Vestibular function assessment using the video head impulse test and videonystagmoscopy in congenital nystagmus and vertigo: a long-term case report

Introduction

The vestibular function was primarily studied using the lateral vestibulo-ocular reflex (VOR), with low-frequency caloric and rotational tests recorded by electronystagmography (ENG; Baloh and Honrubia, 2001). In patients with congenital nystagmus (CN), these assessments were mainly confined to laboratory settings (Yee et al., 1981; Demer and Zee, 1984; Carl et al., 1985), using the search coil and ENG in clinical contexts; now, videonystagmography (VNG) is primarily used in both environments (Hathiram and Khattar, 2012; Khanna and Dell'Osso, 2006). CN, usually horizontal (Yee et al., 1976; Dell'Osso and Daroff, 1975), complicates these evaluations because it can interfere with coplanar VOR responses and even hinder their development (Demer and Zee, 1984; Carl et al., 1985). Research findings are inconsistent: some studies report absent or reduced VOR gain during caloric (Forssman, 1964; Yamazaki, 1979), rotational (Demer and Zee, 1984), and head-shaking oscillations (Carl et al., 1985) in darkness, while others show normal mean gain at low-frequency stimulation (Yee et al., 1981). Normal gains during foveation periods with active head movements at 1 Hz have also been observed, although assessing higher frequencies remains challenging (Dell'Osso et al., 1992). Such discrepancies, driven by patient variability, testing methods, CN waveforms, and VOR impact underscore the difficulty of reliably evaluating vestibular function, especially at high frequencies and in clinical practice.

The introduction of vestibular evoked myogenic potentials enabled assessment of the otolithic organs in patients with CN (Manzari et al., 2012). The search coil technique, and later the video head impulse test (vHIT), expanded evaluation to each SCC at high frequencies (Weber et al., 2009; Curthoys and Manzari, 2017). We recently reported the first vHIT-based assessment of a patient with CN and vertigo (Denia-Lafuente and Lombardero, 2021). Persistent lateral VOR abnormalities were observed before and after recovery from vestibular neuritis (VN), but without symptoms, suggesting that central adaptive mechanisms related to CN, rather than a bilateral vestibular injury, were responsible (Denia-Lafuente and Lombardero, 2021). Further evidence is needed to confirm these observations, which, to our knowledge, have not been previously reported (Denia-Lafuente, 2025c).

Videonystagmoscopy (VNS), which allows recording and playback, enables the precise examination of eye movements essential for the diagnosis and treatment of vestibular disorders (Vitte et al., 1995). Here, we describe the peripheral vestibular function of a new patient with CN, migraine, and vertigo, assessed with both vHIT and VNS.

Case presentation

Case description

A 56-year-old female professional with a history of CN, migraine, and episodic vertigo presented to the emergency department after 3 days of severe headache followed by vertigo, persistent imbalance, nausea, and bilateral tinnitus, more pronounced in the left ear, without hearing loss. A neurological workup, including brain computed tomography (CT), revealed spontaneous left-beating nystagmus and findings consistent with episodic migraine. She received vestibular sedatives and rizatriptan benzoate and was referred for further evaluation. Previous neurological examinations, including brain magnetic resonance imaging, had shown no other relevant findings.

She reported episodes of vertigo lasting 2–3 days for approximately 27 years, sometimes while in bed, and tinnitus in the left ear for the last 3 years. Since she reached menopause, these episodes had been associated with migraines, sometimes preceding them, with photophobia and phonophobia, and occasionally antedated by bilateral ear pressure and tinnitus specially in the left ear. She described fluctuating, non-permanent hearing loss, frequent spatial disorientation in open spaces, and a history of childhood strabismus. No family history of migraine was reported. She used progressive occupational glasses but not for distance. Her Dizziness Handicap Inventory (DHI) was 60.

Diagnostic tests and follow-up

Clinical and VNG examination using the Interacoustics VN415 system (Interacoustics S.A., Middelfart, Denmark) revealed a high-frequency, horizontal, jerk, left-beating nystagmus in primary gaze, which intensified in left gaze (3,3 b/s, aSFV: 24.6°/s) and changed direction, decreasing in right gaze (Figure 1A). CN limited vestibular assessment, including observation of spontaneous nystagmus, head shaking, vibration-induced nystagmus, and head impulse tests (HITs), as well as during VNG. Despite this, the right (R) Dix-Hallpike (DHR) test with VNS (Interacoustics Micromedical VisualEyes 505) elicited, after 2–3 s, intense mixed, upbeat, and right-torsional nystagmus lasting about 18 s with severe vertigo (Supplementary Video S1). The balance tests were normal.

