Protopathic Bias and the Different Strokes

Several times when I practiced in America, I had patients who would tingle my Spidey sense:

They would come in and present with a headache and neck pain (standard) and maybe a little bit of dizziness.  But something didn’t seem right.

“It’s probably not a big deal, but I would recommend you get this checked out by an MD before coming back.”

“No, its cool, I had the same thing several years back where this Chiropractor popped my neck into place, and it went away.”

Right off the bat I’m worried because this guy wants INSTANT results and his commitment to his health goes so far as “when he needs it”, by his own perception.  

After dismissing the patient, who usually leaves in a huff, I will return any money (not that I’m required), and make a note that I referred them to an MD.  But I know right where they are going: Down the street to another Chiropractor.  

More than likely I’m out $100 and some Chiropractor is the hero who “cured” his patient.  Another possible, if not less likely, outcome is the patient, with unrealistic expectations, leaves without palliative relief feeling he was “jipped” by a “bad” chiropractor, who wasn’t as good as that other Chiropractor who “cured” him in one magical visit.

But there is another possibility, one extremely rare, but shouted from the rooftops when it does occur:  The Chiropractic patient suffers a stroke.

The most famous case of Chiropractic Stroke in recent memory was Playboy and Instagram Model Katie May who had died in her early 30’s after a Chiropractic adjustment.  May was experiencing neck pain which prompted her to go to a Chiropractor.  Despite feeling mild relief, she eventually worsened and checked into a hospital where she passed away.

Due to the words of the LA County coroner millions seized upon the heartbreak of losing a celebrity to blame the chiropractor for causing the stroke.  It was difficult not to with the coroner’s report:

“Los Angeles Assistant Chief Coroner Ed Winter tells PEOPLE that a chiropractor shifted May’s neck, tearing her left vertebral artery. The tear blocked blood flow to May’s brain and caused the stroke.”

“I personally have not seen this before,” Dr. Winter told People. 

Dr. Winter is not alone in having never seen a tearing of the vertebral artery caused by a Chiropractic adjustment.

No One Has.  It’s literally (In the correct usage of the word) impossible to tear a vertebral artery with a Chiropractic adjustment.

The best research, most of which was done in the past decade, shows that cervical spinal manipulation (CSM) performed by a chiropractor does not cause nearly enough stress on the vertebral arteries. Normal neck range of motion actually stresses the arteries more than CSM. [I,II,III,IV,V,VI,VII,VIII,IX]

Research on blood flow through the vertebral arteries during neck range of motion and during CSM demonstrates “no significant changes in blood flow or velocity in the vertebral arteries” during the procedures[X]

In a 2015 study, Buzzatti was able to measure the movement of the atlas and axis in motion during CSM and their work reinforced earlier findings of several other studies that CSM does not endanger the spinal cord and vertebral arteries any more than an active rotation of the head. [XI]

If Katie May, a healthy young woman died of a stroke that the LA County coroner attributes to the scientifically impossible, then what occurred in this tragedy?

May presented to the Chiropractor with neck pain, an extremely common condition that presents in chiropractic offices. It’s also an early warning sign of Stroke and a host of other potential afflictions.

This vague symptomatology is one of the reasons that Strokes are missed throughout the medical community, and early intervention is often too late. [XII]

The dissection that Katie May had, the vertebral artery, is rare but it does happen: Spontaneous vertebral artery dissections occur 1/100,000 persons per year while spontaneous carotid artery dissections occur 2/100,000 persons per year. [XIII]

Cervical artery dissections mainly occur spontaneously, and trauma is not required. Fukuhara studied 83 cases of patients suffering spontaneous dissections. Their dissections were discovered when they began to suffer neurological symptoms, as previous symptoms involved the patients mainly having headache and/or neck pain, the same condition that brought Katie May to seek out a Chiropractor. (73%) [XIV]

Furthermore, research says that even in the event of an already desiccated artery, manipulation by a Chiropractor can NOT make the condition worse. A series of studies on dogs with man-made injuries to the vertebral arteries found that manipulation was incapable of expanding the size of those injuries, suggesting that May’s chiropractor did not even make her condition worse. [XV, XVI, XVII]

May presented to a Chiropractor just as my patients had presented to me and just as millions of patients presented to a Chiropractor every year, with vague symptomology of neck pain, of which some are strokes that are luckily caught early and before intervention. The literature even mentions recognition inside a Chiropractors office BEFORE an adjustment. [XVIII] 

Even Medical intervention sought at an MD’s office instead of a Chiropractors office might not have staved off May’s grim fate. In the 2008 “Cassidy Study”, in research covering 9 years and 109 million person-years of observation that the incidence of persons having a vertebrobasilar injury (VBI) and stroke following chiropractic physician exposure was identical to the exposure to a general medical practitioner. Another way of saying that is walking into an MD’s office carries the same risk of a stroke as walking into a Chiropractors office, but since Medical Doctors do not adjust there is no increased danger in whatever intervention occurs in the Chiropractors office (i.e. The Chiropractic adjustment). [XIX]

Another way of articulating this:  People presenting with early signs of a stroke which are common in many other conditions, neck pain and headaches, seek medical intervention in either a Medical doctor or Chiropractors office.  While both practitioners may correctly diagnose the stroke in progress and rapidly refer the patient to emergency medical personnel, all too often either practitioner may render medical treatment specific to their specialty. These rendered treatments do nothing to alleviate the occurring stroke. 

However, there is a bias against chiropractors who are assumed to have caused a stroke which is already in progress.  This classic confuddling of Causation/Correlation has a specific term in the world of scientific research: Protopathic bias. Protopathic bias, also called “Reverse Causality”, is when an assumption is made of a treatment causing a previously undiscovered affliction before a proper diagnosis is made.  A Classic example is the use of analgesics in response to pain caused by an undiagnosed tumor, leading to the erroneous conclusion that the analgesic caused the newly diagnosed tumor. Applied to Chiropractic: we are not causing the strokes; we are failing to diagnose them. 

