No tie between shingles and Parkinson’s: US veterans study
Conflicting results observed in previous studies
Shingles, an infectious disease marked by a painful skin rash with blisters, wasn’t associated with an increased risk of Parkinson’s disease, according to a study of more than 1 million U.S. veterans.
“We showed no evidence of an increased risk of incident [Parkinson’s disease] after [shingles] in a large, population-based matched cohort study using data from the U.S. Veterans Health Administration,” the researchers wrote in “Herpes Zoster and Risk of Incident Parkinson’s Disease in US Veterans: A Matched Cohort Study,” which was published in Movement Disorders.
Parkinson’s is an age-related degenerative brain disorder thought to be caused by a combination of genetic susceptibility triggered by environmental factors. For decades, infectious agents have been considered a potential triggering factor for Parkinson’s and population-based studies have suggested an increased Parkinson’s risk is linked to the influenza virus, viral hepatitis, or any recent infection while in a hospital.
Shingles, also called herpes zoster, is caused by the reactivation of the varicella-zoster virus, which also causes chickenpox in young people. After an initial infection, the virus can persist in the body and remain dormant in nerve cells for years or decades, emerging in later life as shingles.
Studies that have investigated the relationship between shingles and Parkinson’s have generated conflicting results. Two Taiwanese studies have shown an increased risk, while a U.S.-based Medicare claims study indicated it was reduced.
“We therefore aimed to investigate the association between [shingles] and incident [Parkinson’s disease] risk in the largest integrated healthcare system in the U.S., the Department of Veterans Affairs,” wrote a team led by researchers at the London School of Hygiene & Tropical Medicine, in the U.K.
Matching people with, without shingles to find Parkinson’s risk
Researchers compared the risk of Parkinson’s among people with and without shingles. Up to five people without shingles were matched by age (mean, 68), sex, race/ethnicity, site of care, and calendar time to those with the skin condition.
The 198,099 patients with incident shingles had a higher prevalence of cardiovascular diseases, hypertension (high blood pressure), immunosuppression, mood disorders, and autoimmune diseases than the 976,660 people without shingles.
During follow-up, 1,779 people with shingles (0.90%) and 8,214 people without shingles (0.84%) were diagnosed with Parkinson’s disease. Based on these numbers, shingles was not associated with Parkinson’s. The findings remained the same after accounting for the use of antiviral therapies, as well as age and poor health.
In a sensitivity analysis, the team excluded outcomes within six, 12, 24 months, and five years of follow-up in case of reverse causality, or that Parkinson’s may increase the risk of shingles. The results still showed no connection between the two conditions.
“We found no evidence that [shingles] was associated with an increase in incident [Parkinson’s disease] risk in U.S. veterans overall or in any subsets of age-group or frailty, suggesting that [shingles] is unlikely to play a major role in [Parkinson’s disease] development,” the researchers said.