velocities tend to be slower.7
Recently, persistent geotropic nystagmus has been described in the literature and presumed due to a “light cupula.”8 The light cupula (LC) theory suggests that nonfatiguing geotropic nystagmus has no latency, persists for greater than 1 minute, and a null point can be identified.9 The null point refers to a supine head position, rotated in yaw, which causes the horizontal nystagmus and vertigo to stop, typically when the head is rotated 40° (on average) toward the affected ear.9 The null point can help identify the side of the lesion in LC. In addition, positioning the head into flexion or extension may also aid in diagnosing the affected LC.10 Positioning the patient in side-lying causes the “lighter” cupula to be deflected away from the ground, thereby generating the geotropic nystagmus. One study has demonstrated an incidence of LC of 4.9% among patients incorrectly diagnosed with BPPV and 14.2% in patients presenting with geotropic, direction-changing positional nystagmus.11 LC is theorized to be caused by a cupula with a lower specific gravity than the surrounding endolymph.8,9,11 It has also been suggested that the positional nystagmus because of the LC reverses in the prone position.12 The use of canalith repositioning maneuvers (CRM) has not been found to be useful in treating LC. At 1 week, 74% of patients with LC were free of nystagmus and vertigo, and the resolution of symptoms was presumed to spontaneous.11
The oculomotor examination and gait presentation are critical to distinguish central from peripheral vestibular causes of direction-changing nystagmus and vertigo. The clinical examination should consist of head impulse test, an examination of nystagmus, test of skew, and lateropulsion, which have been shown to be more sensitive than imaging for distinguishing an acute vestibular crisis.13,14 Using these tests, central pathology is considered when the impulse test is normal, the patient has a direction-changing gaze-evoked nystagmus in head up (neutral) position, a vertical deviation of 1 eye relative to the other (abnormal skew), and has ataxia or a lateropulsion of gait or posture.
Here, we present a complex case involving a high-velocity, nonfatiguing geotropic nystagmus that did not clearly follow the typical clinical rules for hSCC BPPV, migraine, or LC. The history and clinical findings were unlikely due to central pathology on the basis of clinical examination, although the test for skew deviation was not performed.
A 67-year-old man presented to vestibular physical therapy with a diagnosis of vertigo, referred by his primary care physician. He reported vertigo starting 1 week before the date of the evaluation. He rated his vertigo as ranging from 1 to 9 (0-10 scale, with 10 being severe) on the basis of head position. Head positions that increased his vertigo included lying down, rapid head turns, rolling over in bed, and tilting his head down to read. He had not fallen in the past 6 months, but once the episodes of vertigo had started he reported experiencing imbalance walking in the dark. In addition to the vertigo, the patient further experienced mild nausea. When they occurred, the imbalance, vertigo, and nausea lasted from seconds to minutes. He rated the Dizziness Handicap Inventory (DHI) a 32 out 100 (moderate perception of handicap because of dizziness) and his Activities-specific Balance Confidence (ABC) scale rated at 92% (0-100, with 100 suggesting complete balance confidence doing activities).15–17
The patient reported that, in the past, he had experienced lightheadedness related to blood pressure fluctuations with positional changes, but describes the more recent episode of vertigo as severe both at rest and with positional changes. The patient reported normal hearing. His vision was corrected with progressive lenses, but noted it was now somewhat “blurred since the onset of vertigo.” The patient walked to clinic independently, worked full-time as a business consultant, and enjoyed jogging, tennis, and swimming. His medical history included hypertension and atherosclerosis with stent placement in 2011. Medications included Niaspan, Lipitor, Plavix, Norvasc, Coreg, low-dose aspirin, Co Q-10, glucosamine sulfate, and vitamin B complex. His blood pressure was 165/75 in sitting. There was no history for migraine, neither did he meet any of the criteria for vestibular migraine as specified by Lempert et al.18 The patient provided a signed consent (dated August 10, 2014) and the University of Pittsburgh Biomedical Institutional Review Board declared that institutional review board approval was not required.
