New Study Assesses Risk of Stroke And Cervical Manipulation
By John Reggars DC, MChiroSc.

This rather unique study, published in the prestigious journal Spine and co-authored by noted Canadian chiropractor and researcher David Cassidy¹, attempted to estimate the risk of vertebrobasilar stroke (VBS) associated with chiropractic visits and general medical practice visits.

This study suggests that the risk of stroke associated with patients receiving spinal manipulation is no greater than those patients receiving primary medical care. However, the results must be interpreted with extreme caution. Various media reports and individual observers have misinterpreted the results of this study and claims that this study shows that chiropractic manipulation does not cause VBS are fanciful, false and misleading.

In summary, Cassidy et al undertook population-based case-control and case-crossover studies, where they looked at all residents of Ontario over a period of nine years and who were covered by the publicly funded Ontario Health Insurance Plan. The researchers looked at all vertebrobasilar (VBA) occlusion and stenosis strokes admitted to hospitals in Ontario for that period but excluded from the study people who had been admitted to hospital with stroke or stroke-like symptoms before the commencement of the study period. So in effect they were looking for new acute strokes related to the vertebral arteries in that 9 year period. In total 818 VBA strokes were identified.

The researchers then looked at any treatment these stroke victims had received for the 12 months preceding the stroke. As both chiropractic and medical treatments are coded and publicly funded in Ontario the type of condition being treated for each patient could be retrieved and analysed. Diagnoses by chiropractors included codes for subluxation, sprain/strain/neuritis, neuralgia, headache etc. while the medical practitioner codes included those for headache, migraine, whiplash, sprain/strain, neck pain etc.

In total, for those subjects under 45 years of age, 8 cases of stroke had consulted a chiropractor within 7 days of the index date while 25 cases of stroke had consulted their general practitioner within 7 days of their index date.

After all the data was analysed the researchers concluded that although visiting a chiropractor in the month before the index date increased the association between chiropractic visits and VBA stroke, so did visiting the general practitioner one month before the index date. The conclusion was that there was no evidence of excess risk of VBA stroke associated with chiropractic care compared to primary medical care. According to the researchers these results suggest that, at least in some of these cases, patients were seeking treatment for head and neck pain from both chiropractors and medical doctors, which was due to and undetected vertebral artery dissection and which subsequently resulted in a stroke.

If you were to just read the conclusion contained in this study’s Abstract and were to read some of the press releases and reviews, which accompanied the publication of this study; you could be forgiven for thinking that at last we have proof that cervical manipulation does not cause vertebral artery dissection and stroke. And that at worse cervical manipulation could merely aggravate an already dissecting vertebral artery. But you would be wrong as there are a few caveats that need to be recognised when interpreting the results of this study.

It must be remembered that this study was a retrospective case study and therefore no cause and effect relationship can be deduced from the results. It is well worth remembering that in previous retrospective studies on the relationship between cervical manipulation and stroke; where others have argued, that cervical manipulation caused strokes; the chiropractic profession in its defence, always put forward the argument that no cause and effect relationship could be concluded from this type of study. That argument of defence was sound but equally that argument also applies to this study. From any retrospective case study we cannot determine either way whether cervical manipulation causes vertebral artery dissection or not. The authors of this study state, “Our results should be interpreted cautiously and placed into clinical perspective. We have not ruled out neck manipulation as a potential cause of some VBA strokes.”

In the same month that the Cassidy study was published another study was published in the journal Neurologist.² This study addressed several questions including, “Does cervical manipulative therapy (CMT) cause vertebral artery dissection (VAD) and subsequent ischemic stroke?” The questions were addressed with a structured evidence-based clinical neurologic practice review and involved neuroscience students, neurologists, epidemiologists, librarians and clinical experts. This group conducted a literature review and performed critical appraisals, synthesised the results, summarised the evidence, provided commentary and declared bottom line conclusions. This group concluded that there was weak to moderately strong evidence that CMT caused VAD and associated stroke.