The patient was diagnosed with CN, VM and right posterior canalolithiasis benign paroxysmal positional vertigo (BPPV) (Lempert et al., 2022). Positional testing performed after an Epley maneuver confirmed the absence of positional nystagmus and vertigo in the DHR position, although mild vertigo and imbalance with an upward CN component were noted when sitting. A second maneuver revealed no nystagmus or vertigo.

At the 15-day follow-up, the presenting symptoms, vertigo and unsteadiness, had resolved. Positional testing using VNS was normal. vHIT was systematically performed with both spontaneous nystagmus suppression disabled (SN off) and enabled (SN on; ICS Otometrics, 2015). With SN off, a low lateral HIMP and SHIMP acceptance rate and frequent rejections were observed; therefore, results are reported with SN on, showing a normal acceptance/rejection rate (Supplementary Figures S1, S2). Lateral HIMP revealed reduced gain values and impaired bilateral horizontal VOR generation. During passive head impulses (HIs), compensatory saccades with a spectrum of latencies were identified, including very early (near-zero latency or with the onset of head acceleration), early covert (during head acceleration), and covert saccades occurring during the deceleration phase of the HI (≈100–140 ms; Sjögren et al., 2018; Weber et al., 2008; Sjögren et al., 2021). These were predominantly rightward impulses, frequently exhibiting a double-peaked saccadic response (Figure 1B, Supplementary Figure S3). A complete saccade analysis and eye movements are shown in Supplementary Figure S1 and Supplementary Video S2. Direction-changing CN appeared mainly as anticompensatory eye movements to the left and compensatory movements to the right. Vertical canal VOR gains remained normal for each SCC, without refixation saccades (Figure 1B).

Pure-tone audiometry (PTA), vestibular evoked myogenic potentials (cVEMP and oVEMP), and the Clinical Test of Sensory Interaction and Balance (CTSIB) results (Horn et al., 2015) showed no abnormalities.

The findings from across visits 1–9 appear in Figure 2. A severe COVID-19 infection prevented her visit at 6 months. The patient returned at 2 years 9 months, after the lockdowns and a prolonged period free of the initial presenting symptoms. At each visit, we documented her symptoms and findings from physical examinations, DHI scores at the first and the final six visits, and Visual Function Questionnaire (VFQ-25; Mangione et al., 2001), Spanish survey (Visual Function Questionnaire (VFQ-25), 2001), scores on visits 5 and 8. Positional testing was performed on visits 1–4 and 6. The HIMP test was performed during the second visit and together with SHIMP on visits 3, 4, and 7–9, providing repeated VOR stimulation throughout follow-up. Vertical canal VOR function, cVEMPs, oVEMPs, and the CTSIB were completed during visits 2 and 4. PTA was performed during visit 2; VNG during visits 2, 5, and 9. At 3 years 3 months, a binocular vision assessment was performed, and new optical corrections were prescribed. Time-series data for vHIT with SN on, together with the impulse rejection/acceptance rate, appear in Supplementary Figures S1, S4–S8 and with SN off in Supplementary Figure S2.

Results at 3 months and at 2 years 9 months are jointly reported for comparison, including symptoms, physical examination, tests, diagnosis, and treatment (Figure 2). At 3 months, positional tests were normal, and at 2 years 9 months they revealed left posterior canalolithiasis, which was resolved with an Epley maneuver, after a mild (m) COVID-19 infection. VEMPs and the CTSIB showed no abnormalities (DHI 38).

For comparison, lateral HIMP at 3 months and at 2 years 9 months are shown alongside those at 15 days, revealing similar mean lateral VOR gains (Figure 3). At 3 months, bilateral early HI covert saccadic responses tended to group toward the deceleration phase of the impulse, with overt saccades grouping to the right (Figure 3, Supplementary Figure S4). At 2 years 9 months, covert saccades showed progressive grouping (Figure 3, Supplementary Figure S5). SHIMP VOR gains were comparable on both sides at two visits but remained below HIMP values (Figure 4). Saccade analysis showed low bilateral anticompensatory amplitudes, greater to the left, and 5% rightward covert compensatory saccades at 3 months, which were absent at 2 years 9 months (Figures 4, Supplementary Figures S4, S5).

At 3 years 3 months, a binocular visual function test was requested due to persistent, non-vertiginous symptoms limiting daily activities (DHI 38). It revealed several anomalies, leading to new optical corrections with separate lenses for near and distance vision (Khanna and Dell'Osso, 2006; Zahidi et al., 2017; Figure 2). The patient scored 86% on the VFQ-25 when wearing her occupational lenses.