The patient's gait revealed no lateropulsion. His oculomotor examination was normal for smooth pursuit and saccade testing. Spontaneous and gaze-evoked testing was normal in both room light and with fixation removed. Head impulse and head-shaking nystagmus tests were not completed at the initial visit. Fixation-blocked oculomotor and positional tests were performed using videonystagmography (Interacoustics, Denmark). Right and left Dix-Hallpike tests (DHTs) were performed19 and elicited nonfatiguing, sustained geotropic (horizontal) nystagmus with report of vertigo. The geotropic nystagmus had no latency and was more intense in the left DHT (peak 41°/s). The patient was unable to discern which DHT (right vs left) created a greater intensity of vertigo (Figure 1).
Following the DHT procedure, the patient was positioned in supine in preparation for the supine roll test. In supine he had a right-beating nystagmus (∼3°/s, supine positioning test). During the supine roll test, he developed a nonfatiguing, persistent geotropic nystagmus of greater velocity in right roll (peak 74°/s) compared with that in left roll (peak 62°/s), suggesting right horizontal canal canalithiasis with an atypical duration (Figure 2) or perhaps LC of the left hSCC. The clinician paused the head position at neutral between right and left roll. The supine roll test was repeated and the nystagmus did not fatigue20 or change pattern. The geotropic nystagmus was triggered immediately upon position change (zero latency). The patient reported feeling more severe vertigo in right roll. Null point determination was not performed.
On the basis of the roll test and the subjective report, the clinician elected to treat the patient twice using the 270° roll CRM for right horizontal canal canalithiasis. This option was chosen even though the nystagmus did not clearly indicate this maneuver, by rolling away from the right side in four 90° segments.5 As the patient rolled into prone position from left side-lying, the nystagmus reversed from left beating to right beating; however, this right-beating nystagmus was not different from the direction of nystagmus observed in supine, contrary to what has typically been described in LC.11 Similar responses have been suggested to occur in LC.11 The nystagmus did not cease in prone position as occurs in the successful treatment for canalithiasis of the hSCC. Upon repeat roll testing, the nystagmus and vertigo were still present and intense with no fatigue noted. The patient was given instructions to avoid the supine position for the remainder of the day only, and to continue with his normal activities. At nighttime, he was instructed to sleep in his typical, comfortable position.
At the 1-week follow-up, the patient reported that his dizziness was improved. His DHI score was 4/100 and ABC rated at 98%. He had no evidence of geotropic nystagmus in either the Dix-Hallpike or the roll test positions (Figure 3). The head impulse and head-shaking nystagmus tests were normal. The patient was educated about the possible recurrence of BPPV, instructed to return to the clinic if symptoms recurred, and was discharged from vestibular physical therapy.
Approximately 20 months later, this patient experienced a recurrence of vertigo. The patient reported that his symptoms were similar and noticed vertigo when rolling over in bed and when bending over. Since the prior episode of vestibular physical therapy, he had undergone a left total hip replacement. His DHI had worsened to 38/100 and his ABC was similarly worse, now rated at 59%. He rated his vertigo as ranging from 0 to 6 out of 10 over the past week. His oculomotor examination in room light and with fixation removed was normal. During videonystagmography, the roll testing to the right elicited a persistent geotropic nystagmus greater than that of left roll as was noted in his first visit to the clinic. The patient tolerated 5 CRM maneuvers well and was given instructions to avoid bending and lying down for the remainder of the day. The nystagmus did not resolve during the clinic visit.
At the follow-up visit 1 week later, the patient rated his vertigo as ranging from 0 to 2 out of 10. Both the Dix-Hallpike and roll tests were negative for nystagmus or symptom provocation.
This patient case illustrates an atypical presentation of acute onset disabling positional vertigo with blurred vision and a persistent direction changing geotropic nystagmus with an intensity that differed depending on whether the head was placed into the DHT or roll test positions. The most likely explanation for the difference in nystagmus between test positions is that the DHT did not create the same amount of cupular deflection (from either displaced otoconia or LC) as did the roll test. When the patient was placed in right roll, the kinocilia and stereocilia were positioned such that a greater excitation occurred compared with when the head was positioned in a right DHT. This illustrates that the roll test and DHT may not always agree, and the importance of using multiple head positions in supine to distinguish the intensity of a persistent geotropic nystagmus.
