Cervical artery dissection, imaging, trauma and causal inference.

There is little doubt that cervical artery dissection causing stroke is associated with major trauma. 1 Willis et al 2 described several cases of unstable cervical fractures through the transverse foramina, among which 46% had associated asymptomatic vertebral artery dissection. Dissection is quite probably asymptomatic in many unrecognized posttraumatic cases. Indeed, many patients in the series reported in this issue of the Journal 3 had suffered major trauma. The implication is that vertebral artery injury may be common while remaining asymptomatic. What has emerged more vociferously in the recent past is the suggestion that minor trauma can also be associated with vertebral and carotid artery dissection and further, that symptoms may be delayed from the time of the trauma. 4,5 Patients have been described with stroke or TIA and cervical artery dissection associated with neck turning, swinging a golf club, in-line skating and other sporting activities, 6 extension of the neck over a hairdresser's sink, 7 roller coasters 8 and therapeutic neck adjustment by chiropractors, physiotherapists or other practitioners. 9-12 Other techniques such as Shiatsu have been implicated. 13 Two retrospective studies suggest a significant statistical association between chiropractic neck adjustment and stroke. 14,15 The issue of " chiropractic stroke " has been covered by the Canadian media, 16 coroner's inquests have been held in Saskatchewan and Ontario and lawsuits against chiropractors have proliferated. Despite strong circumstantial reports and opinions, the quality of evidence that minor neck trauma including chiropractic neck adjustment causes vertebral or carotid artery dissection remains weak. A majority of papers are case reports or series only representing the weakest tier of clinical evidence. While these case series lend credence to the temporal association between neck adjustment and dissection, some patients suffer the hallmark neck pain of dissection prior to neck adjustment and seek chiropractic assistance for relief of their neck pain. Neck manipulation may then dislodge a preexisting thrombus. Still, the evidence to support other important factors that lead to causative inference remains modest at best. Because major trauma is clearly associated with dissection, a dose-response relationship may be implied. However, it is unclear whether more frequent episodes of minor trauma might lead to dissection. The statistical magnitude of effect for the association between chiropratic neck adjustment and subsequent stroke, characterised by odds ratios derived from retrospective case-control studies are supportive. 14 However, retrospective case-control studies are subject to many potential biases allowing for continuing uncertainty. …