Herpes zoster (HZ) is a common disorder that causes substantial pain and morbidity. We examined its rate and predictors in rheumatoid arthritis (RA) and non-inflammatory musculoskeletal (MSK) disorders to determine if HZ was increased in RA and whether treatment contributed to the risk of HZ.
After excluding patients witzh prior HZ, we assessed 10 614 RA and 1721 MSK patients by semi-annual questionnaires during 33 825 patient-years of follow-up. Predictors of HZ were determined by Cox regression and expressed as hazard ratios (HR) and 95% confidence intervals (CI).
The annualized incidence rate per 1000 patient-years was 13.2 (95% CI 11.9-14.5) in RA and 14.6 (95% CI 11.2-18.1) in MSK, and did not differ significantly after adjustment for age and sex. HZ was predicted by impaired functional status, as measured by the Health Assessment Questionnaire (HAQ), [HR 1.3 (95% CI 1.1-1.5)] and by the use of COX-2-specific non-steroidal anti-inflammatory drugs (NSAIDs) [HR 1.3 (95% CI 1.1-1.6)] in RA and MSK. In multivariable analyses in patients with RA, cyclophosphamide HR 4.2 (95% CI 1.6-11.5), azathioprine HR 2.0 (1.2-3.3), prednisone HR 1.5 (1.2-1.8), leflunomide HR 1.4 (1.1-1.8) and COX-2 NSAIDs HR 1.3 (95% CI 1.1-1.6) were significant predictors of HZ.
The incidence of HZ is increased in RA and MSK compared with population-based rates. However, the rate of HZ in RA is not increased compared with MSK. After adjustment for severity, various treatments, but not methotrexate or biologics, were risk factors for HZ.