The most common form of posterior canal benign paroxysmal positional vertigo (BPPV) is characterised by positional, paroxysmal, upbeat nystagmus, with a torsional component beating towards the downward ear. Rarer variants have been reported, putatively due to either the position of otoconia in the canal or anatomic variations of the semicircular canals. The most frequent less common form is apogeotropic posterior canal BPPV, in which the positional nystagmus is downbeat and torsional apogeotropic. In this form, the main problems are differential diagnosis with central mimics of BPPV and identification of the affected canal and its side. The authors propose a new subtype of apogeotropic posterior canal BPPV hypothesising the localization of otoconia in the ampullary tract of the affected canal, which might explain the modality of the conversion in typical posterior canal BPPV which they observed in some of these cases. If nystagmus of the less common forms of posterior canal BPPV is explicable through purely peripheral mechanisms, these forms should no longer be defined as “atypical” but, in a less demanding way, as “less common” variants, which must be recognised by any expert otoneurologist.

The Hyperventilation Test is widely used in the "bed-side examination" of vestibular patients. It can either activate a latent nystagmus in central or peripheral vestibular diseases or it can interact with a spontaneous nystagmus, by reducing it or increasing it. Aims of this study were to determine the incidence, patterns and temporal characteristics of Hyperventilation-induced nystagmus in patients suffering from vestibular diseases, as well as its contribution to the differential diagnosis between vestibular neuritis and neuroma of the 8th cranial nerve, and its behaviour in some central vestibular diseases. The present study includes 1202 patients featuring, at vestibular examination, at least one sign of vestibular system disorders or patients diagnosed with a "Migraine-related vertigo" or "Chronic subjective dizziness". The overall incidence of Hyperventilation-induced nystagmus was 21.9%. It was detected more frequently in retrocochlear vestibular diseases rather than in end-organ vestibular diseases: 5.3% in Paroxysmal Positional Vertigo, 37.1% in Menière's disease, 37.6% in compensated vestibular neuritis, 77.2% in acute vestibular neuritis and 91.7% in neuroma of the 8th cranial nerve. In acute vestibular neuritis, three HVIN patterns were observed: Paretic pattern: temporary enhancement of the spontaneous nystagmus; Excitatory pattern: temporary inhibition of the spontaneous nystagmus; Strong excitatory pattern: temporary inversion of the spontaneous nystagmus. Excitatory patterns proved to be time-dependent in that they disappeared and were replaced by the paretic pattern over a period of maximum 18 days since the beginning of the disorder. In acoustic neuroma, Hyperventilation-induced nystagmus was frequently observed (91.7%), either in the form of an excitatory pattern (fast phases towards the affected site) or in the form of a paretic pattern (fast phases towards the healthy side). The direction of the nystagmus is only partially related to tumour size, whereas other mechanisms, such as demyelination or a break in nerve fibres, might have an important role in triggering the situation. Hyperventilation-induced nystagmus has frequently been detected in cases of demyelinating diseases and in cerebellar diseases: in multiple sclerosis, hyperventilation inhibits a central type of spontaneous nystagmus or evokes nystagmus in 75% of patients; in cerebellar diseases, hyperventilation evokes or enhances a central spontaneous nystagmus in 72.7% of patients. In conclusion the Hyperventilation Test can provide patterns of oculomotor responses that indicate a diagnostic investigation through cerebral magnetic resonance imaging enhanced by gadolinium, upon suspicion of neuroma of the 8th cranial nerve or of a central disease. In our opinion, however, Hyperventilation-induced nystagmus always needs to be viewed within the more general context of a complete examination of the vestibular and acoustic system.

