The Clinical Problem

A 52-year-old French woman presented with recurrent positional vertigo.

During the right Dix–Hallpike test, she developed downbeat nystagmus with a right torsional component. The pattern was initially interpreted as benign paroxysmal positional vertigo involving the right superior semicircular canal.

That diagnosis was anatomically plausible.

But plausible is not the same as secure.

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Clinical Reasoning: Step 1

Localize before naming the disorder

Positional vertigo may arise from:

• canalithiasis or cupulolithiasis;
• another peripheral vestibular disorder;
• neurovascular compression of the vestibular nerve;
• a central vestibular lesion; or
• posterior-circulation disease.

The direction and behavior of the nystagmus help localize the affected pathway.

Downbeat-torsional nystagmus during Dix–Hallpike testing can occur with superior-canal BPPV. Downbeat positional nystagmus, however, is also an important warning pattern for central or atypical vestibular disease.

Pause and consider

What additional features would strengthen the diagnosis of BPPV?

A reproducible canal-specific pattern, appropriate latency and duration, fatigability, and improvement after a correctly selected repositioning maneuver would all provide support.

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Clinical Reasoning: Step 2

Test the working diagnosis

The patient underwent multiple repositioning maneuvers.

Her symptoms and positional nystagmus persisted.

Treatment failure does not automatically disprove BPPV. A maneuver may be performed incorrectly, the wrong canal may be targeted, or uncommon canal variants may behave atypically.

Repeated failure nevertheless lowers confidence in the initial diagnosis—particularly when the presumed disorder is already uncommon.

Clinical pearl

A therapeutic maneuver can function as a diagnostic test only when its limitations are recognized. Failure should prompt reassessment, not endless repetition of the same assumption.

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Clinical Reasoning: Step 3

Reopen the differential diagnosis

The combination of persistent symptoms, downbeat-torsional nystagmus, and failure of repositioning raised several alternatives:

1. Persistent or atypical superior-canal BPPV
2. Central positional nystagmus
3. Vestibular migraine
4. Vertebrobasilar insufficiency
5. Structural posterior-fossa disease
6. Vestibular paroxysmia

At this stage, neurological examination, the precise temporal pattern of attacks, and appropriate neuroimaging become important.

The key question is whether the attacks still behave like displaced otoconia—or whether they suggest intermittent irritation of the vestibular nerve or a central pathway.

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Clinical Reasoning: Step 4

The MRI finding

Re-evaluation of magnetic resonance imaging demonstrated contact between the right anterior inferior cerebellar artery and the right vestibulocochlear nerve.

This neurovascular conflict supported vestibular paroxysmia.

The proposed mechanism is intermittent ephaptic excitation of the eighth cranial nerve at a site of vascular contact, producing brief recurrent vestibular symptoms.

But the image must be interpreted cautiously.

Clinical pearl

Neurovascular contact on MRI is supportive, not independently diagnostic. Similar contacts may be found in people without vestibular paroxysmia.

Imaging should therefore be reconciled with the clinical phenotype rather than allowed to replace it.

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The Diagnostic Pivot

The decisive change in reasoning came from discordance:

• the positional findings suggested superior-canal BPPV;
• repeated canalith-repositioning treatment did not produce the expected response; and
• MRI revealed a potential alternative mechanism involving the vestibular nerve.

The diagnosis was consequently reframed as probable vestibular paroxysmia mimicking superior-canal BPPV.

The word “probable” matters. It preserves the limits of the available evidence.

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What Was the Final Diagnosis?

Probable vestibular paroxysmia associated with right anterior inferior cerebellar artery contact with the vestibulocochlear nerve, presenting with a positional downbeat-right torsional nystagmus that mimicked right superior-canal BPPV.

This formulation does not claim that MRI contact alone proved causation. It integrates the atypical clinical course, treatment failure, observed nystagmus, and neurovascular finding.

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Differential Diagnosis at the Critical Decision Point

1. Superior-canal BPPV

The downbeat-torsional nystagmus and positional provocation supported this diagnosis. Its rarity and failure to respond to repeated appropriate maneuvers reduced its likelihood.

2. Central positional nystagmus

Downbeat nystagmus requires consideration of cerebellar, brainstem, craniocervical, degenerative, toxic, or vascular pathology. Appropriate neurological assessment and imaging are essential.

3. Vestibular migraine

Vestibular migraine can produce positional symptoms and variable nystagmus. Diagnosis requires the relevant migraine history and clinical criteria, which should not be inferred from positional symptoms alone.

4. Vertebrobasilar insufficiency

Vascular disease should be considered when symptoms are atypical, associated with focal neurological features, or linked to vascular risk. Positional provocation alone is insufficient.