At 4 years 3 months, after an mCOVID-19 infection, the patient complained of vertigo, among other symptoms (DHI 40). A DHR test revealed posterior canalolithiasis, resolved with an Epley maneuver. She had only been using her glasses for near vision (previous bad experience with her distance lenses), feeling better at work but worse and dizzy with her distance vision. She was advised again to use both pairs of lenses (Figure 2).

At 4 years 6 months, her symptoms had improved (DHI 30; Figure 2). Lateral HIMP testing revealed VOR gains comparable to previous ones, slightly reduced on the right, with tighter covert saccade grouping (Figure 3, Supplementary Figure S6). SHIMP trials also showed similar values to previous tests, although with somewhat lower gains (Figure 4, Supplementary Figure S6). She had been using both pairs of glasses for 1.5 months.

At 4 years 8 months the patient reported being satisfied using both pairs of glasses, (DHI 28, VFQ-25 91%; Figure 2). Lateral HIMP showed the lowest VOR gains, with highly organized covert saccades (Figure 3, Supplementary Figure S7). SHIMP gains and saccade patterns were mostly stable (Figure 4, Supplementary Figure S7).

At 5 years, the patient reported better global steadiness, no vertigo, greater visual stability, and fewer headaches. She wore the new glasses daily. CN exhibited the maximum intensity on the left gaze (3,6 b/s; aSFV: 30.3°/s; Figure 2). Lateral HIMP showed somewhat higher VOR gains, with persistent organization of covert saccades (Figure 3, Supplementary Figure S8). SHIMP VOR gains were the highest recorded during follow-up, and the saccades' amplitude and PR were somewhat higher than in the previous test (DHI 20; Figure 4, Supplementary Figure S8).

From the patient's perspective (Riley et al., 2017), at 3 months, she reported resolution of the initial presenting symptoms. At 2 years 9 months, she reported that before coming to our office, she missed work at least twice a month on days when she had disabling vertigo and that, after treatment, she has not missed work again. At 4 years 8 months and at 5 years, progressive improvement persisted, with a marked reduction in vertigo and greater visual stability, which contributed to improved balance and well-being (Figure 2).

Adherence (Riley et al., 2017) to the initial recommendations was maintained until loss to follow-up during the COVID-19 pandemic, a prolonged symptom-free period, and limited availability. Adherence resumed upon return to treatment, although the delayed implementation of the recommendations prolonged the treatment course, allowing the completion of the management plan (Figure 2).

Discussion

We show that the CN waveform may condition vHIT-recorded lateral VOR eye movements. This jerk CN with extended foveation favored visual acuity (Dell'Osso and Daroff, 1975), enabling standard calibration without the prolongation observed in our prior case (Denia-Lafuente and Lombardero, 2021) while increasing rejection rates during HIMP/SHIMP with SN off; this effect resolved with SN on, without affecting gain.

These results confirm our earlier findings regarding the utility of vHIT in evaluating the function of each SCC in patients with CN and vertigo (Denia-Lafuente and Lombardero, 2021). In this case, selective horizontal SCC abnormalities interfered with the VOR, including reduced gain and compensatory saccadic eye movements but with distinct features. Specifically, at first, we observed early and very early covert saccades during passive HI, very similar to those during active HI that other authors have described (Sjögren et al., 2021; Black et al., 2005), which we use in our VOR training sessions in vestibular rehabilitation (Denia-Lafuente and Lombardero, 2021). These early responses appeared to represent a different anticipatory adaptation/substitution VOR mechanism from the more common covert and overt saccades that occur, respectively, during and after the deceleration phase of HI in vestibular disorders (Sjögren et al., 2018; Batuecas-Caletrio et al., 2014). To our knowledge, very early saccades during passive HIs have not been specifically characterized in the literature (Denia-Lafuente, 2025b). Only a few studies have reported early saccades in vestibular lesions (Weber et al., 2008) under these conditions, as observed in the present case.

The initial gains of lateral HIMP, lower than normal but higher than in our previous case (Denia-Lafuente and Lombardero, 2021), could be related to the effect of early covert saccades, along with vestibular function, even if deficient (Sjögren et al., 2018; Black et al., 2005). The effect of saccades on gain can be clearly appreciated during the SHIMP protocol, which removes them, showing lower accurate values. In addition, the presence of SHIMP anticompensatory saccades in a difficult-to-assess lateral VOR can be a very useful sign of vestibular function (MacDougall et al., 2016). In turn, anticompensatory saccades generation through training can promote vestibular compensation and/or functional recovery (Shen et al., 2016).

