|Study title: Chiropractic care and the risk of vertebrobasilar stroke: results of a case-control study in U.S. commercial and Medicare Advantage populations
Authors: Kosloff T, Elton D, Tao J & Bannister W
Publication information: Chiropractic and Manual Therapies 2015; 23: 19.
A 2003 survey of chiropractors by the U.S. National Board of Chiropractic Examiners reported that neck conditions and headache/facial pain made up respectively 18.7 per cent and 12 per cent of their patients’ chief complaints.
Chiropractors regularly use spinal manipulative treatment (SMT) in the management of neck pain and headache, even though an association with vertebral artery dissection has been reported. SMT is used so regularly by chiropractors that visits to a chiropractor have been used as a proxy for SMT in case-control studies done by Rothwell et al. and Cassidy et al. Both of these studies reported an increased risk of vertebrobasilar (VBA) stroke associated with chiropractic visits for persons under 45 years of age. However, Cassidy et al. found the association was similar to visits to a primary care physician and suggested the association between chiropractic care and stroke was non-causal.
This study primarily aimed to replicate in a U.S. population the Cassidy et al. case-control study that was performed in a Canadian population. The Cassidy study was hailed as one of the best-designed investigations of the association between chiropractic manipulative treatment and VBA stroke. The current study also intended to compare the association with recent primary care physician (PCP) care and VBA stroke in samples of the U.S. commercial and Medicare Advantage (MA) populations.
The secondary aim of this study was to gauge the practicality of using chiropractic visits as a proxy measure for exposure to spinal manipulation.
There were 1,159 VBA stroke cases and 4,633 controls in the commercial study sample with an average age of 65.1 years and a proportion of males at 64.8 per cent. There were 670 stroke cases and 2,680 matched controls included in the MA study with an average age of 76.1 years and 58.6 per cent were male. The prevalence rate of VBA stroke in the commercial population was 0.0032 per cent and 0.021 per cent in the MA population.
A high percentage of cases had reported at least one comorbid condition (71.5 per cent in the commercial study and 88.5 per cent in the MA study). The most common comorbid conditions included hypertensive disease, ischemic heart disease, disease of pulmonary circulation, other forms of heart disease, hypercholesterolemia, and diseases of the endocrine glands.
Visits to chiropractors within 30 days prior to hospital admission occurred in 1.6 per cent of commercially insured stroke cases, as compared to 1.3 per cent of controls visiting chiropractors within 30 days prior to their index date.
Visits to a PCP within 30 days prior to the index date occurred in 18.9 per cent of the stroke cases, whereas only 6.8 per cent of controls had visited a PCP.
In the MA sample, the percentage of exposure for chiropractic visits was lower within the 30-day hazard period for cases (0.3 per cent) than for controls (0.9 per cent). On the other hand, the percentage of exposures for PCP visits was higher for cases (21.3 per cent) than for controls (12.9 per cent).
No association between chiropractic visits and VBA stroke was found for the overall sample, or when stratified by age. However, there was an association between PCP visits and VBA stroke that was present in all age groups and lengths of hazard periods.
In spite of what several other case-control studies have reported, this study found no significant association
between exposure to chiropractic care and the risk of VBA stroke. This finding strengthens the viewpoint that chiropractic care is not likely a cause of VBA strokes; then again, it does not totally exclude cervical manipulation as a possible cause or contributory factor in the occurrence of VBA stroke.
The secondary analysis showed that manipulation may or may not have been reported at every chiropractic visit. Thus, using chiropractic visits as a proxy for manipulation is not reliable.