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.