Cervical Artery Dissection
Chiropractic Care and Cervical Artery Dissection
In this month’s journal, I’m not actually going to present a specific study. Instead, I’m going to present a meta-analysis, in which authors pool together evidence from similar studies to test for statistical significance. Meta-analyses are great for assessing if there really is a clinical correlation or causal relationship between an intervention and a specific outcome. The actual meta-analysis that I’m reviewing was provided by Marc Abla, Executive Director of the ICS, should be a paper that Every chiropractor should have a copy of in his/her office and readily be able to provide a brief summary to patients and other healthcare providers.
Systemic Review and Meta-analysis of Chiropractic Care and Cervical Artery Dissection: No Evidence for Causation1
In this meta-analysis, the authors (who are neurosurgeons) attempt to determine if there is a causal relationship between chiropractic care (manipulation) and cervical artery dissection (CAD). Carotid artery dissection has an estimate of 2.5-3 per 100,000 and vertebral artery dissection is estimated to occur at 1-1.5 per 100,000. As you know, CAD is rare, but there have been numerous articles that have created the impression of an association between spinal manipulation and CAD. In fact, the American Heart Association recently stated in a study they conducted that an association exists.2 The authors of the meta-analysis I reviewed for this article sought to examine the strength of the evidence by performing a systematic review and evaluation of the body of evidence as a whole.
The authors used Medline and the Cochrane databases with the key terms of “chiropractic,” “spinal manipulation,” “carotid artery dissection,” “vertebral artery dissection,” and “stroke.” The articles were reviewed by the authors for inclusion and exclusion in the meta-analysis. Articles were included when they reported human trials of patients with reported carotid or vertebrobasilar artery dissection and recent chiropractic cervical manipulation. Non-English language studies were excluded. Articles were then graded by criteria established by the American Academy of Neurology.
The GRADE System
How the authors determined what statistical test to run is beyond the scope of this article, but I would encourage you to review the meta-analysis article yourself for that information. The authors used the GRADE system (formulated by the Grading of Recommendations Assessment, Development and Evaluation [short GRADE] Working Group) to evaluate the body of evidence for quality. A final GRADE designation was achieved by consensus after discussions involving all study authors as recommended by the GRADE guidelines. This particular system is designed to assess the total body of evidence, rather than one individual study. The criteria the authors use are the study design, risk of bias, inconsistency, indirectness, imprecision, publication bias, effect size, dose-response, and all plausible residual confounding. A confounding relationship is a variable that correlates with both the independent and dependent variables. After “GRADEing,” the four possible designations for the articles are high, moderate, low and very low, referring to the quality of evidence on a specific outcome.
The authors pulled 253 articles and decided to use only Class II and III studies (6 total). Using combined data of Class II and III studies suggested an association between dissection and chiropractic care. Using only Class III studies, there again appeared to be a “small” association between CAD and chiropractic care.
Included in this article, the authors gave a brief description of each study included in their meta-analysis. They also described some of the major limitations that were common in the studies, which included the use of health administrative databases. These databases depend upon accurate ICD coding, which could introduce misclassification bias. Also, the articles do not note what type of spinal manipulation is being performed, and the use of retrospective data may introduce recall bias when a survey or interview is used. As stated in the meta-analysis, “Moreover, patients arriving at a hospital complaining of neck pain and describing a recent visit to a chiropractor may be subject to a more rigorous evaluation for CAD (interview bias).” Lastly, substantial variability occurred among the diagnostic procedures performed.
The Relationship Betweem CAD and Chiropractic Manipulation is Very Low
Using the GRADE system, the authors concluded that the quality of the body of evidence about a possible relationship CAD and chiropractic manipulation is very low. The reasoning for this rating was due to most studies being observational, the potential for bias, the body of evidence was derived from measures of association, and, lastly, the potential confounder of neck pain would increase, rather than reduce, the hypothesized effect. For clarification regarding the confounder of neck pain, neck pain correlates to both CAD (independent variable) and manipulation (dependent variable).
80% of patients with CAD report neck pain.3 Patients with neck pain, however, often see a chiropractor for treatment, which typically involves manipulation. If a patient who has neck pain related to an active CAD presents to a chiropractor, that patient will likely receive manipulation if there are no contraindicating “red flags.” Therefore, did the chiropractor cause the CAD? It is very difficult to answer this question affirmatively due to the relationship of neck pain with CAD. The authors, therefore, conclude that there is no causal relationship between chiropractic care and CAD.
The authors start their conclusion by stating that, “The greatest threat to the reliability of any conclusions drawn from these data is that together they describe a correlation but not a causal relationship, and any unmeasured variable is a potential confounder.” A prospective, randomized study is the best design to control for confounders, but due to the rarity of CAD and ethical implications, it would be difficult to undertake such a study.
It is very refreshing to see an article such as this in the literature, and I am extremely grateful that Marc Abla shared it. The reality is that I answer weekly, “Does an adjustment cause stroke?” This article is a great resource for any DC who will be answering this question, especially to the medical community. I strongly recommend that we all read and familiarize ourselves with this article in its entirety.
- Church E W, Sieg E P, Zalatimo O, et al. (February 16, 2016) Systematic Review and Meta-analysis of Chiropractic Care and CervicalArtery Dissection: No Evidence for Causation. Cureus 8(2): e498. DOI 10.7759/cureus.498
- 11. Biller J, Saccro RL, Albuquerque FC, et al. Cervical Arterial dissections and association with cervical manipulative therapy: a statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2014, 45:3155-3174.
- Lee VH, Brown RD Jr, Mandrekar JN, et al. Incidence and outcome of cervical artery dissection: a population-based study. Neurology. 2006, 67:1809-1812.