5. Vestibular paroxysmia

Brief recurrent vestibular attacks, an atypical course, and compatible neurovascular compression support this possibility. MRI contact alone remains nonspecific.

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Why This Case Matters

BPPV is common, and recognizing it prevents unnecessary testing. That prevalence also creates a risk of premature closure.

The corrective strategy is not to image every patient with typical BPPV. It is to recognize the points at which the illness script no longer fits:

• an unusual canal assignment;
• atypical nystagmus;
• absent expected response;
• progression or persistence;
• neurological findings; or
• recurrent very brief attacks suggesting another mechanism.

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Clinical Pearls

1. Positional provocation describes a trigger; it does not establish the cause.
2. Downbeat positional nystagmus deserves heightened diagnostic attention.
3. Superior-canal BPPV is uncommon and should be diagnosed cautiously.
4. Repeated failure of an appropriate maneuver should reopen the differential.
5. Central positional vertigo must be considered when findings are atypical.
6. Neurovascular contact on MRI is supportive but not specific.
7. Localization should precede disease labeling.
8. Diagnostic language such as “probable” should be preserved when definitive criteria are not met.

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Potential Pitfalls

Pitfall 1: Equating a positive Dix–Hallpike test with posterior-canal BPPV

Better approach: Interpret the direction, latency, duration, fatigability, and reproducibility of the nystagmus.

Pitfall 2: Repeating repositioning maneuvers indefinitely

Better approach: Reassess the canal localization and alternative diagnoses after unexpected treatment failure.

Pitfall 3: Treating downbeat nystagmus as benign by default

Better approach: Consider central and other atypical vestibular causes.

Pitfall 4: Diagnosing vestibular paroxysmia from MRI alone

Better approach: Require clinical–radiological concordance and acknowledge that neurovascular contact can be incidental.

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Clinical Timeline

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Five Questions for the Reader

Question 1

Which finding most strongly prompted reconsideration of the initial BPPV diagnosis?

A. Positional symptom provocation
B. Right torsional nystagmus
C. Failure of repeated repositioning maneuvers
D. Female sex
E. Age over 50 years

Answer: C

Explanation: Persistent symptoms despite maneuvers appropriate for the presumed canal disorder created important diagnostic discordance.

Question 2

Which nystagmus feature should increase concern for an atypical or central cause?

A. Pure horizontal geotropic nystagmus
B. Persistent downbeat positional nystagmus
C. Brief upbeat-torsional nystagmus with fatigue
D. Physiological end-point nystagmus
E. Nystagmus suppressed after successful repositioning

Answer: B

Explanation: Downbeat positional nystagmus can occur in uncommon peripheral disorders but is also an important central warning pattern.

Question 3

What did MRI contribute in this case?

A. Definitive proof of vestibular paroxysmia
B. Exclusion of every central disorder
C. Evidence of right AICA contact with the vestibulocochlear nerve
D. Confirmation of superior-canal canalithiasis
E. Measurement of otoconia

Answer: C

Explanation: MRI identified a neurovascular conflict supporting the alternative diagnosis, but the finding was not independently diagnostic.

Question 4

Why is the diagnosis described as “probable”?

A. Positional vertigo cannot be diagnosed clinically
B. Neurovascular contact may be incidental, and the evidence did not establish causation with certainty
C. The patient had no nystagmus
D. BPPV and vestibular paroxysmia are identical
E. MRI cannot depict the vestibulocochlear nerve

Answer: B

Explanation: The diagnosis rests on clinical–radiological concordance while retaining uncertainty about the causal significance of the vascular contact.

Question 5

What is the best general lesson?

A. All positional vertigo requires MRI
B. BPPV should never be treated with repositioning maneuvers
C. A common diagnosis should be reconsidered when the observed course contradicts its expected behavior
D. Vascular contact always requires surgery
E. Downbeat nystagmus confirms vestibular paroxysmia

Answer: C

Explanation: Failure of the working model should prompt renewed localization and a broader differential rather than continued anchoring.

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Clinical Take-Home Message

Positional vertigo should not be equated automatically with BPPV.

When the nystagmus is downbeat or otherwise atypical, the presumed canal is unusual, or appropriately selected repositioning maneuvers repeatedly fail, clinicians should reconsider both peripheral and central alternatives.

Vestibular paroxysmia may mimic BPPV, but neurovascular contact on MRI is supportive rather than conclusive. The diagnosis should remain grounded in the complete clinical pattern.

Journal of Medical Case Reports is the world’s first international, PubMed-listed medical journal devoted to publishing case reports from all medical disciplines and will consider any original case report that expands the field of general medical knowledge, and original research relating to case reports. The journal is open access and strongly endorses the CARE guidelines for case reports, requiring authors to submit populated CARE checklists with submissions to improve transparency in reporting.