Nystagmus Does Not Belong to Vasovagal Syncope. If You Have Both, Something Is Unexplained.

A negative syncope workup is good news. It is not the same thing as a complete explanation.

The short answer

Vasovagal syncope is a reflex faint. It produces the familiar prodrome of nausea, warmth, sweating and greying vision, and it does not produce nystagmus, the involuntary rhythmic eye movement. So if someone faints and also has reproducible nystagmus in a particular head position, the vasovagal label explains the faint and leaves the eye movement unaccounted for.

That unaccounted-for finding is worth taking to a physician, because one of the conditions that produces exactly that combination is mechanical, positional, and invisible to a scan taken with the head held still.

What vasovagal syncope is, and what it is not

Answer first: vasovagal syncope is neurally mediated. A reflex drops heart rate and blood pressure, blood flow to the brain briefly falls, and the person faints. The prodrome is characteristic and the recovery is usually quick and complete.

What it does not do is produce the neurological findings of posterior circulation ischaemia. It does not cause nystagmus.

If the eyes are doing something in a particular head position, that is a mechanical or neurological finding. A reflex faint does not explain it.

The condition that produces the whole combination

Rotational vertebral artery occlusion, usually called Bow Hunter's syndrome, is reversible compression of a vertebral artery caused by rotating or extending the head. It is rare, and it is one of the few causes of vertebrobasilar insufficiency that is surgically treatable.

Its published symptom list is worth reading slowly: episodic dizziness or vertigo, potentially with nystagmus, tinnitus, syncope, blurred vision, nausea or vomiting. Symptoms typically resolve when the head returns to neutral.

That last part is the signature. Symptoms that arrive in a position and leave when the position does are behaving mechanically.

Nystagmus, tinnitus, syncope, blurred vision and nausea are one recognised constellation, not five unrelated complaints to be triaged separately.

Why a normal scan does not close the question

Answer first: the condition is defined by what happens when the head is turned, and standard imaging is taken with the head still.

Diagnosis is usually established with dynamic digital subtraction angiography, where the patient is asked to move the head into the provoking position during the study. Static imaging is generally ineffective at detecting position-related narrowing or occlusion. CT or MR angiography and transcranial Doppler can support the diagnosis but are not the same test.

So "the scan was clear" is a true statement that may have answered a different question than the one being asked.

None of this means an emergency workup was wrong or incomplete for its purpose. Ruling out the dangerous causes of syncope is exactly what an emergency department should do, and a negative result there is genuinely reassuring. It just does not, by itself, account for a positional finding.

The part a chiropractic journal has to say out loud

The published etiology list for Bow Hunter's syndrome includes atherosclerosis, thromboembolism, trauma, tumours, osteophytes, fibrous bands, surgery, sports accidents, atlantoaxial instability, disc herniation, congenital vertebral anomalies, muscle hypertrophy, vascular malformation, and chiropractic manipulation.

That belongs in this article precisely because it is unflattering. A profession that only cites the literature agreeing with it is not reading the literature.

The practical consequence is simple. Positional syncope with nystagmus is a reason to send someone for vascular assessment before anyone puts hands on their neck, not after.

What is deliberately not in this article

There is a positional manoeuvre that provokes these symptoms. It is not described here, and it should not be attempted at home or by a clinician who is not equipped to manage what happens next.

In someone who genuinely has dynamic compression of a vertebral artery, deliberately holding the provoking position is the specific thing you do not want to do. Provocation belongs in a setting with imaging and the ability to respond, not on a kitchen chair.

How the differential is actually sorted

The HINTS examination distinguishes peripheral from central causes of vertigo with high sensitivity and specificity when it is performed correctly. It has an important scope limit that gets ignored: it is validated for acute persistent vertigo with nystagmus and an otherwise normal neurological exam. It is not a test for brief positional episodes, and applying it outside its scope produces false confidence.

