Risk of VBA Stroke and Chiropractic Care • Cassidy et al
S181
Table 6. Odds Ratios and 95% Confidence Intervals (CI) and Accelerated and Bias Corrected Bootstrap 95% CI for Case-Crossover Estimates of the Association Between Primary Care Physician (PCP) Visits and Vertebrobasilar Stroke
Case Crossover
Age ! 45 yr
Age ! 45 yr
Exposure
Odds Ratio (95% CI) Bootstrap 95% CI Odds Ratio (95% CI) Bootstrap 95% CI Odds Ratio (95% CI) Bootstrap 95% CI
Any PCP visit 1–1 day
4.36 (3.02–6.28) 2.91 (2.25–3.77) 2.36 (1.93–2.89) 2.38 (1.99–2.86) 2.42 (2.01–2.91) 16.00 (5.35–47.86) 13.00 (5.89–28.71) 8.28 (4.86–14.10) 7.28 (4.60–11.52) 5.65 (3.88–8.22)
3.09–6.54 2.24–3.71 1.92–2.95 1.96–2.87 2.01–2.96 5.20–72.00 6.00–31.00 4.87–14.82 4.58–11.36 3.80–8.30
15.24 (4.29–54.20) 5.62 (2.56–12.36) 2.90 (1.64–5.13) 3.53 (2.09–5.97) 2.99 (1.81–4.96)
3.70–68.00 2.10–14.60 1.56–5.09 1.96–6.49 1.69–5.09
3.72 (2.52–5.50) 2.68 (2.03–3.53) 2.30 (1.85–2.85) 2.26 (1.86–2.74) 2.34 (1.92–2.85) 13.00 (4.24–39.87) 10.86 (4.56–25.83) 6.99 (3.93–12.44) 6.92 (4.20–11.40) 5.04 (3.37–7.54)
2.53–5.64 2.02–3.55 1.85–2.93 1.85–2.80 1.91–2.96 4.00–56.00 4.57–32.00 3.85–12.85 4.19–11.85 3.32–7.53
1–3 days 1–7 days 1–14 days 1–30 days
Headache or cervical PCP visit 1–1 day
*
* * *
1–3 days 1–7 days 1–14 days 1–30 days
28.00 (3.44–227.58) 20.00 (4.38–91.28) 9.46 (2.95–30.31) 12.42 (3.95–38.99)
2.86–44.00 3.59–54.74
*Unable to compute due to small numbers.
just seen only a PCP. We were not able to run a subgroup analysis on the small number of cases that just saw a chiropractor. However, subgroup analysis on the PCP cases (n " 782) that did not visit a chiropractors during the 1 month before their stroke did not change the con- clusions (data not shown). Our results should be interpreted cautiously and placed into clinical perspective. We have not ruled out neck manipulation as a potential cause of some VBA strokes. On the other hand, it is unlikely to be a major cause of these rare events. Our results suggest that the association between chiropractic care and VBA stroke found in previous studies is likely explained by present- ing symptoms attributable to vertebral artery dissection. It might also be possible that chiropractic manipulation, or even simple range of motion examination by any prac- titioner, could result in a thromboembolic event in a patient with a pre-existing vertebral dissection. Unfortu-
reliability and validity of the codes to classify headache and cervical visits to chiropractors and PCPs is not known. It is also possible that patients presenting to hospital with neurologic symptoms who have recently seen a chi- ropractor might be subjected to a more vigorous diag- nostic workup focused on VBA stroke ( i.e. , differential misclassification). 36 In this case, the predictive values of the stroke codes would be greater for cases that had seen a chiropractor and our results would underestimate the association between PCP care and VBA stroke. A major strength of our study is that exposures were measured independently of case definition and handled identically across cases and controls. However, there was some overlap between chiropractic care and PCP care. In the month before their stroke, only 16 (2.0%) of our cases had seen only a chiropractor, while 20 (2.4%) had seen both a chiropractor and PCP, and 417 (51.0%) had
Table 7. Odds Ratios and 95% Confidence Intervals (CI) and Accelerated and Bias Corrected Bootstrap 95% CI for Case-Control and Case Crossover Estimates of the Association Between the Total Number of Chiropractic (DC) and Primary Care Physician (PCP) Visits in the Month Prior to the Index Date
All Cases
Age ! 45 yr
Age ! 45 yr
Exposures
Odds Ratio (95% CI) Bootstrap 95% CI Odds Ratio (95% CI) Bootstrap 95% CI Odds Ratio (95% CI) Bootstrap 95% CI
Case control estimates Any DC visit Headache or cervical DC visit Headache or cervical PCP visit Case crossover estimates Any DC visit Any PCP visit Headache or cervical DC visit Headache or cervical PCP visit Any PCP visit
1.14 (1.02–1.27) 1.77 (1.61–1.93) 1.13 (0.98–1.30)
1.00–1.27 1.61–1.94 0.96–1.31
1.58 (1.19–2.10) 2.12 (1.58–2.84) 1.57 (1.17–2.11)
1.19–2.19 1.53–3.01 1.08–2.18
1.01 (0.86–1.17) 1.73 (1.57–1.90) 0.95 (0.77–1.18)
0.83–1.18 1.58–1.91 0.67–1.20
6.33 (4.27–9.37)
4.38–9.18
10.00 (3.26–30.63)
*
5.87 (3.85–8.95)
4.04–9.04
1.10 (0.99–1.22) 1.49 (1.36–1.63) 1.18 (1.02–1.37)
0.97–1.24 1.34–1.66 0.99–1.45
1.37 (1.10–1.70) 1.34 (1.05–1.70) 2.80 (1.43–5.48)
1.04–1.91 0.94–1.87
0.98 (0.84–1.14) 1.52 (1.38–1.67) 1.01 (0.83–1.22)
0.80–1.15 1.36–1.68 0.74–1.29
*
3.99 (2.88–5.53)
2.74–5.80
10.64 (3.45–32.78)
3.53–43.56
3.53 (2.51–4.98)
2.35–5.25
*Unable to compute due to small numbers.
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