LONDON — Some researchers have postulated for years that systemic infections are associated with development of Parkinson’s disease (PD). Recent studies on the relationship between herpes zoster (HZ) and PD have been conflicting, however.
A new study led by the London School of Hygiene & Tropical Medicine sought to investigate whether HZ is associated with incident PD risk in a matched cohort study using VA data about U.S. veterans. Participating in the research were the Michael E. DeBakey VAMC in Houston, the VA Connecticut Healthcare System in West Haven and associated academic institutions.
The study team compared the risk of PD between patients with incident HZ matched to as many as five individuals without a history of HZ using Cox proportional hazards regression. Their findings were published in the journal Movement Disorders.1
Results indicate that, among 198,099 HZ patients and 976,660 matched individuals without HZ (median age 67.0 years (interquartile range [IQR 61.4-75.7]); 94% male; median follow-up 4.2 years [IQR 1.9-6.6]), HZ was not associated with an increased risk of incident PD overall (adjusted HR 0.95, 95% CI 0.90-1.01) or in any sensitivity analyses.
“We found no evidence that HZ was associated with increased risk of incident PD in this cohort,” the authors wrote.
“The global burden of Parkinson’s disease (PD) is rising rapidly with population growth and aging.1 Neurodegeneration in PD, which is characterized by α-synuclein aggregates (Lewy bodies) leading to the loss of midbrain dopaminergic neurons, may occur decades before clinical PD diagnosis,” according to the researchers. “Its complex etiology remains poorly understood. Around 22% of PD risk is accounted for by genetic variation; although associations with several environmental factors have been described, risks of reverse causation, residual confounding, and other biases raise concerns about whether these associations are causal.”
The authors noted that the strongest epidemiological evidence for a relationship with infections comes from large studies showing a long-term increase in the risk of incident PD with influenza, influenza/pneumonia, viral hepatitis or any hospitalized infection occurring at least five years earlier.
“Studies of herpes zoster (HZ), caused by reactivation of the neurotropic varicella zoster virus that is nearly ubiquitous in adult populations, show conflicting results,” they pointed out. “Whereas two matched cohort studies using the Taiwanese National Health Insurance Research Database (NHIRD) found increases in PD risk after HZ (HR 1.80 [95% CI: 1.43-2.28]9 and HR 1.17 [95% CI: 1.10-1.25]), a nested case-control study using U.S. Medicare claims data showed an inverse association OR 0.88 (95% CI: 0.85-0.91).”
We therefore aimed to investigate the association between HZ and incident PD risk in the largest integrated healthcare system in the U.S., the Department of Veterans Affairs (VA), using a matched cohort study design.
- Tunnicliffe L, Weil RS, Breuer J, Rodriguez-Barradas MC, Smeeth L, Rentsch CT, Warren-Gash C. Herpes Zoster and Risk of Incident Parkinson’s Disease in US Veterans: A Matched Cohort Study. Mov Disord. 2024 Feb;39(2):438-444. doi: 10.1002/mds.29701. Epub 2024 Jan 16. PMID: 38226430; PMCID: PMC10922272.
