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ARTICLES: W. S. Smith, S. C. Johnston, E. J. Skalabrin, M. Weaver, P. Azari, G. W. Albers, and D. R. Gress Spinal manipulative therapy is an independent risk factor for vertebral artery dissection Neurology 2003; 60: 1424-1428 [Abstract] [Full text] [PDF]

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Spinal manipulative therapy is an independent risk factor for vertebral artery dissection

Pierre Cote, Pierre Côté, J. David Cassidy, Scott Haldeman   (26 July 2003)

Reply to Ernst, Weintraub and Cote

Wade W. Smith, MD, PhD, S. Claiborne Johston, MD, PhD   (26 July 2003)

Spinal manipulative therapy is an independent risk factor for vertebral artery dissection

Edzard E. Ernst   (26 July 2003)

Spinal manipulative therapy is an independent risk factor for vertebral artery dissection

Michael I. Weintraub   (26 July 2003)

Spinal manipulative therapy is an independent risk factor for vertebral artery dissection 26 July 2003
Pierre Cote, Institute for Work and Health 481 University Ave., Suite 800, Toronto, Ontario, Canada, M5G 2E9, Pierre Côté, J. David Cassidy, Scott Haldeman Send Correspondence to journal: Re: Spinal manipulative therapy is an independent risk factor for vertebral artery dissection pcote{at}iwh.on.ca Pierre Cote, et al.	We read with interest the article by Smith et al. [1] The authors state that spinal manipulative therapy (SMT) is strongly and independently associated with dissection of the vertebral artery leading to stroke or transient ischemic attack (TIA). These results are consistent with the only other epidemiological study on the topic. [2] One strength of this study is the attempt to control for confounding by indication as measured by neck pain before the stroke. However, several methodological issues that threaten the validity of case- control studies require clarification. The first two relate to selection bias and the third one to information bias. First, the selection of controls may explain some of the reported association between spinal manipulation (SMT) and vertebral artery dissection. By selecting controls with stoke other than dissection, the authors have selected a control series that is sicker that the case series. Our main concern is that the controls were sampled from a population that did not give rise to the cases. This is evidenced (Table 2) by the higher proportion of significant comorbidities among the control group. Several studies have reported that patients with comorbidities or poorer health status are less likely to seek chiropractic care. [3-5] Therefore, by design, the authors may have selected a control series that was less likely to receive SMT. This would artificially inflate the association between dissection leading to stroke/TIA and SMT. Second, a history of SMT to the cervical spine may have influenced the diagnosis of vertebral artery dissection and the inclusion of these cases into the registry. This “diagnostic bias” could have led to an exaggerated estimate of the effect of SMT on vertebral artery dissection. Third, recall bias cannot be ruled out. It is possible that cases with vertebral artery dissection leading to stroke or TIA were, at the time of their visit to the medical center, differentially questioned about recent SMT to the neck. The cases would therefore be more likely than controls to associate the two events and recall this at a later time. This differential recall would inflate the odds ratio and lead to biased results. We recognize the difficulty in designing and conducting epidemiologic studies of rare adverse events. However, it is important to recognize the limitations of these methodologies and to interpret the results cautiously. References: 1. Smith WS, Johnson SC, Skelabrin EJ et al. Spinal manipulative therapy is an independent risk factor for vertebral artery dissection. Neurology. 2003. 60:1424-1428. 2. Rothwell DM, Bondy SJ, Williams JI. Chiropractic manipulation and stroke: a population-based case-control study. Stroke 2001; 32:1054-1060. 3. Carey TS, Evans A, Hadler N, Kalsbeek W, Mclaughlin C, Fryer J. Care- seeking among individuals with chronic low back pain. Spine 1995; 20:312- 317. 4. Hurwitz EL, Morgenstern H. The effects of comorbidity and other factors on medical versus chiropractic care for back problems. Spine 1997; 22:2254-2264. 5. Côté P, Cassidy JD, Carroll L. The treatment of neck and low back pain: Who seeks care? Who goes where? Medical Care. 2001. 39:956-968.
Reply to Ernst, Weintraub and Cote 26 July 2003
Wade W. Smith, MD, PhD, University of California, San Francisco , S. Claiborne Johston, MD, PhD Send Correspondence to journal: Re: Reply to Ernst, Weintraub and Cote wade.smith{at}ucsfmedctr.org Wade W. Smith, MD, PhD, et al.	We appreciate the suggestions raised in these letters. Our research was directed at helping the practicing neurologist diagnose the likely causes of stroke in young patients. We chose a nested, case-controlled design to compare the profiles of two groups: those with dissections and those without dissection. Our study was not a population based study from which incidence or procedural risk could be reported, nor was it a study designed to answer what forms of spinal manipulative therapy (SMT) were found to be risky. Therefore, conclusions as to procedural risk of SMT should be left to a study designed to answer this. Our study found that patients with dissections were healthier, and were more likely to have head and neck pain and have recently visited a practitioner that performed SMT. The results should help the practicing neurologist focus their diagnostic work-up in young patients with stroke. We agree with Dr. Weintraub that a prospective evaluation of these cohorts would help eliminate concerns of recall bias, as we discussed in our article. Additionally, a prospective study would reduce concerns of “diagnostic bias” as mentioned by Dr. Cote. Since the identification of this cohort required the combined 5-year experience of two academic stroke centers, a prospective study would not be trivial. Similarly, any practical prospective trial of SMT for neck pain would likely lack sufficient power to detect what is likely an uncommon complication of SMT. We appreciate Dr. Ernst’s remarks as his predictions about criticisms from chiropractors have come true. The article was cited in over 42 newspapers- several outside of the United States- highlighting the controversy and public interest around this topic. We agree with Dr. Ernst that the true frequency of complications from SMT is unknown and that complications can be serious. Therefore, we suggest that patients should undergo informed consent prior to SMT as they do for any procedure that carries risk.
