Visual Suppression is Impaired in Spinocerebellar Ataxia Type 6 but Preserved in Benign Paroxysmal Positional Vertigo

Effect of ocular fixation on positional nystagmus in BPPV patients

OBJECTIVE

The quantitative suppression rate of positional nystagmus (PN) by ocular fixation (OF) is unknown. This study aims to analyse the effect of OF on the slow phase velocity (SPV) of PN during diagnostic positional manoeuvres (DPMs) with videonystagmography in patients with benign paroxysmal positional vertigo (BPPV).

DESIGN

DPMs were performed on 58 patients with BPPV, 33 (56.9%) of whom were women. OF was initiated when PN was most evident, and recording was continued. The mean SPV of three consecutive nystagmus before (F0) and after (F1) OF initiation was calculated. The rate of suppression of PN by OF was found in percent with the formula (F0 - F1) x 100/F0.

STUDY SAMPLE

58 patients were included in this study.

RESULTS

The mean age was 56.1 ± 11.2 (range 27-76). F0 and F1 values were calculated as 5.742 ± 5.589 and 1.948 ± 3.424 degrees/second, respectively (p < 0.001). The rate of suppression of PN by OF was found to be 66.1%.

CONCLUSIONS

OF significantly suppresses PN during DPMs in BPPV patients. Elimination of OF during DPMs is important for accurate diagnosis.

Central mimics of benign paroxysmal positional vertigo: an illustrative case series

Benign paroxysmal positional vertigo (BPPV) is the most common peripheral vestibular disorder that is diagnosed based solely on clinical findings. Rarely, central lesions can present with positional vertigo and nystagmus, mimicking BPPV. Recognised red flags that may help distinguish central mimics from BPPV include the presence of additional neurological symptoms and signs, atypical nystagmus patterns, and the absence of a sustained response to repositioning manoeuvres. We present seven cases that illustrate how heuristic bias may affect the detection of these features in practice. Furthermore, our cases suggest that isolated downbeat positional nystagmus (simulating anterior canal BPPV) and apogeotropic horizontal nystagmus on the supine roll test (simulating horizontal canal BPPV) should be considered additional red flags.

Central Positional Nystagmus: A Systematic Literature Review

Objective

To provide a systematic review of the clinical and radiological features of lesion-induced central positional nystagmus (CPN) and identify salient characteristics that differentiate central from peripheral positional nystagmus (PN).

Methods

Systematic literature search according to the preferred reporting items for systematic reviews and meta-analysis.

Results

A total of 82 patients from 28 studies met the participants intervention, comparison, outcomes, and study designs criteria for inclusion. An atypical direction of nystagmus for the stimulated canal was reported in 97.5% patients during Dix–Hallpike (D–H) and 54.5% upon supine roll testing. Five types of CPNs were identified during positional testing: positional horizontal nystagmus (pHN) (36.8%), positional downbeating nystagmus (pDBN) (29.2%), positional torsional nystagmus (pTN) (2.1%), positional upbeating nystagmus (pUBN) (2.1%), and a combination of the four profiles (29.9%). CPN was paroxysmal (<60 s) in 85% patients on straight head hanging (SHH), 63.9% on D–H, and 37.5% on supine roll, and had a latency <3 s upon positioning in 94.7% patients in which it was reported. Concurrent vertigo was reportedly present in 63.4% patients and 48.8% demonstrated other neurological signs. Radiologically, in 74.4%, there was mention of cerebellar involvement, isolated brainstem involvement in 8.5%, and 14.6% involved the fourth ventricle.

Conclusion

Currently, there is a lack of robust data on the clinical and radiological characteristics of CPN highlighting the need for better phenotyping of CPN to help differentiate this entity from peripheral causes of PN. With increased awareness of CPN, particularly in the acute setting, we may see a change in the estimated prevalence of CPN and improved clinical markers to promptly identify the frequently sinister underlying causes.