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CMT & Risk of Stroke
There exists no scientific data that would suggest that chiropractic care causes any higher incidence of stroke than a typical visit to a primary care physician (PCP). Studies have shown that any observed association between Vertebral Arterial Dissection (VAD) and stroke with CMT is likely attributed to patients with an undiagnosed VAD who seek care for neck pain and headache before the onset of a stroke. 
A population-based, case-control study done by Rothwell et al confirmed an increased risk of VAD within a week of a chiropractic visit among persons under age 45 years.  However, the Neck Pain Task Force, part of the international Bone and Joint Decade accepted the study by Cassidy et al which extended these findings and found a similar risk of this form of stroke after patients visited a PCP or a doctor of chiropractic. 
Cassidy et al studied data over a period of nine years which included eligible persons admitted to Ontario hospitals following a vertebrobasilar artery (VBA) stroke and found that only 818 cases of VBA stroke were reported over 100 million person-years of data -- and many of these patients had not seen a doctor of chiropractic at all. In the data analyzed, positive associations were found between PCP visits and VBA stroke in all age groups. The study suggests that the association between chiropractic care and VBA stroke is likely due to presenting symptoms associated with VAD and that even simple range of motion examinations by a PCP could result in a thromboembolic event in a patient with presenting VAD symptoms. Researchers concluded that there exists a similar association between PCP and chiropractic visits and VBA stroke which suggests that patients with undiagnosed VAD seek care for headache and neck pain prior to the onset of a VBA stroke. 
Studies have further shown that the occurrence of VAD and stroke is extremely rare with or without any form of care. Haldeman et al analyzed data from a malpractice review evaluating all claims of stroke following chiropractic care during a 10-year period between 1988 and 1997. Approximately 134.5 million cervical manipulations were performed by doctors of chiropractic during this time. The authors found there were 43 cases of neurological symptoms following cervical manipulation over the 10-year period, 20 of which were minor and were not diagnosed as stroke by a neurologist. Twenty-three cases of stroke or vertebral artery dissection following cervical manipulation were reported. The authors concluded that there exists only a one-in-5.85-million risk that a chiropractic neck manipulation may be associated with subsequent cervical artery dissections and stroke. 
- Cassidy, JD; Boyle, E; et al. (2008). "Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case control and case crossover study". Spine 33 (Suppl1): S176-S183.
- Rothwell, DM; Bondy, SJ; Williams, JI (2001). "Chiropractic manipulation and stroke: a population-based case-control study". Stroke 32: 1054–60.
- Haldeman, S; Carey, P; Townsend, M; Papadopoulos, C (Oct). "Arterial dissections following cervical manipulation: the chiropractic experience.". CMAJ 2 (165(7)): 905-6.