Further, the Cassidy study has its limitations. The authors admit that the use of health administrative data can be misleading due to misclassification bias and not all VBA strokes are secondary to vertebral artery dissection. Also because subluxation was used as a diagnostic code we do not know whether all the patients who suffered stroke after chiropractic treatment had neck pain or headache. As many chiropractors would diagnose subluxation on the basis of restricted range of motion or palpation only. Therefore, it may well be that certain patients who showed no signs of any arterial dissection still suffered a VBA stroke after manipulation. This argument has support in the literature, such as in cases where patients suffered a stroke after attending a chiropractor for the treatment of low back pain and their chiropractor elected to manipulate their neck. Furthermore, we do not know what treatment each group received from the doctor or the chiropractor. Did the doctor manipulate, did the chiropractor manipulate?

On the other hand, from a personal perspective I would tend to agree with the authors that, at least in part, this study does point to the fact that some patients who present to chiropractors with neck pain and headache are in fact experiencing the symptoms of a dissecting vertebral artery. The subsequent manipulation dislodges a clot or arterial fragment, which then travels up the arterial tree lodging itself in one of the smaller arteries and causing a stroke.

However, this explanation does not account for all manipulation associated strokes. The literature is full of examples of people experiencing VBA stroke from trivial trauma, backing their car, having their hair washed, painting the ceiling etc. It seems patently obvious to me that if these activities could result in VBA stroke then certainly cervical manipulation could do the same. Most people who experience stroke from this type of activity or trivial trauma have no identifying risk factors, signs and symptoms of impending stroke. It is thought that they have a predisposition to VBA stroke due to some yet unidentified arteriopathy, most probably some sort of connective tissue disease.

The problem for us as chiropractors or osteopaths, is that we don’t know who these people are and at present have no know way of finding out, so it is inevitable that some will seek out a chiropractor or osteopath for cervical manipulation and suffer a stroke.

But we may be able to identify some of those who like this study suggests are in the process of dissection. It is possible, that a carefully directed and thorough clinical history, plus an appropriate clinical examination may yield some clues, to the astute clinician, that the person they are examining is not a candidate for spinal manipulation and may in fact require immediate medical referral.

COCA’s Risk Management Module III has been designed specifically for this purpose and I would urge all COCA members to complete this free risk management program.

Also, a new study published in Manual Therapy and co-authored by Newcastle chiropractor and researcher Dr. Philip Bolton shows that it may be possible via the use of Doppler imaging to examine the blood flow in a patient’s vertebral artery in a clinical setting prior to spinal manipulation.³

As we already know the standard provocative tests used by chiropractors and osteopaths for vertebrobasilar ischemia, such as Maigne’s test, have poor sensitivity and specificity. The researchers suggest, that although further testing is required, it may be possible to perform a relatively simple test on the vertebral artery flow using a hand-held velocimeter, to objectively identify abnormal blood flow. If this device fulfils its potential it may be possible for the average chiropractor or osteopath to identify that group of patients whose vertebral artery flow is abnormal and in whom spinal manipulation would be contraindicated. Furthermore, this test may also identify some patients whose vertebral artery flow has been compromised by a dissecting aneurysm or blood clot and who require immediate medical referral.

The take home message here is, strokes associated with cervical manipulation do occur. Yes they may be rare but do you won’t to be the chiropractor or osteopath ordering the ambulance for one of your patients. If you use cervical manipulation in your practice do so in conjunction with the best available risk management approach. COCA’s Risk Management Module III can be downloaded free for COCA members or for $110 for non-members. www.coca.com.au/education/riskmanagementIII.asp

References:

1. Cassidy JD et al. Risk of vertebrobasilar stroke and chiropractic care. Spine 2008;33(45):176-83.
2. Miley ML, Wellik KE, Wingerchuk DM, DEmaerschalk BM. Does cervical manipulative therapy cause vertebral artery dissection and stroke. Neurologist 2008;14(1):66-73.
3. Thomas JC, Rivett DA, Bolton PS. Pre-manipulative testing and the use of the velocimeter. Man Therapy 2008;13:29-36.