Spontaneous Cervical Artery Dissections and Implications for Homocysteine

Dr Haynes' comments on my homocysteine study, recently published,1Rosner A Spontaenous cervical artery dissections and implications for homocysteine.J Manipulative Physiol Ther. 2004; 27: 124-132Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar are a welcome response from an individual who has made important contributions in the field of vertebral arterial patency and premanipulative testing by means of Doppler velocimetry.2Haynes MJ Vertebral arteries and cervical movement: Doppler ultrasound velocimetry for screening before manipulation.J Manipulative Physiol Ther. 2002; 25: 556-567Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar Dr Haynes' arguments concerning the noninvasiveness and safety of the procedure, the relatively low cost of the Doppler velocimeter, and what appears to be good interexaminer reliability of the instrument are well taken; however, a number of additional considerations need to be kept in mind as well:1.Actual data on the specificity and sensitivity of Doppler velocimetry vis-a-vis arterial dissection do not appear to be available, such that Haynes' argument concerning the imperfection of using a cutoff of 12.0 μmol/L of homocysteine to distinguish normal and potentially dissecting populations remains formally unanswered.2.By his own admission, Dr Haynes indicates that Doppler ultrasound is unable to detect stenoses of less then 60%; therefore, this procedure is at risk of missing the hemodynamic alterations that are associated with a small dissection.2Haynes MJ Vertebral arteries and cervical movement: Doppler ultrasound velocimetry for screening before manipulation.J Manipulative Physiol Ther. 2002; 25: 556-567Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar This raises the possibility of a false-negative result.3.In his discussions, Dr Haynes has outlined the difficulty of locating vertebral artery Doppler signals with the head in the neutral position. With the artery having a small diameter deep within the neck, there is the possibility of obtaining abnormal or absent Doppler signals from a normal artery, creating a false-positive result, especially in the early stages of learning the technique.2Haynes MJ Vertebral arteries and cervical movement: Doppler ultrasound velocimetry for screening before manipulation.J Manipulative Physiol Ther. 2002; 25: 556-567Abstract Full Text Full Text PDF PubMed Scopus (31) Google Scholar Although high sensitivity of the technique with encouraging kappa statistics have provided encouraging signs for considering this protocol for routine premanipulative testing, further data on its specificity and sensitivity for identifying arteries likely to dissect would be highly desirable. As Dr. Haynes aptly points out, the need to provide further homocysteine data to more definitively establish the risk of cervical manipulation is clearly evident as well; however, there is a now a 30-year compendium of literature associating homocysteine with the disruption of arterial and epithelial integrity which cannot be ignored:1.In one study of patients with cervical artery dissections compared with age-matched control subjects, dissecting patients determined an average homocysteine level of 17.9 μmol/L, whereas control subjects yielded just 6.0.3Gallai V Caso V Paciaroni M Cardaioli G Arning E Bottiglieri T et al.Mild hyperhomosyct(e)inemia: a possible risk factor for cervical artery dissection.Stroke. 2001; 32: 714-718Crossref PubMed Scopus (105) Google Scholar2.Perfusions of elevated levels of homocysteine in baboons resulted in patchy endothelial desquamation in the aortic surface.4Lenz SR Sobey CG Piegors DJ Bohoptakar MY Faraci FM Malinow MR et al.Vascular dysfunction in monkey with diet-induced hyperhomocysteinemia.J Clin Invest. 1996; 98: 24-29Crossref PubMed Scopus (477) Google Scholar3.In subjects with hyperhomocysteinemia, there is an impaired reaction of endothelium-dependent and flow-mediated dilation.5Woo KS Chook P Lolin YI Cheung AS Chan LT Sun YY et al.Hyperhomocysteinemia is a risk factor for endothelial dysfunction in humans.Circulation. 1997; 96: 2542-2544Crossref PubMed Scopus (461) Google Scholar4.In cell culture experiments, addition of homocysteine into the cell medium produces cell detachment from the endothelial cell monolayer.6Wall RT Harlan JM Harker LA Striker GF Homocysteine-induced endothelial cell injury in vitro: a model for the study of vascular injury.Thromb Res. 1980; 18: 113-121Abstract Full Text PDF PubMed Scopus (452) Google Scholar There is little doubt that as much useful information as possible regarding premanipulative testing needs to be conveyed to the chiropractic practitioner—as Dr Haynes has pointed out—if arterial dissections or strokes are to be avoided. However, as both the study by Schievink,7Schievink WI Current concepts: spontaneous dissection of the carotid and vertebral arteries.N Engl J Med. 2001; 344: 898-906Crossref PubMed Scopus (1255) Google Scholar which Haynes has cited, as well as my own studies1Rosner A Spontaenous cervical artery dissections and implications for homocysteine.J Manipulative Physiol Ther. 2004; 27: 124-132Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar, 8Rosner A CVA risks in perspective.Man Med. 2003; 41: 215-223Crossref Scopus (8) Google Scholar have shown, the risk of spontaneous arterial dissection that has been reported may be as much as an order of magnitude greater than the stroke rates generally attributed to chiropractic intervention.8Rosner A CVA risks in perspective.Man Med. 2003; 41: 215-223Crossref Scopus (8) Google Scholar Thus, in terms of the welfare of the patient, one needs to look beyond what Dr Haynes has proposed and try to provide the most useful information for the individual who may be at risk for an arterial dissection—whether a chiropractic patient or not. Thus, I would maintain that until a more definitive candidate for testing the population at large can be presented, the homocysteine determination should remain a consideration for adding to the patient's profile. In a perfect world, it would be included most likely by the medical physician (who in best medical practice would be screening the patient for cardiovascular risk factors anyway) in a routine physical examination of the patient. Following this scenario, there would be no additional blood-stick but simply the retrieval of data that most ideally would already have been included in a patient's background information. Furthermore, I believe that pursuing the biochemistry of the vertebral artery by means of studying homocysteine or any other metabolite levels is the best way to understand how both genetic and environmental defects may have conspired to place the vertebral arteries of certain individuals in harm's way. Certainly, one would hope for a thorough biochemical, as well as structural, examination of the circulatory system of any future patient suspected of having expired as either a direct or indirect result of spinal manipulation—a process that was outrageously thwarted recently with the disappearance of the heart of Lana Lewis, the deceased subject of the recent inquest in Toronto in which attempts were made to link a chiropractor to the death of a patient 8 days after the appointment.9Bonnell G. Chiropractic death an accident: inquest. Toronto Star; January 19, 2004.Google Scholar

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