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Date Posted:

April 2011

Study Title:

A population-based case-series of Ontario patients who develop a vertebrobasilar artery stroke after seeing a chiropractor


Choi S, Boyle E, Côté P & Cassidy JD.

Author's Affiliations:

Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada.

Publication Information:

Journal of Manipulative & Physiological Therapeutics 2011; 34:15-22.

Background Information:

Vertebrobasilar artery (VBA) stroke is a rare condition with reported incidence rates of 0.750 and 0.855 per 100,000 person-years in Ontario and Saskatchewan, Canada (respectively). Less than 50% of affected persons will experience a full recovery and some will have permanent neurological deficits. On occasion the outcome is devastating, potentially causing death (1).

Based mainly on 4 epidemiological studies and numerous case reports, it has been suggested that chiropractic cervical spine manipulation may be a cause of VBA strokes. However, more recent evidence suggests that these studies may have been influenced by selection bias, since many patients seek care from chiropractors for neck pain and headache which are often the early symptoms of an impending VBA stroke (2).

Case series and survey studies have pointed to several traits as being more likely in patients who develop VBA stroke following chiropractic care; in particular cervical manipulation. These traits include:
  1. younger than 40 years,
  2. are female, and
  3. seldom have risk factors for cardiovascular and/or cerebrovascular disease been implicated.
Case series and surveys are purely descriptive and have a number of limitations (e.g., they are subject to selection and information bias). Therefore, they cannot be used to make valid inferences about the characteristics of any condition, nor cause and effect regarding a clinical relationship between a treatment and an adverse event.

The purpose of the current study was to describe the demographics, past health care utilization, and comorbidities of VBA stroke patients in Ontario, Canada who consulted a chiropractor within one year prior to their stroke.

The authors emphasized that this study was also descriptive and that its findings could not be used to make causal inferences about the etiology of VBA stroke. They did, however, consider that its findings would help portray which individuals would be more likely to develop the condition.

Pertinent Results:

The researchers were able to identify 818 VBA stroke cases, although 32 cases had to be excluded because the patients’ ambulatory records could not be found in the OHIP (the Ontario health information system) database. Of the remaining 786 VBA stroke cases, 93 had consulted a chiropractor in the year before their stroke and were included in the sample. More specifically:
  • 87.1% (81) of the 93 patients had visited a chiropractor between 3 and 12 months before their stroke,
  • 38.7% (36) had a chiropractic visit the month before their stroke, and
  • 29.0% (27) patients had visited a chiropractor 2 weeks before their stroke.
(several patients consulted chiropractors during more than one period so these numbers do not add up to 93 cases)

There were 5,744 ambulatory records related to the 93 cases who had received chiropractic care, although 3,522 had to be excluded because they were for nonemergency hospital in-patient visits or for non-ambulatory procedures. Thirty one additional records were excluded because they were for non-direct patient care, filling out administrative forms, or group-patient therapy consultations, which left 2,191 records in the analysis.

The sample had visited medical providers during the year before their stroke as follows:
  • 95.7% to a primary care physician,
  • 78.5% had at least one specialist visit,
  • 32.3% visited an emergency department, and
  • 19.6% had an annual health examination.
Comorbidities that were most commonly present in these cases included:
  • neck pain and headache (66.7%),
  • diseases of the circulatory system (63.4%), and
  • disease of the nervous system and sense organs (47.3%).
About 75% of the patients who received chiropractic care before their stroke had at least one of the comorbidities commonly associated with stroke (e.g., hypertension, heart disease, diabetes, hypercholesteremia, cerebrovascular disease, upper respiratory tract infection, addiction, and/or obesity).

Clinical Application & Conclusions:

Previous case series and surveys of physicians have reported that VBA stroke patients are typically younger than 40 years of age and are female, whereas the mean age of the sample in this study was 57 years and there was an equal distribution between men and women.

Furthermore, earlier studies have reported that patients who saw a chiropractor before developing a VBA stroke were more likely to be healthy and less likely to have cardiovascular and cerebrovascular disease risk factors. This study, however, reported that these risk factors were common.

