Researchers found that people who developed shingles had four times the risk of being diagnosed with MS within the following year, relative to people who had never experienced shingles.
Shingles is a painful condition caused by a reactivation of the virus that causes chickenpox, known as varicella-zoster virus.
Once a person has had chickenpox, the virus goes into a dormant state, dwelling in the body's nerve fibers. However, in some people, the virus can reactivate and cause shingles.
Shingles usually begins with a burning pain or itch in one location on one side of the body, followed by a rash of fluid-filled blisters.
MS occurs when the protective coating around nerve fibers begins to break down—slowing the brain's communication to the rest of the body. Symptoms include fatigue and problems with balance and muscle coordination, as well as memory loss and trouble with logical thinking in some people.
About 2.5 million people have MS worldwide, according to the Multiple Sclerosis Association of America. Most experience their first symptoms between the ages of 15 and 50. Shingles occurs most commonly in the elderly, but is not uncommon in younger people, study author Dr. Jiunn-Horng Kang at Taipei Medical University Hospital told Reuters Health.
Especially those with a compromised immune system, or those under stress or taking certain drugs, are at risk.
Indeed, in the current study, approximately 100,000 people with shingles were younger than 45. Reviewing a database from the insurer that covers 98 percent of Taiwan's population, the researchers found more than 300,000 people with shingles. They compared them to nearly 950,000 others with similar characteristics, who didn't have the disease.
Over the course of a year, fewer than one in 10,000 in the group with shingles developed MS—three times as many as in the group without shingles.
This study does not show that shingles itself can cause MS, although there are "several potential mechanisms" that could explain why the two diseases are linked, Kang explained. For instance, shingles is associated with disruptions to the immune system, which in turn might trigger MS, Kang said.
Also, a reactivation of the shingles virus may "provoke a series of immune responses in the host which may be linked to MS," the researcher suggested.
In the Journal of Infectious Diseases, the researchers caution that most people included in the study are Han Chinese, among whom MS occurs relatively infrequently, so the findings may not apply to Western populations.
What's more, the authors did not have information about whether people smoked or drank alcohol, which could influence the findings.
"These factors may be confounding to our results and need to be further explored," Kang noted.
In an editorial, Dr. Teresa Corona at the Instituto Nacional de Neurología y Neurocirugía in Mexico and a colleague note that the results are clear, but "should be corroborated in other parts of the world."