Neck and spine adjustments by chiropractors and other practitioners can increase the risk of stroke, according to a study published in the May 13 issue of Neurology, the scientific journal of the American Academy of Neurology.
People under age 60 who have strokes or mini-strokes from tears in their neck arteries were six times more likely to have visited a practitioner who manipulated their neck within the past 30 days compared with people who had strokes from other causes.
Several reports have described cases of strokes occurring after cervical spine manipulation, but it's been unclear whether the cervical spine manipulation causes the tear in the artery, or dissection, or whether patients with dissections seek care because they have neck pain.
"This is the first controlled study to show that spinal manipulation is independently associated with arterial dissection, even after accounting for people who experienced neck pain before they had the adjustment," said study author and neurologist Wade S. Smith, MD, PhD, of the University of California, San Francisco.
For the study, researchers identified all patients under age 60 who had arterial dissection and stroke caused by blockage of blood flow to the brain or mini-stroke, called transient ischemic attack (TIA), over a five-year period at two stroke centers. These patients were compared to people who had strokes or TIAs from other causes during the same period. There were 51 people with stroke caused by dissection and 100 people with strokes from other causes.
Seven people with dissection had cervical spine manipulation before the stroke or mini-stroke, compared to three people without dissection. For those with dissection, the stroke occurred an average of 1.4 days after the manipulation, compared to 8.4 days for those without dissection.
Neurologist Linda S. Williams, MD, who wrote an editorial accompanying the article, noted that the study has limitations, including the recall bias that occurs in any retrospective study asking people to remember events that happened years or months before. Williams noted that researchers cannot yet precisely estimate the risk of stroke after neck manipulation.
"But the main issue is that the benefit of manipulation therapy has not been demonstrated by scientific studies," Williams said.
In the study, 57 percent of the patients with dissections said their head or neck pain increased after the manipulation.
Smith said that people with increased pain after manipulation should seek a medical evaluation immediately. "It's possible that they could have a dissection and be at risk for stroke," he said.
Smith noted that the cause of dissection is unknown in the majority of cases. Some rare medical conditions increase the likelihood of dissection. Other reported causes include trauma from motor vehicle accidents or sports injuries and even simple, sudden movements, such as coughing or lifting heavy objects.
The annual incidence of dissections is estimated at 2.6 per 100,000 people. Spontaneous dissections cause approximately 16 percent of all strokes in young people.
In a dissection, the tear in the artery allows blood to enter the wall of the artery, causing either a blood clot or an aneurysm to form, which can disrupt blood flow to the brain.