The passive HIMP protocol demonstrated new progressive and persistent changes at follow-up (Denia-Lafuente, 2025b), with a shift from a dispersed saccadic response to a clustered pattern of covert saccades, compatible with compensated vestibular deficits (Batuecas-Caletrio et al., 2014; Curthoys and Halmagyi, 2014), with consistently low gains. We believe that repeated use of passive HIMP trained this patient to detect and reduce retinal slip errors by gradually increasing the number of saccades, adjusting their latency during the deceleration phase, as shown in their analysis, and improving gaze stability and functional recovery (Batuecas-Caletrio et al., 2017). Our findings suggest the contribution of passive HIMP adaptation/substitution mechanisms in severe eye–head misalignment through jerk CN and lateral VOR interaction.

CN does not interfere with vertical VOR function, allowing normal and abnormal vestibular response patterns to be observed, as shown in this case and the previous one (Denia-Lafuente and Lombardero, 2021). Therefore, we emphasize again the importance of its routine study. To our knowledge, this is the first reported case using VNS for the accurate diagnosis and successful treatment of posterior SCC BPPV in a patient with CN and vertigo (Denia-Lafuente, 2025a).

The vHIT findings could mimic those of a vestibular lesion specific to both lateral SCCs, but the patient's history and examinations did not indicate any such peripheral (Strupp et al., 2017; Mancino-Moreira et al., 2021) or central (Chen and Halmagyi, 2018; Lee et al., 2018) bilateral disorder other than BPPV and VM, in addition to CN. Although BPPV can coexist with other vestibular disorders, including bilateral vestibulopathy (BVP), which is more frequent in migraines, our vHIT results were unlike those seen in such cases (Baloh et al., 1987; Pérez-Fernández et al., 2023; Kim et al., 2019). Transient lateral SCC hypofunction from otoconia entrapment also fails to explain our findings (Castellucci et al., 2019; Strupp et al., 1995). Migraine has been linked to BVP, sometimes with a familial pattern, raising the possibility that recurrent vertigo in VM could be associated with a sequential clinical subtype of BVP (Strupp et al., 2017; Lucieer et al., 2016), although no genetic linkage has been demonstrated to date (Frejo et al., 2016; Mei et al., 2021). Saccades, especially in the lateral SCCs, are the most common vHIT finding during or shortly after VM episodes and may persist depending on treatment, often without gain reduction (Du et al., 2023; Koç and Akkiliç, 2022; Choi et al., 2022). In contrast, severe and persistent bilateral vestibular abnormalities between episodes in our case are atypical for VM (Lempert et al., 2022). Taken together, the absence of comparable lateral VOR findings in BPPV or VM strongly suggests that CN is the most likely cause in this patient.

DHI scores were broadly consistent with the patient's reported experience of treatment (Riley et al., 2017) up to 2 years 9 months, despite periods of interrupted adherence. Further improvement took time and was likely driven by lateral VOR compensation/substitution mechanisms and optical corrections. The VFQ-25 did not capture the degree of disability or improvement, suggesting the need for a nystagmus-specific questionnaire (McLean et al., 2016; Das et al., 2018).

There were no technical limitations in performing the vHIT. Restrictions associated with a single-case report are evident. The main challenges were related to the abnormal lateral VORs and the disorganized passive HI saccadic response, which complicated the interpretation of the initial results, their progression, and the clinical implications. Very early and early covert compensatory saccades have been linked to preprogrammed eye movements (PPEMs) associated with active HI (Sjögren et al., 2021; Herdman et al., 2001) and, less frequently, early saccades with passive stimuli (Weber et al., 2008; Tian et al., 2000). A cyclic ocular motor pattern in CN may contribute to early passive saccadic responses, potentially reflecting preprogrammed gaze stabilization mechanisms (Haggerty and King, 2018), consistent with vestibular–saccadic interactions observed in vestibular hypofunction (Colagiorgio et al., 2017). The remaining lateral VOR likely played an important role during passive HI in the progressive coupling of saccades, similar to patterns described in compensated vestibular lesions (Curthoys and Halmagyi, 2014). Evidence supports that PPEMs and the VOR work together to stabilize gaze (Haggerty and King, 2018), and our findings suggest that CN does so as well. Considering the patient's functional recovery over time, its rehabilitative effectiveness suggests a potential clinical applicability in comparable cases. Although prolonged follow-up might be expected to reduce adherence, it allowed us to observe a gradual improvement in lateral VOR adaptation. The effects persisted after each passive HIMP regardless of the time interval between visits. While the absence of direct measurements, such as DVA and/or functional HI tests (Corallo et al., 2018), is a limitation, this is partly mitigated by strong evidence showing that covert saccades correlate with improvement in both domains and the DHI score (Matiñó-Soler et al., 2016). Key questions remain, underscoring the need for further research into the mechanisms underlying CN and its interaction with visuo-vestibular adaptation.