Regarding the potential for developing VBA stroke, the results of this study will likely lead to more confusion among practitioners who manipulate the cervical spine about which patients they should exercise caution with or possibly preclude manipulative care from. The current evidence suggests that they should be vigilant for the signs and symptoms of a developing cervical artery dissection that could lead to a VBA stoke in every patient. However, these patients are usually difficult to recognize. Terrett (3) suggested the 5 Ds and 3 Ns as a good way to screen candidates before cervical manipulation. To review, they are as follows:
  1. Diplopia – including double vision and infrequently other vision problems.
  2. Dizziness – may range in severity from unexplained lightheadedness to frank vertigo.
  3. Drop attacks – sudden weakness of the face, arm or leg which may result in a sudden, unexplained fall.
  4. Dysarthria – consisting of impaired speech and/or hoarseness.
  5. Dysphagia – difficulty swallowing.
  6. Ataxia – difficulty walking, falling or veering to the side.
  7. Nausea – may range in severity from queasiness to vomiting.
  8. Numbness – loss of sensation on one side of the body.
  9. Nystagmus – involuntary rhythmic eye movements.
Based on the overall evidence, patients who will develop VBA stroke following cervical manipulation may be young or old, male or female, and they may or may not have risk factors for cardiovascular or cerebrovascular disease. Therefore, practitioners should suspect every patient and be vigilant with them all.

Study Methods:

This was a population-based case series of patients who were hospitalized with VBA stroke during the 10 year period between April 1, 1993 and March 31, 2002. The source population was made up of all Ontario residents who were covered by the Ontario Health Insurance Plan (OHIP). All patients who suffered an acute incident VBA stroke and presented to an Ontario hospital during the specified timeframe were included in the analysis.

Eligible VBA stroke cases were identified from two databases:
  1. The Canadian Institute for Health Information’s Discharge Abstract Database.
  2. The OHIP claim database, which includes all eligible claims made by physicians, specialists, and chiropractors under Ontario's universal fee-for-services health care system.
Demographic information was obtained from the Ontario Registered Person's Database.

Cases were included if they had at least one visit to a chiropractor in the year before their VBA stroke. These individuals were considered to have used chiropractic services.

A cerebrovascular risk profile was outlined that included 8 stroke comorbidities, including hypertension, heart disease, diabetes, high cholesterol, cerebrovascular disease, upper respiratory tract infections, addiction, and obesity.

The presence of neck pain and headaches was also described since they are commonly early symptoms of VBA stroke.

Other general health conditions that were considered in the analysis were infections and parasites; neoplasms; endocrine, nutritional, and metabolic disease and immunity disorders; diseases of blood and blood-forming organs; mental disorders; diseases of nervous system and sense organs; diseases of circulatory system; diseases of respiratory system; diseases of digestive system; diseases of genitourinary system; diseases of skin and subcutaneous tissue; diseases of musculoskeletal and connective tissue; and accidents, poisonings, and violence.

Study Strengths / Weaknesses:

This was essentially a well-done study, although it has several limitations, as follows:
  1. Misclassification bias could have occurred, in which the ICD-9 codes that were used to categorize the patients as having a VBA stroke were incorrect.
  2. There was no discrimination between VBA strokes that originated from dissecting cervical arteries and those that were non-dissecting in nature.
  3. The study is an improvement on previous case series and surveys, but it was still a retrospective descriptive study that relied on insurance data.
The authors suggested that relying on information derived from case-series or surveys of health care professionals may provide a biased depiction of who develops VBA stroke.

Additional References:

  1. Dziewas, R., et al., Cervical artery dissection--clinical features, risk factors, therapy and outcome in 126 patients. J Neurol, 2003. 250(10): p. 1179-84.
  2. Cassidy JD, Boyle E, Côté P, et al. Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case-control and case-crossover study. Spine 2008;33(Suppl):S176-83.
  3. Terrett AGJ. Current concepts: Vertebrobasilar complications following spinal manipulation. West Des Moines: NCMIC Group, Inc.; 2001.

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