To determine the utility of the hyperventilation test (HVT) in the diagnosis of vestibular schwannoma (VS). A retrospective analysis of hyperventilation-induced nystagmus (HVIN) in 45 patients with unilateral VS. A tertiary referral center. Forty-five patients with VS; 30 patients with chronic vestibular neuritis; 20 healthy subjects with normal hearing and without symptoms or a history of vertigo, migraine, or neurological diseases (control group). Audiological and vestibular examination; "side-stream" measurement of end-tidal CO2 pressure (P(EtCO2)) to standardize the procedure; magnetic resonance imaging (MRI) centered on the cerebellopontine angle. An analysis of HVIN, its patterns, and its appearance threshold via the measurement of P(EtCO2) correlations with the tumor size. HVIN was observed in 40 of 45 cases (88.9%) in the schwannoma group and in 12 of 30 cases (40%) in the chronic vestibular neuritis group; HVIN was not observed in the control group (0/20 cases) (p < 0.001). In the schwannoma group, HVIN was evoked at a mean P(EtCO2) value of 16.5 ± 1.15 mm Hg. The hypofunctional labyrinth was identified with high sensibility and specificity through caloric test, head shaking test, and head thrust test. The excitatory pattern, which included HVIN with slow phases that beat toward the hypofunctional side, and the paretic pattern, which included HVIN with slow phases that beat toward the hypofunctional side, were not significantly associated with VS size (19.04 ± 10.56 mm for the excitatory pattern and 19.06 ± 11.01 mm for the paretic pattern). The difference in the VS size in HVIN+ (19.05 ± 10.60 mm) and HVIN- (8.40 ± 2.19 mm) cases was significant (p = 0.009). A 60-second hyperventilation event causes metabolic changes in the vestibular system and reveals a latent vestibular asymmetry. The presence of an excitatory pattern is the major criterion that suggests VS in patients with signs of unilateral vestibular deficit.

The aim of the review is to value the incidence, patterns and temporal characteristics of hyperventilation-induced nystagmus (HVIN) in patients suffering from vestibular diseases, as well as its contribution to the differential diagnosis between vestibular neuritis and schwannoma of the eighth cranial nerve and its behavior in some central vestibular diseases. The hyperventilation test seems to be more useful than other bedside tests in detecting schwannoma of the eighth cranial nerve in the case of sudden monolateral hypacusia. The presence of an excitatory pattern of HVIN in vestibular schwannoma that has undergone to stereotactic surgery reveals that this therapy produces demyelinization in neural fibers. The hyperventilation test is easy to perform, well tolerated and able to reveal latent vestibular asymmetries; it acts both at peripheral and central vestibular levels through metabolic mechanisms or, more rarely, through changes in cerebrospinal fluid pressure. It can provide patterns of oculomotor responses suggesting the execution of gadolinium-enhanced MRI, upon the suspicion of schwannoma of the eighth cranial nerve or of a central disease. In our opinion, the presence of HVIN always needs to be viewed within the more general context of a complete examination of auditory and vestibular systems.

Gli obiettivi dello studio sono stati: identificare segni di sofferenza vestibolare attraverso un protocollo di “bed-side examination” in caso di ipoacusia improvvisa monolaterale senza segni clinici di sofferenza vestibolare; proporre i risultati della bed side examination vestibolare come criterio per l’esecuzione mirata della RMN per i canali acustici interni in caso di sospetto di neurinoma dell’ VIII nervo cranico. Sono stati valutati 96 pazienti, 52 uomini e 44 donne, con ipoacusia improvvisa neurosensoriale monolaterale che non presentavano né vertigine né nistagmo spontaneo. Sono stati eseguiti: esame audiometrico tonale, esame impedenzometrico con test di Anderson per la ricerca di adattamento, Head Shaking Test, Test Vibratorio, Head Impulse Test, Test di iperventilazione, ricerca del nistagmo posizionale in posizione supina e nei decubiti laterali; l’ABR è stato eseguito nei pazienti con segni di sofferenza vestibolare se con soglia tonale ai toni acuti migliore di 70 dB nHL; tutti i pazienti con ipoacusia improvvisa hanno eseguito RMN con gadolinio per i canali acustici interni. Segni di sofferenza vestibolare sono stati identificati in 22/96 pazienti (22.9%) e la RMN ha evidenziato la presenza di schwannoma dell’ VIII nervo cranico in 5/96 casi (5.2%), tutti con segni di sofferenza vestibolare evidenziati alla “vestibular bed-side examination”. I nostri dati hanno evidenziato che gli schwannomi dell’ VIII nervo cranico sono stati individuati solo nei casi di ipoacusia improvvisa monolaterale con segni di deficit vestibolare omolaterale. L’indicazione alla RMN con gadolinio può quindi essere limitata solo a questi casi, con evidente beneficio organizzativo ed economico.