Spontaneous nystagmus and vertigo because of noncentral vestibular causes (ie, hSCC BPPV) are possible and have been reported in the literature.21 To assist with distinguishing the affected side in hSCC BPPV, it has been recommended that examining the direction of nystagmus with the head placed in pitch (ie, “bow and lean test”) can be useful.12 We did not include the bow and lean test, although it has been shown to assist in identifying the affected ear in 35.7% of patients with confirmed hSCC BPPV.10 Our patient demonstrated a high-velocity (>30°/s), nonfatiguing and persistent geotropic nystagmus. Although one prior study reported the duration of canalithiasis in the hSCC lasting as long as 91 seconds, ultimately the nystagmus did slow down and stop in every case.1 The duration of the nystagmus we report may have been longer because of an abnormal velocity storage system, a circuit of neurons within the brainstem and cerebellum that perseverate the nystagmus beyond the time typically caused by cupular deflection (∼6 seconds).22 Velocity storage is abnormally long in patients who have lost cerebellar inhibition.23,24 We do not believe this explains the responses in our patient, given we found no evidence for central pathology on the basis of his oculomotor examination (including normal head impulse, smooth pursuit, and saccadic testing) or history, and he had a separate, recurrent episode. An equally doubtful diagnosis for the persistent positional-induced geotropic nystagmus in our patient is that of vestibular migraine. This is unlikely based on our patient's age25,26 but also for 2 additional reasons: (1) our patient did not meet the criteria for vestibular migraine18 and (2) the mean peak slow-phase velocity reported in those with definite migraine is much slower (∼12-20°/s) compared with our 62 to 74°/s peak slow-phase velocity.7
We believe the most likely explanation for our case is that it represents a manifestation of LC. Unfortunately, both hSCC BPPV and LC share several characteristics (Table). In our case however, the expected pattern of rules for both hSCC BPPV and LC was violated. The treating clinician missed 2 findings in the examination of this patient's persistent direction-changing geotropic nystagmus: (1) When placed in supine, the patient developed a right-beating nystagmus, suggesting either an LC deflected in the inhibitory direction in the left ear or BPPV of the left ear. The geotropic direction of the nystagmus during the supine roll test ruled out the cupulolithiasis variant of BPPV. (2). During the CRM treatment for a presumed right hSCC canalithiasis, the patient was positioned in prone position (after previously lying on his left side) and developed a persistent right-beating nystagmus. The fact that the nystagmus persisted ruled out the canalithiasis variant of BPPV. What makes this case unique is the fact that the direction of the horizontal nystagmus was not of opposing directions when tested in the prone and supine positions.11,21
We recognize 2 limitations of our evaluation in this case, including (1) not performing a thorough clinical examination at the initial visit with oculomotor tests (ie, cover/uncover test) that would help distinguish central vestibular causes of pathology from peripheral ones, and (2) not performing the null point examination or the bow and lean test to assist diagnosing the cause for the persistent geotropic nystagmus.
To help distinguish causes of persistent geotropic nystagmus, we suggest 4 clinical components prudent for clinicians to include: (1) wait a sufficient length of time for the nystagmus to stop (∼2 minutes), (2) test for fatigue by repeating the positional nystagmus tests, (3) incorporate a head flexion component as part of the positional testing, and (4) attempt to identify a null point by rotating the head toward either side slowly, perhaps as much as 40°.
Our case study illustrates a complex presentation of persistent direction-changing geotropic nystagmus with vertigo that was not clearly related to LC or hSCC canalithiasis. In the examination of persistent geotropic nystagmus, our case suggests head position can create differing intensities of nystagmus (roll test vs Dix-Hallpike) and that it is critical for clinicians to carefully examine the nystagmus for duration, effects of repeat testing, the effect of head flexion, and the presence of a null point to distinguish hSCC BPPV from LC.
The authors are grateful to Dale Roberts, MS, for help with graphics and James Chia-Cheng Lin, PT, PhD, and Brooke Klatt, PT, DPT, NCS, for assistance with video editing.
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