In a 2016 study conducted by a team of neurosurgeons from Penn State Hershey Medical Center and Johns Hopkins University School of Medicine determined stated that the belief in a causal link between CAD and CSM may inappropriately lead to episodes of litigation as a negative consequence. there was “no convincing evidence to support a causal link between chiropractic manipulation and CAD (cervical artery disease). They stated in their article, that there is significant bias in the literature against CSM and this bias leads to litigation against chiropractors. [XX] 

This bias is quite frankly detrimental not only to the perception of Chiropractic to the public, but dangerous to the public itself when the rare instances of strokes present in our office.  Separate from medical training of any particular practitioner we all appeal to the eternal human virtue of hope that we are “on the right track”, and that the medical intervention we just did will bring palliative relief soon enough to a patient. The association with Chiropractors and strokes may prevent chiropractors from making the appropriate referral once they initiate ANY intervention which will ignorantly be believed to have caused the stroke, a bias Medical Doctors do not have hanging over them like a Sword of Damocles.


[I] Piper, Howarth, Triano, Herzog Quantifying strain in the vertebral artery with simultaneous motion analysis of the head and neck: A preliminary investigation.  Clinical Biomechanics 29 (2014) 1099–1107

[II] Symons B, Herzog W. Cervical artery dissection: a biomechanical perspective. J Can Chiropr Assoc. 2013 Dec;57(4):276–8.

[III] Herzog W, Tang C, Leonard T. Internal Carotid Artery Strains During High-Speed, Low-Amplitude Spinal Manipulations of the Neck. J Manipulative Physiol Ther. 2012 Nov 6.

[IV] Herzog W, Leonard TR, Symons B, Tang C, Wuest S. Vertebral artery strains during high-speed, low amplitude cervical spinal manipulation. J Electromyogr Kinesiol. 2012 Apr 5.

[V] Symons B, Wuest S, Leonard T, Herzog W. Biomechanical characterization of cervical spinal manipulation in living subjects and cadavers. J Electromyogr Kinesiol. 2012 Mar 6.

[VI] Herzog W. Response to letter to editor by Drs. Haynes and Vincent. J Electromyogr Kinesiol. 2012;22(6):1018.

[VII] Wuest S, Symons B, Leonard T, Herzog W. Preliminary report: biomechanics of vertebral artery segments C1-C6 during cervical spinal manipulation. J Manipulative Physiol Ther. 2010 May;33(4):273–8.

[VIII] Austin N, DiFrancesco LM, Herzog W. Microstructural damage in arterial tissue exposed to repeated tensile strains. J Manipulative Physiol Ther. 2010 Jan;33(1):14–9.

[IX] Symons BP, Leonard T, Herzog W. Internal forces sustained by the vertebral artery during spinal manipulative therapy. J Manipulative Physiol Ther. 2002 Oct;25(8):504–10. 

[X] Quesnelle, Triano, Noseworthy, and Wells. Changes in Vertebral Artery Blood Flow Following Various Head Positions and Cervical Spine Manipulation. JMPT 2014, 37(1), 22-30

[XI]Buzzatti, Provyn, Van Roy, and Cattrysse. Atlanto-Axial facet displacement during rotational high-velocity low amplitude thrust: An in vitro 3D kinematic Analysis. Musculoskeletal Science and Practice. December 2015, Volume 20, Issue 6, pages 783-789.

[XII] Newman-Toker DE, Moy E, Valente E, Coffey R, Hines AL. Missed diagnosis of stroke in the emergency department: a cross-sectional analysis of a large population-based sample. Diagnosis. 2014;1(2).

[XIII] Lee, Brown, Mandrekar, Mokri. Incidence and outcome of cervical artery dissection A population-based study. Neurology (67) 2006. 1809-1812

[XIV] Fukahara, Ogata, Ouma, Tsugawa, Matsumoto, Abe, Higashi, Inoue, Tsuboi. Impact of initial symptom for accurate diagnosis of vertebral artery dissection. World Stroke Organization 2015, (10) 30-33

[XV] Kawchuk GN, Jhangri GS, Hurwitz EL, Wynd S, Haldeman S, Hill MD. The relation between the spatial distribution of vertebral artery compromise and exposure to cervical manipulation. J Neurol. 2008 Mar;255(3):371–7.

[XVI] Wynd S, Anderson T, Kawchuk GN. Effect of cervical spine manipulation on a pre-existing vascular lesion within the canine vertebral artery. Cerebrovasc Dis. 2008;26(3):304–9.

[XVII] Kawchuk GN, Wynd S, Anderson T. Defining the effect of cervical manipulation on vertebral artery integrity: establishment of an animal model. J Manipulative Physiol Ther. 2004 Nov-Dec;27(9):539–46. 

[XVIII] Mattox R, Smith LW, Kettner NW. Recognition of Spontaneous Vertebral Artery Dissection Preempting Spinal Manipulative Therapy: A Patient Presenting With Neck Pain and Headache for Chiropractic Care. J Chiropr Med.; 2014 Jun;13(2):90–5.

[XIX]Cassidy JD, Boyle E, Côté P, He Y, Hogg-Johnson S, Silver FL, et al. Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case-control and case-crossover study. Spine. 2008 Feb 15;33(4 Suppl): S176–83.

[XX] Church, Seig, Zalatimo, Hussain, Clantz, and Harbaugh. Systematic review and Meta-Analysis of chiropractic care and cervical artery dissection: No Evidence for Causation. 2016 Cureus 8(2): e498

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