England BR, et al. – In this retrospective study, the clinicians focused on the epidemiologic association of herpes zoster (HZ) events with incident giant cell arteritis (GCA). They discovered that HZ was associated with increased GCA risk. HZ was identified as only one potential trigger for GCA due to the infrequency of HZ in GCA patients. Moreover, antivirals and vaccination did not consistently alleviate this risk.

Methods

• Two, large, independent US administrative datasets (Medicare 5% and Truven MarketScan) were applied with eligible subjects having 12 months of continuous coverage, >50 years old, and without history of GCA or polymyalgia rheumatica.
• By ICD–9 codes from physician visits or hospital discharges, HZ events (complicated and uncomplicated) and GCA were identified.
• Antiviral therapies and vaccinations were identified as prescription claims and drug codes. 
• With multivariable Cox proportional hazards regression, risk of incident GCA was calculated.

Results

• Among 16,686,345 subjects, 5,942 GCA cases occurred with 3.1% (MarketScan) and 6.0% (Medicare) having preceding HZ events.
• Findings showed that unadjusted GCA incidence rates were highest in those with complicated and uncomplicated HZ.
• After multivariable adjustment, complicated HZ was associated with an increased risk of GCA (MarketScan Hazard ratio [HR] 2.16, 95% confidence interval (CI) 1.46–3.18; Medicare HR 1.99, 95% CI 1.32–3.02) as was uncomplicated HZ (MarketScan HR 1.45, 95% CI 1.05–2.01; Medicare HR 1.42, 1.02–1.99). 
• Vaccination and antiviral treatment were not consistently associated with GCA risk, though antivirals were marginally associated with a decreased risk of GCA in Medicare (HR 0.67, 95% CI 0.46–0.99).