Spinal manipulative therapy is an independent risk factor for vertebral artery dissection 26 July 2003
Edzard E. Ernst, Complementary Medicine 25 Victoria Park Rd, Exeter, EX2 4NT, UK Send Correspondence to journal: Re: Spinal manipulative therapy is an independent risk factor for vertebral artery dissection edzard.ernst{at}pms.ac.uk Edzard E. Ernst	Smith et al have provided further evidence that spinal manipulation is an independent risk factor for cerebrovascular accidents. [1] Their study is important and rigorous but will undoubtedly be criticized by chiropractors because it is retrospective and deals with small samples in its sub-analyses; only two patients with vertebral artery dissection, for instance, had a stroke immediately after spinal manipulations. [1] Chiropractors have long argued that cardiovascular accidents after spinal manipulation are very rare. [2] However, after surveying UK neurologists, we discovered 35 cases of serious complications of spinal manipulation, all of which had not been previously reported. [3] Robertson mentioned an audience pool of a single US neurology conference which disclosed 360 cases of stroke not otherwise published in the medical literature. [4] This implies that there is under-reporting. There were 40 incidents of vascular accidents between 1995 and 2003 (reference list available from author). [5] Given the extreme level of under-reporting, this is a figure which should not be trivialized. Spinal manipulation is associated with serious complications of unknown frequency. It is up to those who promote (and gain from) spinal manipulation to provide convincing evidence that its risks are not greater than its benefits. References 1. Smith WS, Johnston SC, Skalabrin EJ et al. Spinal manipulative therapy is an independent risk factor for vertebral artery dissection. Neurology 2003;60:1424-1428. 2. Haldeman S, Kohlbeck FJ, McGregor M. Unpredictability of cerebrovascular ischemia associated with cervical spine manipulation. Spine 2002;27:49-55. 3. Stevinson C, Honan W, Cooke B, Ernst E. Neurological complications of cervical spine manipulation. J Roy Soc Med 2001;94:107- 110. 4. Robertson JT. Neck manipulations as a cause for stroke. Stroke 1981;12:1. 5. Ernst E. Vascular complications associated with spinal manipulation. (submitted for publication) 2003.
Spinal manipulative therapy is an independent risk factor for vertebral artery dissection 26 July 2003
Michael I. Weintraub, New York Medical College 325 South Highland Avenue, Briarcliff Manor, NY 10510 Send Correspondence to journal: Re: Spinal manipulative therapy is an independent risk factor for vertebral artery dissection miwneuro{at}pol.net Michael I. Weintraub	In their article, Smith et al [1] demonstrate that spinal manipulative therapy (SMT) is an independent risk factor for vertebral artery dissection (VAD). While this is probably true, their methodological design with dependence on recall and cooperative filling out of a questionnaire months-years later leads not only to selection and recall bias, but also possibly inaccurate data. It is well known that VAD can occur spontaneously as with trivial trauma, infections [2], hyperextension motions with yoga, dental work, beauty parlor shampoo [3] and amusement park injuries. [4] The timing may be acute or delayed with interval damage evolving over a few days. The vertebral artery is vulnerable to mechanical injury and compression at the atlanto-axial and atlanto-occipital junctions and are not age specific. Weintraub and Khoury demonstrated a unique vulnerability of the vertebral artery with simulated hyperextension by MRA and dynamic flow analysis. [5] Specifically, if a hypoplastic vertebral artery was present with flow less than 50 ml/minute (25% of cohort of 160 cases), hemodynamic changes of occlusion, slow flow and reverse flow could occur. Thus, it will be important to note the dominance (size and caliber) of the vertebral arteries involved in the dissection. Also,since 59% of the cohort (Table 1) were women, it would be important to note how often shampooing in a beauty parlor occurred within the past month. Risk stratification relying solely on cooperation and recall of information on impaired patients can only lead to unreliable conclusions. A better design leading to more accurate data could have been achieved by the authors by having a real-time study involving two to five academic stroke centers who evaluate patients for TIA/stroke. If a dissection is identified, patients and their families should be queried at that time whether or not, within the past month, infection, chiropractic neck manipulation, dental work, amusement rides, beauty parlor shampoo in hyperextended position, protracted neck movements with yoga, painting, etc. occurred. It should also look to determine if fibromuscular hyperplasia was present. It is only by reporting real-time information with a complete questionnaire regarding additional variables can the authors arrive at a more accurate cause of these hemodynamic changes. References 1. Smith WS, Johnson SC, Skabrin EJ, et al. Spinal Manipulative Therapy is an Independent Risk Factor for Vertebral Artery Dissection. Neurology 2003; 60: 1424-1428. 2. Mas JL, Bousser MG, Hasboun D, et. al. Extracranial Vertebral Artery Dissection: A Review of 13 Cases. Stroke 1987; 18: 1037-1047. 3. Weintraub, MI: Beauty Parlor Stroke Syndrome: Report of Five Cases. JAMA 1993; 269: 2085-2086. 4. Braksiak RJ, Roberts DJ: Amusement Park Injuries and Deaths. An Emerg Med. 2002; 39: 65-72. 5. Weintraub MI, Khoury A: Cerebral Hemodynamic Changes Induced by Simulated Tracheal Intubation: A Possible Role in Perioperative Stroke? MRA and Flow Analysis in 160 Cases. Stroke 1998; 29: 1644-1649.