Vertebrobasilar insufficiency more broadly presents with nausea, vertigo, nystagmus, cerebellar signs such as unsteadiness and clumsiness, cranial nerve findings, difficulty swallowing and slurred speech. One reason it can be hard to catch early is anatomical: because of collateral circulation through the circle of Willis and other connections, both vertebral arteries generally have to be compromised before symptoms appear. A person with an anatomical variant, such as one dominant artery, has less margin.

What this means for you

1. If you fainted, the emergency department is the right first stop. Nothing here changes that.
2. If a finding was never explained, say so out loud at the follow-up. "I was told vasovagal, but my eyes do something when I put my head back" is a specific, useful sentence.
3. Ask specifically whether position was tested. Whether imaging was done with the head neutral is a fair and answerable question.
4. Do not provoke it to prove it. Reproducing the symptom is not the same as diagnosing the cause, and it carries risk.
5. Get the vascular question settled before anyone manipulates the neck. That order is not negotiable.

What we do not know

Bow Hunter's syndrome is rare, and much of the literature is case reports and small series rather than controlled studies. That means prevalence is uncertain, the true frequency of each symptom is uncertain, and there is no good evidence on how often positional syncope with nystagmus turns out to be this rather than something else. Most people with vasovagal syncope have vasovagal syncope.

The honest claim is narrow: nystagmus is not explained by a vasovagal mechanism, an unexplained finding deserves follow-up, and there exists at least one recognised, positional, imaging-elusive condition that produces the full combination. That is a reason to ask a better question, not a reason to assume a rare answer.

Reader questions

Does vasovagal syncope cause nystagmus?
No. Vasovagal syncope is a neurally mediated reflex event with a characteristic prodrome. It does not produce nystagmus or the neurological findings seen in posterior circulation problems.

Can a normal CT or MRI miss this?
Yes, if the question is positional. Rotational vertebral artery occlusion is diagnosed with dynamic angiography performed with the head in the provoking position. Static imaging is generally ineffective for detecting position-related occlusion.

What is Bow Hunter's syndrome?
Reversible compression of a vertebral artery caused by head rotation or extension, producing episodic dizziness or vertigo with possible nystagmus, tinnitus, syncope, blurred vision and nausea, typically resolving when the head returns to neutral.

Which symptoms mean I should go to an emergency department?
Fainting, double vision, slurred speech, limb weakness, other brainstem signs, inability to stand, sudden complete hearing loss, a new and unfamiliar headache, or vertical nystagmus.

Should I test the position myself to see if it happens?
No. If dynamic compression is genuinely present, holding the provoking position is the specific thing to avoid. Provocation belongs in a setting with imaging and the ability to respond.

Is neck manipulation safe if I have positional syncope?
The vascular question should be settled first. Chiropractic manipulation appears in the published etiology list for Bow Hunter's syndrome, so positional syncope with nystagmus is a reason for vascular assessment before manual treatment of the neck, not after.

Citations

1. Rotational Vertebral Artery Syndrome. StatPearls. NCBI Bookshelf. ncbi.nlm.nih.gov/books/NBK559022.
2. Vertebrobasilar Insufficiency. StatPearls. NCBI Bookshelf. ncbi.nlm.nih.gov/books/NBK482259.
3. Bow Hunter's Syndrome. Stroke. American Heart Association. doi:10.1161/STROKEAHA.121.037253.
4. Bow hunter's syndrome due to an anomalous right vertebral artery origin and contralateral absence: a case report and literature review. BMC Neurology. 2024. doi:10.1186/s12883-024-03754-5.
5. Bow Hunter's Syndrome. Vestibular Disorders Association. vestibular.org.

This article is educational and is not medical advice, and it is not a diagnosis of anyone. Syncope requires medical evaluation. If you have fainted, see a physician. If you have any of the red flag symptoms listed above, go to an emergency department. I am a chiropractor. I do not diagnose or treat vascular conditions, and nothing here should be read as a suggestion that chiropractic care treats vertebrobasilar insufficiency or any cause of syncope.