Discussion:
In sum, despite diagnosing the wrong side, the wrong canal, and applying the wrong treatment maneuver, the emergency department clinicians cured the patient’s BPPV.
Among patients experiencing acute vertigo symptoms, hcBPPV is often underdiagnosed in favor of pcBBPV.[2, 3] While the Dix-Hallpike Test (DHT) is the preferred test to diagnose pcBPPV, other diagnostic tests, such as the supine roll test (SRT), are often needed so that a diagnosis of hcBPPV is not missed.[4-7] Our simulations emphasize the importance of performing these diagnostic tests using standardized maneuvers in a specific sequence. We have shown that the Dix-Hallpike maneuver can cause debris to move within the horizontal SCC, producing symptoms and potentially leading to a misdiagnosis of pcBPPV instead of hcBPPV. However, if the SRT is performed first, there will be little to no movement of particles within the posterior SCC, and even if there was movement in the posterior SCC, it would produce a vertical / torsional nystagmus pointing to the posterior SCC being the affected canal. This is consistent with the findings of Bhandari et al. (2022) and Li and Yang (2023), who showed that the sequence of performing the SRT steps can alter the position of otoconial debris within the canal as well as the resultant nystagmus patterns, which could lead to ambiguity of the type and side of a hcBPPV.[16, 17] Thus, following a protocol in which the SRT is performed first in patients with the triggered (positional) episodic vestibular syndrome should provide an optimal window to observe Ewald’s 1st law in action (“the plane of nystagmus parallels the anatomic plane of the semicircular canal that generated it”), with pcBPPV producing vertical / torsional nystagmus and hcBPPV producing horizontal nystagmus.[18]
These issues raise the question of whether the approach to BPPV should change to clinicians first performing the SRT to optimally assess for hcBPPV. If the SRT is negative, clinicians should then perform the DHT to optimally assess for pcBPPV. Alternatively, clinicians could be trained to start with the DHT but, more specifically, observe nystagmus patterns of pcBPPV or hcBPPV since the DHT triggers nearly all pcBPPV and at least half of hcBPPV.[19] Lastly, this case also raises the possibility that the approach to BPPV could be simplified for frontline doctors since it is possible that single maneuvers can treat multiple variants. Future clinical trials about training physicians in the approach to BPPV could better address this issue.
In our patient, in view of the inaccurate classification of BPPV in the emergency department, the “curative” effect of the Epley treatment was initially surprising. The Epley maneuver, if correctly performed, should be specific for resolving pcBPPV.[6] There have been anecdotal reports, however, that hcBPPV may resolve with the Epley maneuver, but it is unclear how the Epley maneuver was applied in those cases. Our simulation of a left Epley maneuver with extended (i.e., head turned too far) angulation of the head successfully resolving a right hcBPPV is like a proposed treatment maneuver for hcBPPV that involves starting in the supine position, turning the head towards the healthy side (left in our patient’s case) for 45°, then another 45° towards the healthy side, and then sitting up.[20] The optimal repositioning maneuvers for hcBPPV and pcBPPV are well-documented in prior studies and should be encouraged in clinical practice.
Our patient illustrates that a successful outcome does not always depend on the correct classification of BPPV and correct treatment. While the adage, “It’s better to be lucky than good,” may have been at play in this case, benefitting this patient, our results should not be interpreted to suggest that clinicians need not strictly follow testing or treatment protocols. Rather, our results suggest the opposite– that placing the head in the correct position for a canal-plane-specific BPPV is critical to interpreting nystagmus and accurate clinical diagnosis.
Limitations of our study include the lack of precise knowledge of how the testing and treatment maneuvers were performed by the clinical staff in the emergency department, the lack of precise knowledge of the nystagmus patterns observed by the treating clinician, the unavailability of the patient for evaluation by our research team after treatment, and the lack of follow-up data on the long-term response of the patient. It remains possible that the patient initially had pcBPPV, and the treating clinician’s repositioning moved the particles out of the posterior canal and into the horizontal canal – known as ‘canal switch.’ Furthermore, since there was only a small difference in the intensity of the horizontal nystagmus elicited in the two ear-down positions during the SRT, the localization of the offending labyrinth by the research team was primarily based on the response to the bow test. The lack of significant asymmetry between the two sides during the SRT could be related to the relatively low peak slow phase velocity of nystagmus induced in the SRT due to the relatively low velocity of the movements of the head to the ear down position.[21, 22] In this case, the head movements were not fast enough for Ewald’s 2nd law – excitation produces a stronger response than inhibition – to take effect. The asymmetry between right and left ear-down positions may be better brought out by moving the head quickly to the ear-down positions. Additionally, our simulations assume an average anatomical orientation of the canals, the membranous labyrinth, and the cupula.[15] The variability of the orientation of the canals in the head, the membranous labyrinth within them, and the cupula among individual subjects; the presumed differences among subjects in the location and constitution (otoconia and sluffed otolith membrane) of the debris within the SCCs; and the speed at which the head is brought to a new position in the diagnostic and treatment maneuvers, can all contribute to the uncertainty of the classification of the canal subtype of BPPV and of the effects of different treatment maneuvers.[1, 21-24] Despite these limitations, our analysis and simulations are most compatible with diagnosing a right-sided hcBPPV, treated with an extended left Epley maneuver for a misdiagnosed left-sided pcBPPV.