New evidence suggests that shingles, which can occur in individuals who previously had chicken pox, may be associated with an increased risk of stroke in the weeks to months following a shingles episode.
Shingles, or herpes zoster, which is the result of the same virus (varicella zoster virus) that causes chicken pox, affects 1 million Americans every year. Before a vaccine for shingles became available, one-third of Americans were affected with shingles in their lifetime. Shingles occurs when the dormant virus reactivates in someone who had chicken pox in the past.
The infection targets the nervous system, and can have both short-term and long-term health effects, including the hallmark painful shingles rash that may be followed by persistent nerve-related pain that can last for months to years after the rash resolves. Now, new evidence suggests that the shingles may also be associated with an increased risk of stroke in the weeks after the rash emerges.
In a study released yesterday in Clinical Infectious Diseases, researchers at the London School of Hygiene and Tropical Medicine analyzed medical records from millions of general practice patients in the United Kingdom from 1987 to 2012 and identified more than 6500 individuals with both shingles and arterial stroke during this period. When they looked at the time points at which strokes occurred in relation to the shingles episodes, they found that the rate of stroke was significantly higher during the first 6 months following a shingles episode compared with before a shingles episode (approximately 63% higher during the first month, 42% higher during the second and third months, and 23% higher during the fourth through sixth months.)
Individuals who did not receive antiviral treatment during their shingles episodes had an even higher rate of stroke compared with those who did receive such treatment. In addition, though the case numbers were smaller, individuals in whom shingles affected the trigeminal nerve, a cranial nerve that affects facial sensation, seemed to have a higher rate of stroke than those in whom other nerves were affected.
The authors suggest 2 possible mechanisms in which shingles might increase stroke risk. First, the overall higher level of inflammation in the body during a severe systemic infection causes a state in which the blood is more prone to clotting, which can lead to stroke. Second, the shingles virus can also spread into the nerves of the blood vessel walls, leading to defective blood vessels that are more likely to allow both clots and bleeding, which can lead to stroke.
This study is the first to examine the association between shingles and stroke in a time-dependent fashion, including only individuals with both shingles and stroke, and focusing on the length of time between the 2 events. Previous studies comparing the rates of stroke in individuals who had shingles with those who did not have also found higher stroke risks in persons with prior shingles, but because the characteristics of people who get shingles and those who do not may be very different, many other confounding factors could have affected the results. This approach, on the other hand, allowed patients to serve as their own controls (with the control periods being when they were outside of a 1-year period from infection), which, according to the authors, makes the association more robust.
The authors state that their findings have implications for both clinical medicine and public health, underscoring the importance of antiviral treatment for shingles as well as shingles vaccination, which, in the United States at least, remains underused.