In summary, this report reinforces the clinical utility of vHIT in CN and vertigo. It identifies lateral VOR impairment, characterized by reduced gain and a markedly disorganized pattern of early saccadic responses during passive HIMP testing, a finding that appears to be linked only to CN. An accurate assessment of lateral VOR function required SHIMP testing, which provided clearer measurements when HIMP responses were difficult to interpret. This case also offers new insights into the diagnosis and management of vertical SCC BPPV without interference from CN. Our results provide evidence on new passive lateral HIMP visuo-vestibular compensatory mechanisms, including training, learning, and retention, for which CN waveform and remaining vestibular function appear essential. An updated binocular vision study is recommended in these patients.

In conclusion, our findings provide further evidence that vestibular function assessment in CN and vertigo using vHIT and VNS enables accurate diagnosis and successful management of the most common vertigo syndromes, VN, and posterior SCC BPPV, whether or not associated with VM.

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Supplementary material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fauot.2026.1917636/full#supplementary-material

vHIT recording at 15 days. HIMP, SN on. Highly disorganized lateral vestibulo-ocular reflex (VOR) with low gain and markedly scattered saccadic-like eye movements throughout the head impulse (HI), mainly to the right. Normal HI acceptance rate. Normal vertical VOR. Supplementary material at the source

vHIT recording at 15 days. HIMP, SN off. Disorganized lateral vestibulo-ocular reflex (VOR) with low gain and scattered saccadic-like eye movements throughout the head impulse (HI). Very low lateral HI acceptance rate with frequent rejections. Normal vertical VOR. Supplementary material at the source

Isolated lateral HIMP traces showing head and eye velocity over time, derived from the recordings presented in Supplementary Figure S1 using MATLAB. Detail of very early saccades (near-cero latency or occurring at the onset of head acceleration), early covert saccades (during head acceleration), covert saccades (during the deceleration phase), and overt saccades (after the head impulse). Head velocity: rightward, red; leftward, blue. Eye velocity: green. Supplementary material at the source

vHIT recording at 3 months. Lateral HIMP and SHIMP. Early bilateral head impulse saccadic responses and rightward overt saccades tend to cluster toward the deceleration phase. Stable HIMP gains. Lower SHIMP gains. Bilateral anticompensatory saccades with a smaller amplitude to the right. Supplementary material at the source

vHIT recording at 2 years 9 months. HIMP and SHIMP. A sustained increase in saccade grouping is observed in HIMP. SHIMP gains were comparable with previous ones, remaining below HIMP values. Normal vertical vestibule-ocular reflex. Supplementary material at the source

vHIT recording at 4 years 6 months. Lateral HIMP and SHIMP. Lateral HIMP ongoing organization of covert saccades converging during the head impulse deceleration phase, with gain fluctuations. SHIMP trials show similar values to previous tests with somewhat lower gains. Supplementary material at the source

vHIT recording at 4 years 8 months. Lateral HIMP and SHIMP. Increase in well-organized lateral HIMP saccades with stable low gains. SHIMP gains and saccade patterns show minimal variations. Supplementary material at the source

vHIT recording at 5 years. Lateral HIMP and SHIMP. Lateral vestibulo-ocular reflex patterns become more consistent. HIMP gains increased, with the highest values observed in SHIMP. Supplementary material at the source

Dix-Hallpike (DH) right test using infrared videonystagmoscopy on 1st visit. Real-time recording. At the beginning of the video, we observe the patient's congenital nystagmus (CN) up to about 2–3 seconds after acquiring the DH position, followed by an intense mixed upbeat and right-torsional paroxysmal positional nystagmus lasting around 18 seconds. Subsequently, the CN reappears. Supplementary material at the source

vHIT lateral HIMP using infrared videonystagmoscopy at 15 days. Passive horizontal head impulses (HI) in our patient with congenital nystagmus (CN). Compensatory eye movements, corrective saccades, and CN are observed in real time on both sides, more pronounced with HI to the right. Supplementary material at the source

Footnotes

Edited by: Leonardo Manzari, MSA ENT Academy Center, Italy

Reviewed by: Francesco Comacchio, University Hospital Sant'Antonio, Italy

Cristiano Balzanelli, Vertigo Center San Bernardino Poyclinic, Italy