When considering the overall groups within 30 days of the index date: • 4 per cent of cases and controls had visited a chiropractor • 53 per cent of cases and 30 per cent of controls had visited a PCP. For subjects who were under 45 years of age, within seven days of the index date: • 7.8 per cent of cases had consulted a chiropractor, compared to 3.4 per cent of controls • 24.5 per cent of cases had consulted a PCP, compared to 6.6 per cent of con- trols • overall, there was an increased as- sociation between chiropractic visits and VBA stroke regardless of the hazard pe- riod. For subjects who were 45 years of age and older: • there was no association between chiropractic visits and VBA stroke. There was an increased risk of VBA stroke regardless of the hazard period or the age of the subject in those who vis- ited a PCP in the month prior to the index date. The results of the case-control and case-crossover analyses were very similar. Strong associations were observed between PCP visits and subsequent VBA stroke, which the authors suggested was probably related to patients with head and neck pain from vertebral artery dissection who obtained care for these symptoms. This association represents an underlying intrinsic probability of patients with ver- tebral artery dissection, especially when one considers that it is not plausible that PCP care would be capable of causing a VBA stroke. The association between chiroprac- tic visits and VBA stroke was not found to be larger than the association be- tween PCP visits and VBA stroke. The authors therefore concluded that there is no excess risk of VBA stroke from chiropractic care. LIMITATIONS TOTHIS STUDY INCLUDE: • Health administrative data was used, which may lead to misclassification bias. • Not separating VBA strokes into categories of etiology, which is especially important in this context, since dissec- tion-related strokes are mainly what have been ascribed to chiropractic care. The 14 • CANADIAN CHIROPRACTOR | APRIL 2008 Pure Encapsulations is proud to announce the results of a recent survey con- ducted by Consumer Labs. Pure Encapsulations is a manufacturer of premium grade, hypoallergenic supplements for chemically and environmentally sensitive individuals. Prod- ucts are free of allergens, excipients and fillers. Ingredients are sourced from trusted industry leaders worldwide while fin- ished products are voluntarily tested by third party labs to verify purity and potency for supplements you can trust. www.canadianchiropractor.ca inclusion of cases with VBA strokes due to atherosclerotic thrombi, for instance, would tend to confound the findings of this study. The authors investigated the potential for this bias to influence the study’s conclusions using a sensitivity analysis and did not think it would. • Patients who have recently seen a chiropractor and then present to a hos- pital with neurological symptoms might receive a more thorough examination focused on VBA stroke. Thus revealing more chiropractic-related cases than PCP patients with subsequent neurological symptoms. CONCLUSIONS AND PRACTICAL APPLICATION: There is an association between VBA stroke and chiropractic visits in patients under 45 years of age. A similar associa- tion exists between VBA stroke and PCP visits in patients from all age groups. Therefore, the results of this study pro- vide no evidence of excess risk of VBA stroke associated with chiropractic care. The increased risk of VBA stroke that was found to be associated with both chi- ropractic and PCP visits is probably re- lated to patients seeking treatment of VBA dissection-related neck pain and head- ache from these providers prior to their VBA stroke. This study does a very good job of an- swering the long-standing question about why patients appear to have a higher rate of VBA stroke following chiropractic care, but because strokes have been reported to occur immediately following cervical ma- nipulation, it still appears that manipula- tion is capable of triggering a stroke in a patient with existing VBA dissection. It is not known from the Cassidy et al. study, however, what proportion of reported VBA strokes occurred under these conditions, yet given the data reported for all cases of VBA, it appears to be extremely rare. This would likely mean that any sudden or ex- treme neck movement in these patients (manipulation or some activities of daily living) is at least theoretically risky after dissection has occurred. Previous literature has indicated that there are no valid pre-manipulative tests to screen for potential VBA stoke. Practi- tioners should therefore attempt to iden- tify patients who present with active dis- sections by being alert for signs of VBA insuffi ciency, especially in those with a sudden onset of new and unusual head- ache and neck pain. Neurological signs and symptoms associated with VBA insuf- fi ciency include fainting spells, dizziness, diplopia, dysarthria, dysphagia, ataxic gait, nausea, numbness, and nystagmus. Patients with frank neurological manifes- tations of VBA insuffi ciency should not receive cervical manipulation, but should be referred for appropriate medical care, sometimes via emergency transport. • new product
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