Association of herpes zoster with dementia and effect of antiviral therapy on dementia: a population-based cohort study

We investigated the association between herpes zoster (HZ) and dementia, and the effects of antiviral therapy on the risk of dementia. We used the National Health Insurance Service-National Sample Cohort in South Korea to identify individuals that were followed from January 1, 2002, to December 31, 2013. Occurrences of HZ and dementia were identified using the relevant diagnostic codes. Dementia was defined as the presence of diagnostic codes and history of anti-dementia drug prescription. Propensity score matching (1:1) was carried out among HZ patients according to antiviral therapy. A total of 229,594 individuals aged >= 50 years were analyzed. The incidences of the first-diagnosed HZ and dementia were 16.69 and 4.67 per 1000 person-years (PY), respectively. HZ patients had a higher risk of dementia (incidence rate ratio [IRR], 1.94 [95% CI 1.83-2.06]; adjusted hazard ratio [HR], 1.12 [95% CI 1.05-1.19]). Of the 34,505 patients with HZ, 28,873 (84%) had received antiviral treatment. The crude incidence rates of subsequent dementia in the treated and untreated groups were 7.79 and 12.27 per 1000 PY, respectively, resulting in an IRR of 0.64 (95% CI 0.56-0.72) and covariate-adjusted HR of 0.79 (95% CI 0.69-0.90). After propensity score matching, the treated group showed a significantly lower risk of dementia (HR 0.76; 95% CI 0.65-0.90). In this large population-based cohort study, HZ was associated with a higher risk of dementia. The use of antiviral agents in HZ patients was associated with lower risks of dementia.