S178 Spine • Volume 33 • Number 4S • 2008
Exposures All reimbursed ambulatory encounters with chiropractors and PCPs were extracted for the one-year period before the index date from the OHIP database. Neck-related chiropractic visits were identified using diagnostic codes: C01–C06, cervical and cervicothoracic subluxation; C13–C15, multiple site subluxa- tion; C30, cervical sprain/strain; C40, cervical neuritis/ neuralgia; C44, arm neuritis/neuralgia; C50, brachial radiculi- tis; C51, cervical radiculitis; and C60, headache. For PCP visits, we included community medicine physicians if they submitted ambulatory fee codes to OHIP. Fee codes for group therapy and signing forms were excluded. Headache or neck pain- related PCP visits were identified using the diagnostic codes: ICD-9307, tension headaches; 346, migraine headaches; 722, intervertebral disc disorders; 780, headache, except tension headache and migraine; 729, fibrositis, myositis and muscular rheumatism; and 847, whiplash, sprain/strain and other trau- mas associated with neck (These codes include other diagnoses, and we list only those relevant to neck pain or headache). There is no limit on the number of reimbursed PCP visits per year. However, there are limits chiropractors, but less than 15% of patients surpass them. 24 Statistical Analysis Conditional logistic regression was used to estimate the asso- ciation between VBA stroke after chiropractor and PCP visits. Separate models were built using different a priori specified hazard periods, stratified by age ( ! 45 years and ! 45 years) and by visits with or without head and neck pain related diag- nostic codes. For the chiropractic analysis, the index date was included in the hazard period, since chiropractic treatment might cause immediate stroke and patients would not normally consult a chiropractor after having a stroke. However, the in- dex day was excluded from the PCP analysis, since patients might consult these physicians after experiencing a stroke. We tested different hazard periods, including 1 day, 3 days, 1 week, 2 weeks, and 1 month before the index date. Exposure occurred if any chiropractic or PCP visits were recorded during the des- ignated hazard periods. We also measured the effect of cumulative numbers of chi- ropractic and PCP visits in the month before the index date by computing the odds ratio for each incremental visit. These es- timates were similarly stratified by age and by diagnostic codes related to headache and/or neck pain. Finally, we conducted analyses to determine if our results were sensitive to chiroprac- tic and PCP visits related to neck complaints and headaches. We report our results as odds ratios (OR) and 95% confidence intervals. Confidence intervals were estimated by accelerated bias corrected bootstraps with 2000 replications using the vari- ance-covariance method. 33 All statistical analyses were per- formed using STATA/SE version 9.2. 34 Results A total of 818 VBA strokes met our inclusion/exclusion criteria over the 9 year inception period. Of the 3272 matched control subjects, 31 were excluded because of prior stroke, one had died before the index date and 76 were receiving long-term care. Thus, 3164 control sub- jects were matched to the cases. The mean age of cases and controls was 63 years at the index date and 63% were male. Cases had a higher proportion of comorbid conditions (Table 1). Of the 818 stroke cases, 337
Table 1. Age, Sex, and Comorbid* Condition of Cases and Controls Variable Cases (n " 818) Controls (n " 3164)
Age: mean, median (SD)†
63.1, 66 (15.5)
62.6, 65 (15.4) 2022 (63.9)
Males: n (%)
518 (63.3) 276 (33.7) 275 (33.6) 155 (19.0) 62 (7.6) 515 (63.0)
Hypertension*: n (%) Heart Disease*: n (%) Diabetes*: n (%) High Cholesterol*: n (%) At least one comorbid condition§: n (%)
738 (23.3) 506 (16.0) 247 (7.8) 200 (6.3) 1294 (40.9)
*Comorbid conditions determined by ambulatory diagnostic codes from the Ontario Health Insurance Plan (OHIP) during year prior to index date. †SD is standard deviation. §Indicates the presence of at least one of hypertension, heart disease, diabe- tes or high cholesterol.
(41.2%) were coded as basilar occlusion and stenosis, 443 (54.2%) as vertebral occlusion and stenosis and 38 (4.7%) had both codes. Overall, 4% of cases and controls had visited a chiro- practor within 30 days of the index date, while 53% of cases and 30% of controls had visited a PCP within that time (Table 2). For those under 45 years of age, 8 cases (7.8%) had consulted a chiropractor within 7 days of the index date, compared to 14 (3.4%) of controls. For PCPs, 25 cases (24.5%) under 45 years of age had a consultation within 7 days of the index date, com- pared to 27 (6.6%) of controls. With respect to the number of visits within 1 month of the index date, 7.8% of cases under the age of 45 years had three or more chiropractic visits, whereas 5.9% had three or more PCP visits (Table 2). The case control and case crossover analyses gave sim- ilar results. (Tables 3–7) Age modified the effect of chi- ropractic visits on the risk of VBA stroke. For those un- der 45 years of age, there was an increased association between chiropractic visits and VBA stroke regardless of the hazard period. For those 45 years of age and older, there was no association. Each chiropractic visit in the month before the index date was associated with an in- creased risk of VBA stroke in those under 45 years of age (OR 1.37; 95% CI 1.04–1.91 from the case crossover analysis) (Table 7). We were not able to estimate boot- strap confidence intervals in some cases because of sparse data. Similarly, we found that visiting a PCP in the month before the index date was associated with an increased risk of VBA stroke regardless of the hazard period, or the age of the subject. Each PCP visit in the month before the stroke was associated with an increased risk of VBA stroke both in those under 45 years of age (OR 1.34; 95%CI 0.94–1.87 from the case crossover analysis) and 45 years and older (OR 1.52; 95% CI 1.36–1.67 from the case crossover analysis) (Table 7). Our results were sensitive to chiropractic and PCP visits related to neck complaints and headaches, and we observed sharp increases in the associations when re- stricting the analyses to these visits (Tables 3–7). Overall,
Made with FlippingBook HTML5